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Manual ofNeuro-ophthalmology

Manual ofNeuro-ophthalmology

Amar Agarwal MS FRCS FRCOphth

Athiya Agarwal MD DO

Dr Agarwal’s Group of Eye Hospitals and Eye Research Centre19, Cathedral Road, Chennai - 600 086, India

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Manual of Neuro-ophthalmology© 2008, Jaypee Brothers Medical Publishers

All rights reserved. No part of this publication should be reproduced, stored in a retrieval system,or transmitted in any form or by any means: electronic, mechanical, photocopying, recording, orotherwise, without the prior written permission of the authors and the publisher.

This book has been published in good faith that the material provided by authors is original.Every effort is made to ensure accuracy of material, but the publisher, printer and authors willnot be held responsible for any inadvertent error(s). In case of any dispute, all legal mattersare to be settled under Delhi jurisdiction only.

First Edition: 2009ISBN 978-81-8448-411-3

Typeset at JPBMP typesetting unitPrinted at Ajanta

This book is dedicatedto a lovely couple

Marguerite Mcdonald and Stephen Klyce

Amar Agarwal MS FRCS FRCOPHTHDr. Agarwal’s Group of Eye Hospitalsand Eye Research Centre19, Cathedral RoadChennai-600 086, [email protected]

Athiya Agarwal MD DODr. Agarwal’s Group of Eye Hospitalsand Eye Research Centre19, Cathedral RoadChennai-600 086, [email protected]

Garrett Smith MDMoran Eye CenterSalt Nake City, UTAHUSA

Jeyalakshmi Govindan DO DNBConsultant OphthalmologistDr. Agarwal’s Eye Hospital19, Cathedral RoadChennai, India

Nick Mamalis MDMoran Eye CenterSalt Nake City, UTAHUSA

P Ramesh MBBS DMRD DNB MNAMS FRCRDirector, Liberty ScansChennai, India

Priya Narang MSNarang Eye HospitalAhmedabad, Gujarat, India

Contributors

viii Manual of Neuro-ophthalmology

Reena M Choudhry MD DO DNB FRCSIcare Eye Hospital and Postgraduate InstituteNoida, Uttar PradeshIndia

Sameer Narang MSNarang Eye HospitalAhmedabad, GujaratIndia

Saurabh Choudhry MD DO DNBIcare Eye Hospital and Postgraduate InstituteNoida, Uttar PradeshIndia

S Soundari DO DNB FRCSConsultant OphthalmologistDr. Agarwal’s Eye Hospital19, Cathedral RoadChennaiIndia

Neuro-ophthalmology is a complex subspecialty which requires keenskills of clinical observation, attention to detail, and intricate thoughtprocesses in order to formulate the appropriate diagnostic andtherapeutic plan for the patient. What makes the field even morechallenging is our limited knowledge of the intricate neurologicalpathways between the eye and the brain; many of which are stillbeing discovered, as long as our understanding is evolving.

To concisely and accurately explain the basics of neuro-ophthalmology is a difficult task, as it requires a thoroughunderstanding of the subject as well as a natural gift for simplifyingand organizing the material so that it appeals to a wide audience.Through the process of teamwork, the Agarwals’ have succeeded increating an outstanding book for neuro-ophthalmology that will proveto be an excellent reference for a full spectrum of readers, from medicalstudents to practising ophthalmologists.

Prof Amar Agarwal once explained to me that for any challengingsituation, “The battle is in the brain”. Whether the task is climbingMount Everest or writing a complete library of ophthalmology texts,the true challenge is in mind. Having the drive and determination tosucceed, no matter the situation, is the mark of a true pioneer, and acharacteristic of one of my strongest mentors, Prof Amar Agarwal.

Uday Devgan MD FACSChief of Ophthalmology

Olive View-UCLA Medical CenterUCLA School of Medicine

Private Ophthalmic PracticeMaloney Vision Institute

Los Angeles, California, USA

Foreword

Understanding Neuro-ophthalmology is a challenge. It took us a longtime to comprehend the basics in this field when we were residents.That is the notion why we have written Manual of Neuro-ophthalmology.The idea is that you dear reader can go through the text and figuresand never have difficulty in understanding this subject like we did.

We would like to thank our consultant Dr S Soundari for helpingus. Shri JP Vij and his full team of M/s Jaypee Brothers MedicalPublishers have always supported our writing endeavors. Our sincerethanks to them. Finally, dear reader we hope this book will changeyour outlook to Neuro-ophthalmology.

Amar Agarwal

Athiya Agarwal

Preface

1. Supranuclear Pathways for Eye Movements ..................................... 1Athiya Agarwal, Amar Agarwal

2. Supranuclear Disorders of Eye Movements ....................................17Athiya Agarwal, Amar Agarwal

3. Nystagmus .............................................................................................32Athiya Agarwal, Amar Agarwal

4. The Pupil ................................................................................................54Athiya Agarwal, Amar Agarwal

5. Visual Pathway .....................................................................................73Athiya Agarwal

6. Anatomy of the Optic Nerve ............................................................ 103Athiya Agarwal

7. Oculomotor Nerve ............................................................................. 109Athiya Agarwal

8. Lesions of the Oculomotor Nerve ................................................... 118Athiya Agarwal

9. Trochlear Nerve and its Lesions ..................................................... 123Athiya Agarwal

10. Abducent Nerve and its Lesions ..................................................... 132Athiya Agarwal

11. Trigeminal Nerve .............................................................................. 140Athiya Agarwal

12. Facial Nerve and its Lesions ............................................................ 145Athiya Agarwal

13. Congenital Optic Nerve Anomalies ................................................ 150Priya Narang, Sameer Narang, Amar Agarwal

14. Optic Nerve Tumors ......................................................................... 157Nick Mamalis, Garrett Smith

15. Abnormalities of Optic Nerve Head .............................................. 185Reena M Choudhry, Saurabh Choudhry, Amar Agarwal

16. Ocular Myopathies ............................................................................ 197S Soundari

17. Miscellaneous .................................................................................... 204Jeyalakshmi Govindan, S Soundari

18. Examination of a Neuro-ophthalmology Case .............................. 219S Soundari

19. Imaging in Neuro-ophthalmology .................................................. 226P Ramesh

Index ..................................................................................................... 253

Contents

1Supranuclear

Pathways for EyeMovements

Athiya Agarwal, Amar Agarwal

INTRODUCTION

One is always confused about supranuclear pathways. We understandthe pathways of the III, IV and VI cranial nerve nuclei. We would beable to trace it from the brain to the superior orbital fissure, but wefail to remember that these pathways we are discussing are theinfranuclear pathways which extend from the cranial nerve nuclei tothe ocular muscle. We need to also understand the anatomy of thesupranuclear pathways.1,2

SUPRANUCLEAR AND INFRANUCLEAR PATHWAYS

Anatomical pathways, which extend from the cortical centers of thebrain to the cranial nerve nuclei, are called the supranuclear pathways.From the cranial nerve nuclei to the ocular muscle exist the infranuclearpathways (Fig. 1.1).

In peripheral nerves, the nerve starts from the brain and reachesthe anterior horn cell in the spinal cord. This is the upper motorneuron. From the anterior horn cell of the spinal cord, the nerve movesto the peripheral muscle. This is the lower motor neuron. If there is alower motor neuron disease the limb is flaccid and if there is an uppermotor neuron disease the limb is spastic.

The cranial nerve nuclei are like peripheral nerve nuclei. From thecortex of the brain the nerve extends to the cranial nerve nuclei andthis is the upper motor neuron (UMN) pathway. From the cranialnerve nuclei the nerve extends to the ocular muscle and this is thelower motor neuron (LMN) pathway. In peripheral nerves if theanterior horn cell gets involved as in poliomyelitis, the patient has aLMN disease and so the limb is flaccid. The anterior horn cell is akinto the cranial nerve nuclei of cranial nerves. So, if the cranial nervenuclei gets involved the lesion produced will be a LMN lesion.

2 Manual of Neuro-ophthalmology

Fig. 1.1: Supranuclear pathway

SUPRANUCLEAR EYE MOVEMENT SYSTEMS

There are five supranuclear eye movement systems. They are:1. Saccadic system2. Pursuit system3. Vergence system4. Non-optic reflex system5. Position maintenance system.

SACCADIC SYSTEM

The saccadic system is otherwise known as the fast eye movementsystem or rapid eye movement system. This is because the saccadicsystem controls the fast eye movements. These are commandmovements. For example if we say, look to the right, the eyes turn tothe right. This occurs rapidly and is a rapid eye movement. The system,which controls this command pathway, is the saccadic system.

The saccadic system originates from the frontal lobe of the brain.The impulses then move to the mesencephalic system and so theanatomical pathway subserving the fast eye movements is the

Supranuclear Pathways for Eye Movements 3

frontomesencephalic pathway. When you watch someone watching a gameof tennis or table tennis, you will notice the eyes move rapidly fromone end of the court or table to the other. The eyes keep on dartingfrom one end to the other. These are fast eye movements controlledby the frontomesencephalic pathway.

Horizontal Saccades

The saccades can in turn be horizontal or vertical. In horizontalsaccades, the eyes move horizontally and in vertical saccades, theeyes move up and down. Let us now understand the pathway of thehorizontal saccades (Fig. 1.2).

Fig. 1.2: Horizontal saccade pathwayLR- Lateral rectus; MR- Medial rectus; LE- Left eye; RE- Right eye; Occ.Lobe-Occipital Lobe; Fron.lobe- Frontal lobe; III- III Cranial nerve nucleus; VI- VI Cranialnerve nucleus; PGC- Pontine gaze center; MLF- Medial longitudinal fasciculus;UMN Pathway- Upper motor neuron pathway; LMN Pathway- Lower motor neuronpathway


If the eyes have to look to the right, then the command for thismovement is given by the left frontal lobe in area 8 of the cortex. Thenerves cross over to the opposite side and reach the right pontinegaze center. From here the nerves pass to the same side (in this casethe right) VI nerve nuclei. From the right pontine gaze center nervesalso pass to the opposite III nerve nuclei. In this case this will be theleft III nerve nuclei. All the cranial nerve nuclei are connected witheach other through the medial longitudinal fasciculus or mediallongitudinal bundle. In other words from the right pontine gaze center,the nerves pass through the medial longitudinal bundle to the left IIIcranial nerve nuclei. Till here is the supranuclear pathway. This iswhy this is also called the frontomesencephalic pathway.

From the right VI nerve nucleus nerves then pass to the lateralrectus muscle of the right eye. From the left III nerve nucleus nervespass to the left medial rectus muscle. These are the infranuclearpathways and both the eyes move to the right.

At this stage it is important to understand a bit more on themedial longitudinal bundle. As just explained, the nerves pass fromthe pontine gaze center to the VI and III nerve nuclei through themedial longitudinal bundle. If there is a lesion in the mediallongitudinal bundle, these fibers are cut and there would not be acorrelation between the III nerve and the VI nerve. This leads to thecondition called internuclear ophthalmoplegia.

Vertical Saccades

The pathway for the vertical saccades is still doubtful. Vertical saccadesdepend on simultaneous bilateral activity within the frontal lobes inArea 8 (Fig. 1.3). This means that the horizontal saccades areunilaterally controlled whereas the vertical saccades are bilaterallycontrolled.

If one has to look up or down, impulses travel from both the frontallobes in Area 8. The impulse travels via the basal ganglia to the pretectalarea or the pretectal center for vertical gaze. This is the vertical gazecenter. From the vertical gaze center impulses pass to the III nervenuclei. Till here is the supranuclear pathway. Now, the infranuclearpathway starts and impulses go via the III cranial nerve to the verticalmuscles and the patient looks up or looks down.

Because of the fact that vertical saccades require bilateral corticalactivity, cerebral hemisphere lesions rarely produce deficits in thevertical saccades. Such deficits are seen only with massive hemisphericlesions producing bilateral damage to both frontomesencephalic


pathways. Disturbances of vertical saccades are much more commonwith midbrain disorders.

Characteristic of the Saccade

The characteristic of the saccades is shown in Table 1.1 compared tothe other supranuclear eye movements. From the onset of the stimulus,which is voluntary to the beginning of the recorded saccade, the latentperiod is about 200 to 250 msec. The velocity of the fast eye movementis 30 to 700 degrees/second.

Fig. 1.3: Vertical saccade pathwayLE- Left eye; RE- Right eye; Occ.Lobe- Occipital Lobe; III- III Cranial nerve nucleus;VI- VI Cranial nerve nucleus; PGC- Pontine gaze center; MLF- Medial longitudinalfasciculus; UMN Pathway- Upper motor neuron pathway; LMN Pathway- Lowermotor neuron pathway


PURSUIT SYSTEM

The smooth pursuit system is utilized when the eyes follow targetsthat move smoothly and relatively slowly. It maintains a fixedrelationship between the movements of the eyes and the target. Assmooth pursuit movements directly relate eye position to targetposition, they are also termed as following or tracking movements. Asthese movements are slow, they are called slow eye movements. Imaginea person walking and you are watching that person. When your eyesfollow the movement of the person, they will be using the pursuitsystem. The pathway for the pursuit system starts from the occipitallobe and hence is known as the occipitomesencephalic pathway. Thereare different pathways for horizontal pursuits and for vertical pursuits.

Horizontal Pursuit System Pathway

If a target is moving to the right (Fig. 1.4), the first step is that theeyes have to visualize the object. So the pathway starts from the retina

Fig. 1.4: Horizontal pursuit pathway (slow phase)LR- Lateral rectus; MR- Medial rectus; LE- Left eye; RE- Right eye; Occ.Lobe-Occipital Lobe; Fron.lobe- Frontal lobe; III- III Cranial nerve nucleus; VI- VI Cranialnerve nucleus; PGC- Pontine gaze center; MLF- Medial longitudinal fasciculus;UMN Pathway- Upper motor neuron pathway; LMN Pathway- Lower motor neuronpathway


of both eyes. The impulses pass through the optic nerve, optic chiasma,and optic tract and reach the right occipital lobe in area 19. This areasubserves the pursuit movements. It is important to note that theoccipital areas mediate horizontal pursuit movements to the ipsilateralside. In other words, the right occipital lobe mediates horizontalpursuit movements to the right.

From the occipital lobe, impulses go to the same side pontine gazecenter. In this case, impulses from the right occipital lobe go to theright Pontine gaze center. From here impulses go to the right VI nervenucleus and the left III nerve nucleus. Till here is the supranuclearpathway. From the right VI nerve nucleus and the left III nerve nucleusimpulses go via the infranuclear pathway to the lateral rectus and themedial rectus. The characteristics of the pursuits are shown inTable 1.1.

Corrective Saccade

When the target is moving away from the field of vision the eyeswhich were moving slowly to that side have to come back to theiroriginal position. A fast eye movement does this, in other words asaccade. This is the corrective saccade. If a stream of cars are going infront of our vision, then we keep on following one car and when itgoes out of the field of vision our eyes would come and fixate back tothe car in the center of our field of vision. This would be done by thecorrective saccade.

As the impulses from the target moving to the right reaches theoccipital lobe (Area 19) and the object is going out of the field of

Table 1.1: Characteristics of eye movements

Type Stimulus Latency Velocity Amplitude Conjugacy(msec) (Deg./Sec) (Degrees)

1. Saccade Volition, reflex 200 30-700 0.5-9.0 Conjugate2. Pursuit Target motion 125 < 50 0-90 Conjugate3. Vergence Accommodative, 160 < 20 Age Disjugate

fusional dependent4. Vestibulo- Head movement <100 < 400 0-90 Conjugate

ocular5. Corrective Positions error 125 < 150 < 4 Conjugate

saccade6. Micro- Fixation - 3-12 1-25 Conjugate

saccade7. Microdrift Fixation - 0-30 <1 Disjugate

min/sec


vision the occipital lobe sends impulses to the ipsilateral frontal lobeto perform the corrective saccade. In this case the right occipital lobe(Fig. 1.5) sends impulses to the right frontal lobe (Area 8). This meansthere has to be a communication between the occipital lobe and thefrontal lobe. From the right occipital lobe impulses pass to the frontallobe via the parietal lobe.

From the right frontal lobe, impulses then pass to the left pontinegaze center which in turn sends impulses to the left VI nerve nucleusand the right III nerve nucleus. This is the supranuclear pathway.Then, the infranuclear pathway takes over and impulses go to therespective lateral and medial recti and the eyes move to the left as afast eye movement. This is the corrective saccade.

Fig. 1.5: Corrective saccade (Horizontal pursuit pathway for the fast phase)LR- lateral rectus; MR- Medial rectus; LE- Left eye; RE- Right eye; Occ.Lobe-Occipital Lobe; Fron.lobe- Frontal lobe; III- III Cranial nerve nucleus; VI- VI Cranialnerve nucleus; PGC- Pontine gaze center; MLF- Medial longitudinal fasciculus;UMN Pathway- Upper motor neuron pathway; LMN Pathway- Lower motor neuronpathway


One can illustrate this with an optokinetic drum, which is a drumwith black and white stripes. The drum is rotated and the eyes fixateon it. When the stripes go away from the field of vision, the correctivesaccade occurs. This leads to a type of nystagmus known as opto-kinetic nystagmus.

Parietal Lobe Lesion

If the person has a parietal lobe lesion, then there is a problem (Fig.1.6). When the corrective saccade has to work the impulse would notpass beyond the parietal lobe. Thus, this would lead to a deficit in thecorrective saccade. So a deep parietal lobe lesion causes loss or decreaseof the fast phase of the optokinetic nystagmus, when movement ofthe drum is towards the side of the lesion.

Fig. 1.6: Parietal lobe lesionLR- Lateral rectus; MR- Medial rectus; LE- Left eye; RE- Right eye; Occ.Lobe-Occipital Lobe; Fron.lobe- Frontal lobe; III- III Cranial nerve nucleus; VI- VI Cranialnerve nucleus; PGC- Pontine gaze center; MLF- Medial longitudinal fasciculus;UMN Pathway- Upper motor neuron pathway


Vertical Pursuit System

Vertical pursuit movements are generated by simultaneous bilateralstimulation of area 19 of the occipital lobe (Fig. 1.7). The axons of theoccipital lobe descend to the pretectal area. From the pretectal areaimpulses travel to the III nerve nuclei. Till here is the supranuclear orUMN pathway. Then from the III nerve nuclei, impulses pass to thevertical muscles via the infranuclear pathway. The pretectal area orpretectal center is the center for vertical gaze, analogous to the pontinegaze center, which is the center for horizontal gazes.

Fig. 1.7: Vertical pursuit pathwayLE- Left eye; RE- Right eye; III- III Cranial nerve nucleus; VI- VI Cranial nervenucleus; PGC- Pontine gaze center; MLF- Medial longitudinal fasciculus; UMNPathway- Upper motor neuron pathway; LMN Pathway- Lower motor neuronpathway


VERGENCE SYSTEM

The role of the vergence system is to keep the image of a target onappropriate points (corresponding elements) of the two retinas bycontrolling the visual axes of the eyes. Thus, vergence is utilizedwhenever a target falls on noncorresponding retinal elements. Forexample, if a target is moved towards the eyes, they must turn towardeach other (converge) to keep the target on the fovea of each eye.Conversely, as the target is moved further away, the eyes must turnout (diverge) (Actually, divergence does not occur in our eyes.)Vergence is thus a disconjugate (nonparallel) movement of the eyes,in contrast to most other eye movements which are conjugate (parallel).There are two types of vergence. They can be voluntary—when wecommand our eyes to converge or reflex—when we bring an objector tape towards our nose and the eyes converge while fixating on theobject. The characteristics of the vergence movements are shown inTable 1.1.

Voluntary Vergence

The center for voluntary vergence is situated in area 8 of the frontallobe (Fig. 1.8). If one wants to converge then a command movementis sent from area 8. These are bilateral impulses and they go to thepretectal area via the basal ganglia. Here there is the convergencearea. From the convergence area, impulses go bilaterally to the IIIand VI nerve nuclei. Till here is the supranuclear pathway. From theIII nerve nuclei impulses go to the medial recti to converge. From theVI nerve nuclei inhibitory impulses go to the lateral recti so that theeyes can converge. Thus both the eyes converge.

Pursuit or Reflex Vergence

In this, the impulses originate from the retina of the two eyes (Fig.1.9). If a pen is held in front of our eyes and moved towards the noseand if we keep looking at the pen, then the impulses from the twoeyes will make the eyes converge by the pursuit vergence pathway.From the retina impulses will go via the optic nerve and tract to area19 of the occipital lobe. This is a bilateral impulse. From here it goesto the pretectal area where it reaches the convergence area. Fromhere impulses pass bilaterally to the III and VI nerve nuclei. This isthe supranuclear pathway. Then positive impulses go to the medialrecti and inhibitory impulses to the lateral recti and the eyes convergewhile looking at the object.


Fig. 1.8: Voluntary vergence pathwayLR- Lateral rectus; MR- Medial rectus; LE- Left eye; RE- Right eye; Occ.Lobe-Occipital Lobe; Fron.lobe- Frontal lobe; III- III Cranial nerve nucleus; VI- VI Cranialnerve nucleus; PGC- Pontine gaze center; MLF- Medial longitudinal fasciculus;UMN Pathway- Upper motor neuron pathway; LMN Pathway- Lower motor neuronpathway

NON-OPTIC REFLEX SYSTEM

The non-optic reflex system integrates eye movements and the bodymovements. There are basically three systems in this: (i) semicircularcanals, (ii) neck receptors, and (iii) the cerebellum. The characteristicsare shown in Table 1.1.


Fig. 1.9: Pursuit or reflex vergence pathwayLR- Lateral rectus; MR- Medial rectus; LE- Left eye; RE- Right eye; III- III Cranialnerve nucleus; VI- VI Cranial nerve nucleus; PGC- Pontine gaze center; MLF-Medial longitudinal fasciculus; UMN Pathway- Upper motor neuron pathway; LMNPathway- Lower motor neuron pathway

Semicircular Canals

If a lateral semicircular canal is stimulated, the non-optic reflex systemstarts to work. If the head is rotated to the left (Fig. 1.10), the lateralsemicircular canal is stimulated. If we tilt our head to the left, theeyes should generally keep looking straight ahead (the ultimate aimof the whole process). For the eyes to look straight ahead when we


Fig. 1.10: Non-optic reflex system pathwayLR- Lateral rectus; MR- Medial rectus; LE- Left eye; RE- Right eye; III- III Cranialnerve nucleus; VI- VI Cranial nerve nucleus; PGC- Pontine gaze center; MLF-Medial longitudinal fasciculus; VN- Vestibular nucleus; UMN Pathway- Uppermotor neuron pathway; LMN Pathway- Lower motor neuron pathway

have tilted our head to the left the eyes will move to the right. Trythis on yourself by tilting your head to the left. You will note youreyes move to the right so that you keep on looking straight ahead.

When the semicircular canal is stimulated, impulse goes to the sameside (in this case left side) vestibular nucleus. From the left vestibularnucleus, impulses go to the opposite side pontine gaze center whichin turn send impulses to the right VI nerve nuclei and left III nervenucleus. This is the supranuclear pathway. Then the infranuclear


pathway takes over to the right lateral rectus and left medial rectusand the eyes turn towards the right. This constitutes the vestibularinfluence on eye movements.

Neck Receptors

Contributory information also comes from the proprioceptive organsof the neck muscles via the spinovestibular tract.

Cerebellum

The role of the cerebellum is not very clear. There is a prominentflocculo-oculomotor tract, which is the only direct cerebellarconnection with the eye nerve nuclei. This pathway connects with theopposite III nerve nuclei and the same side VI nerve nuclei (exactlyopposite the semicircular canal connection, which connects with thesame side III nerve and opposite side VI nerve nuclei). Thus, the eyestend to move in the opposite direction. This pathway may help explainthe reason why nystagmus in cerebellar disease is in the oppositedirection to that occurring in vestibular disease.

POSITION MAINTENANCE SYSTEM

The function of the position maintenance system is to maintain anobject of interest on the fovea or to maintain a specific gaze position.It is the most complex of eye movements and works efficiently onlywhen the person is alert. It becomes seriously disturbed when theperson’s level of consciousness is depressed. The micromovementsystems use the same substrates as its macrocounterparts, but thedetails of the pathways are not yet known.

The micro eye movements are known as microsaccades or flicksand micropursuits or drifts. The microsystem is continuously activein maintaining the target precisely on the fovea, presumable whileother eye movement systems are active as well. Hence, it is the ultimatemonitor of eye movements, coordinating all the other eye movementsystems and determining the precise position of the eye with respectto the target as well as to the head and body. Stated simply, when anobject moves more rapidly than the smooth pursuit system can followit, a saccadic compensation is made to maintain the eye position relativeto the moving target. The pursuit system has been overcome by theposition maintenance system.

Take an example of your catching a ball. At that time when theball is in the air, your saccadic and pursuit systems work so that your


eyes are on the ball. Sometimes, there would be an overshooting ofeither of the systems and at that time the micromovements ofmicrosaccades and micropursuits take over so that you finally catchthe ball.

SUMMARY

Thus, there are basically five supranuclear pathways, which controleye movements. It is important to know them if one wants tounderstand supranuclear lesions.

REFERENCES

1. Sunita Agarwal, Athiya Agarwal, et al. Textbook of Ophthalmology 4th vol;Jaypee, India 2003.

2. Amar Agarwal. Handbook of Ophthalmology; Slack USA 2005.

2SupranuclearDisorders of

Eye MovementsAthiya Agarwal, Amar Agarwal

INTRODUCTION

If paralysis of an eye muscle occurs due to a lesion in the muscle,nerve or the nerve nucleus, all the functions of the muscle are involved.For example, if an infranuclear lesion occurs in the medial rectus, thepatient will neither be able to adduct the eye nor be able to performconvergence as the medial rectus is paralyzed. If the lesion was asupranuclear lesion, then the patient would not be able to performconvergence but would be able to adduct the eye. The supranuclearlesions are lesions above the cranial nerve nucleus.1,2

PSEUDO-OPHTHALMOPLEGIA

In supranuclear lesions, only those activities controlled by theparticular region involved are impaired and other movements eventhough carried out by the same muscle remain normal. This paralysisof one type of movement and not of another is called pseudo-ophthalmoplegia.

CLASSIFICATION

Depending on the supranuclear pathway, we can classify the supranuclearlesions as:• Saccadic disorders• Pursuit disorders• Vergence disorders• Non-optic reflex system disorders (Flow chart 2.1).

SACCADIC DISORDERS

Saccadic disorders can in turn be divided into two groups (Flow chart 2.1):• Conjugate palsies• Dissociated palsies.


Flow chart 2.1: Supranuclear pathway lesions

In dissociated palsies, there is a misalignment of the eyes as theconjugate movements become dissociated, whereas in conjugate palsiesboth the eyes fail to look in one direction. In dissociated palsies, oneeye fails to move in a particular direction, whereas the other eyemoves in that direction.

CONJUGATE PALSIES

Depending on the site of lesion, conjugate palsies can be grouped andclassified (Flow chart 2.2). The site of lesion could be in the frontallobe, basal ganglia, etc. In other words an area subserving the saccadicpathway if involved would lead to conjugate palsies.

Lesions of the Frontal Cortex

Overactivity

Epileptic seizures arising in the appropriate area of the frontal cortexcause what are called frontal adversive attacks. In these episodes, theattack commences with the head and eyes being forcibly deviatedaway from the discharging frontal cortex. If the left frontal cortex hasan overactivity due to a discharging focus and area 8 is involved, thesaccadic system overworks and the eyes look to the opposite sidethat is to the right (Fig. 2.1).

The side of the body to which the deviation has occurred maythen be involved by focal motor activity and ultimately the attackmay progress to a generalized seizure (Fig. 2.2).

Supranuclear Disorders of Eye Movements 19

Flow chart 2.2: Conjugate palsies

Fig. 2.1: Frontal lobe overactivity: Frontal adversive seizureLR- Lateral rectus; MR- Medial rectus; LE- Left eye; RE- Right eye; Occ.Lobe-Occipital Lobe; Fron.lobe- Frontal lobe; III- III Cranial nerve nucleus; VI- VI Cranialnerve nucleus; PGC- Pontine gaze center; MLF- Medial longitudinal fasciculus


Fig. 2.2: Frontal adversive attackOcc.Lobe- Occipital Lobe; Fron.lobe- Frontal lobe; PGC- Pontine gaze center

Unilateral Underactivity

Damage to the frontal eye field by a vascular lesion may render thepatient unable to look to the opposite side. This deficit is rarely seenas rapid compensation occurs and the eye movements appear to benormal within hours. However, residual evidence may be found inthe patient having difficulty in maintaining gaze in that direction orin the development of some nystagmus caused by this weakness whenattempting to do so. If the patient is subsequently comatose oranesthetized, the eyes will deviate towards the damaged side of thecortex, because of the unopposed activity of the intact opposite frontallobe.


If the left side of the frontal area is damaged (Fig. 2.3), the intactarea 8 on the right side acts. This in turn pushes the eyes to the leftside, in other words, to the side of the lesion. The left hemispherecauses a right hemiparesis and the eyes thus look away from the para-lyzed limbs.

Bilateral Underactivity

Bilateral lesions of the frontomesencephalic pathway cause saccadicpalsy in both directions with preservation of pursuit and other eyemovements. Bidirectional saccadic palsy necessitates utilization of headmovements for refixation. The eyes remain locked on the originalobject of regard during a rapid head movement. This is called spasmof fixation. Bilateral saccadic palsies could be congenital or acquired. If

Fig. 2.3: Frontal lobe underactivityOcc.Lobe- Occipital Lobe; Fron.Lobe- Frontal lobe; PGC- Pontine gaze center


acquired it could be due to multiple sclerosis, Wilson’s disease,Huntington’s chorea or lipidosis.

The most striking feature of this condition is the head thrusts utilizedto accomplish refixations. The head moves in the direction of theeccentric new target, as there is a saccadic palsy present. When thehead moves, the intact vestibulo-ocular system (non-optic reflexsystem) gets activated and the eyes are driven away from the attemp-ted direction of gaze. So, the patient closes the eyelids thus reducingthe vestibulo-ocular reflex gain and so reduces the amount of headthrust required. Head rotation overshoots the intended target,enabling the deviated eyes to fixate upon the object.

Lesions of the Basal Ganglia

Overactivity

The basal ganglia is predominantly concerned with movements in thevertical plane. Overactivity in the basal ganglia leads to the oculogyriccrisis. This usually consists of a fixed deviation of the eyes in anupward direction. During this crisis, the patient is incapacitated andany attempt to recover control of the eyes results merely in a feeblejerky displacement from the position of spasmodic displacement. Thehead is frequently turned in the same direction as the eyes. This occursin postencephalitic parkinsonism, posthead injury state, neurosyphilisor brain tumors.

Underactivity: Progressive Supranuclear Palsy

In progressive supranuclear palsy there is loss of nerve cells, vasculardegeneration’s and glial reactions in the basal ganglia and midbrain.The first manifestation of progressive supranuclear palsy is an inabilityto make vertical saccades, particularly downward saccades. At thispoint, the patients bang their shins, eat off only the top part of theirplates and complain of being unable to read (they cannot look down!).As the disease progresses, horizontal fast movements becomeinvolved as well. Eventually all fast eye movements are affected andthe pursuit movements become cogwheel.

Lesions of the Collicular Area

Parinaud’s Syndrome

There are several manifestations of lesions in the collicular area. Thesigns are thought to be caused by pressure and distortion of


underlying structures in the midbrain and not by damage to specificpathways traversing the colliculi. The general name for the clinicalpicture produced is known as Parinaud’s syndrome. Any combinationof impaired upward gaze, impaired downward gaze, pupillaryabnormalities or loss of accommodation reflex can occur. In general,loss of upward gaze associated with dilated pupils that are fixed tolight suggests a lesion at the level of the superior colliculus. Loss ofdownward gaze, normal pupillary reactions to light and loss ofconvergence suggest that the lesion is slightly lower in the area of theinferior colliculus. It could be due to lesions of the pineal gland,multiple sclerosis, vascular diseases or Wernicke’s encephalopathy.

A special type of nystagmus is present called retractory nystagmus.This is a very rare sign of disease in the collicular area and consists ofan inward and outward movement of both eyes when the patientattempts to look upwards. Presumably, it is produced by all theextraocular muscles acting simultaneously—jerking the globe back intothe orbit or attempted upward gaze—in an attempt to overcome theinability to look upwards.

DISSOCIATED PALSIES

In dissociated palsies, one eye moves in one direction whereas theother eye cannot move in the same direction. Thus, there is adissociation in the gaze movements. These canbe:• Internuclear ophthalmoplegia• One and one-half syndrome• Dissociated vertical palsies.

Internuclear Ophthalmoplegia

Introduction

Lesions affecting the pathways by which the various ocular nuclei arelinked together, i.e. lesions of the medial longitudinal fasciculus (MLF)or medial longitudinal bundle produces internuclear ophthalmoplegia.The MLF connects the III nerve and the VI nerve nuclei. If a lesionoccurs in this there is prevention of the harmonious coordination ofthese nuclei in producing conjugate movements. So, one eye carriesout a voluntary movement of gaze whereas the other eye does not,thus leading to failure of the conjugate (both eyes moving in the samedirection) movement. This leads to a misalignment of the eyes andthus to diplopia. This feature differentiates the internuclear palsiesfrom the other supranuclear lesions.


Etiology

Depending on the lesion being unilateral or bilateral, various causesof internuclear ophthalmoplegia are present (Flow chart 2.3). Thecommon causes are vascular lesions or multiple sclerosis.

Classification

Internuclear ophthalmoplegia (INO) are grouped into three types.They can be type I, type II or type III INO.

Type I-INO In type I INO, the lesion is near the III cranial nervenuclei including also the convergence area (Fig. 2.4). Essentially thereis paralysis of both medial recti. The impulses coming from the pontinegaze center go to the VI nerve and III nerve nuclei. As the connectionsto the VI nerve nuclei are not affected no disturbance is present inlateral rectus movements. The eyes are divergent due to bilateralinvolvement of the medial recti and there is loss of convergence. Itoccurs in hypertensive brainstem lesions and multiple sclerosis.Divergence may be complicated by skew deviation of the eyes inwhich one eye may be up and out and the other eye looks down andout. There may be a see saw nystagmus present in which the eyes jerkup and down alternately (Fig. 2.5).

Type II-INO In this relatively common variety of INO, the MLF isdamaged and the medial recti fail to move synchronously with thelateral recti (Fig. 2.6) on attempted lateral gaze to either side. Yetwhen each eye is tested alone, the medial recti function is evident butincomplete. Test this by covering the abducting eye and making theadducting eye follow the finger. In type II-INO convergence is normal

Flow chart 2.3: Etiology of inter nuclear ophthalmoplegia


Fig. 2.4: Site of lesions in internuclear ophthalmoplegiaIII- III Cranial nerve nucleus; VI- VI Cranial nerve nucleus; PGC- Pontine gazecenter; MLF- Medial longitudinal fasciculus

Fig. 2.5: Type I internuclear ophthalmoplegia


as the convergence area is not affected (Fig. 2.4). This occurs in multiplesclerosis, pontine glioma or in encephalitis.

Type III-INO The third variety of INO occurs in multiple sclerosis.In this type of INO (Fig. 2.7), none of the eye abducts completelywhile adduction is complete. The relay to the VI cranial nerve nucleiis affected on both sides (Fig. 2.4). If you test the eye individually byclosing the other eye, the eye would abduct differentiating this froman infranuclear lesion (VI nerve palsy).

One and One-Half Syndrome

One and one-half syndrome is also known as paralytic pontineexotropia. In the primary position the eye which is opposite the sideof lesion is exotropic. The eye on the same side of the lesion looksstraight ahead. The lesion is in the pontine paramedian reticular

Fig. 2.6: Type II internuclear ophthalmoplegia


formation (pontine gaze center—PGC) or VI nerve nucleus andipsilateral medial longitudinal fasciculus. From figure 2.8 one willunderstand that only the VI nerve on the side opposite the side of thelesion will work. The patient is not able to gaze with either eyetowards the side of the lesion and is not able to adduct the eye on theside of the lesion (Fig. 2.9). This is why this is called one and one-halfsyndrome as one side gaze is absent and on the other side half thegaze movement only is present.

Dissociated Vertical Palsies

A dissociated palsy may affect the elevators of one eye in a supranuclearpalsy due to a localized lesion close to the nuclei below the pointwhere the corticofugal pathway for elevation of the eyes bifurcatesinto the branches which go to both III nerve nuclei. In this event,

Fig. 2.7: Type III internuclear ophthalmoplegia


Fig. 2.8: One and one-half syndrome- Site of lesionIII- III Cranial nerve nucleus; VI- VI Cranial nerve nucleus; PGC- Pontine gazecenter; MLF- Medial longitudinal fasciculus

Fig. 2.9: One and one-half syndrome


conjugate vertical movements are dissociated, one eye being incap-able of elevation in voluntary movements but moving up normally inBell’s phenomenon.

PURSUIT DISORDERS

Overactivity

If there is an overactivity of the parieto-occipital cortex (read verticalpursuit pathway), seizures originating in the occipital cortex causedeviation of the eyes to the same side. But in this situation, themovements will be accompanied by visual hallucinations. These usuallyconsist of flashing lights and colored blobs. A generalized convulsionmay ensue but focal motor activity, other than the eye movements isnot a feature of a focal seizure arising in the occipital lobe.

Underactivity

Damage to the parieto-occipital cortex leads to the patient not able tofollow a target on the side of the lesion. If the patient has a rightoccipital lobe lesion, then the patient would not be able to follow thetargets to the right side. Damage to the parieto-occipital cortex isoften associated with either parietal lobe difficulties, which may maketesting impossible. Similarly, if a homonymous hemianopia coexists(as it often does if the lesion is a vascular one), the patient may beunable to follow an object because it keeps vanishing into thehemianopic field. In these cases, it is essential to keep the object to befollowed just inside the midline, in the intact half of the patient’svision and to move it slowly.

VERGENCE DISORDERS

Paralysis of Convergence

Paralysis of convergence occurs if the lesion is in the pretectal areaaffecting the convergence area (read vergence pathways in Chapter 1).It is characterized by a failure of convergence with crossed diplopiaof the concomitant type. When the eyes view a near object, togetherwith the absence of any limitation of movement on either eyeinductions or inversions in any part of the field.

Paralysis of Divergence

Paralysis of divergence is characterized by the appearance of aconvergent strabismus with uncrossed diplopia when the eyes view adistant object.


NON-OPTIC REFLEX SYSTEM DISORDERS

Vestibular System Disorders

The vestibular apparatus (semicircular canals) controls the non-opticreflex system. Any lesion affecting the semicircular canals, VIII nerveor the vestibular nuclei will seriously affect the push-pull effect of thevestibular control of eye movements.

The right-sided vestibular elements, normally push the eyes tothe left. If there is a lesion in the right vestibular apparatus, it willlead to weakness of the eye movements to the left side. On attemptinggaze to this side, the intact normal vestibular mechanism on the leftside, coupled with the weakness of the damaged right side will forcethe eyes to drift back to the midline. To solve this problem, there willbe a quick jerk of the eyes to the left side; i.e. to the side opposite theside of the lesion. The quick jerk in this case will be occurring to theleft side and the lesion was in the right side. Nystagmus is alwaystalked in relation to the fast phase of the nystagmus. In this case(right side vestibular lesion), the slow phase was on the right sideand to correct it a quick jerk or fast phase occurred towards the leftside. Thus, the nystagmus is away from the side of the lesion in a vestibulardisease (Fig. 2.10).

With destruction of the labyrinth by Ménière’s disease, nystagmusdoes not occur, because of central compensation for the absence ofany input. A similar situation exists after acute labyrinthine destructionwhen the initial imbalance settles. Similarly, in slowly occurringdamage to the VIII nerve (an acoustic nerve tumor) compensationoften prevents development of nystagmus. When it does occur in thissituation, it reflects brainstem or cerebellar damage from the extensionof the tumor into the cerebellopontine angle.

With central lesions of the vestibular apparatus (multiple sclerosis,vascular accidents) compensation cannot occur and the nystagmusand associated symptoms of vestibular damage tend to persist.

Cerebellar Disorder

The exact mechanism of cerebellar nystagmus is not known. Whennystagmus occurs it is opposite that found in a vestibular lesion. In aright-sided vestibular lesion, the slow phase of the nystagmus is tothe right and the fast phase to the left. This means the nystagmus is tothe left, in other words opposite the side of the lesion. In cerebellardisease, the fast phase of the nystagmus is on the same side of thelesion. So, if there is a right-sided cerebellar lesion, the fast phase of


Fig. 2.10: Vestibular lesionLR- Lateral rectus; MR- Medial rectus; LE- Left eye; RE- Right eye; Occ.Lobe-Occipital Lobe; Fron.lobe- Frontal lobe; III- III Cranial nerve nucleus; VI- VI Cranialnerve nucleus; PGC- Pontine gaze center; MLF- Medial longitudinal fasciculus;VN- Vestibular nucleus

the nystagmus is towards the right side. This could be due to theflocculo-oculomotor pathway, which works in the reverse of thevestibular pathway. The left vestibular pathway pushes the eyes tothe right whereas the left flocculo-oculomotor pathway from the leftcerebellum pushes the eyes to the left.

REFERENCES



3 Nystagmus


DEFINITION

Nystagmus is a rhythmic to and fro oscillation of the eyes.

GENERAL CONSIDERATIONS

The specific neurophysiologic mechanism of nystagmus is not wellunderstood. Like all eye movements, nystagmus involves all or moreof the five known supranuclear pathways1,2 namely:• Saccadic system pathway• Pursuit system pathway• Vergence system pathway• Non-optic reflex system pathway• Position maintenance system pathway.

In nystagmus, generally the movement in slow phase is in onedirection and the fast phase in the opposite direction. The fast phaseof nystagmus is mediated by the saccadic system under all conditions.One or more of the other systems mediates the slow phase. It isimportant to remember that nystagmus is given its direction based on thefast phase. This means that if we say a nystagmus is to the right, itmeans that the fast phase of the nystagmus is to the right. But actually,the important point of nystagmus is the slow phase. So actually,nystagmus should be given its direction depending on the slow phase—butthis is not done. An abnormality in the slow phase is more significant.But, alas, convention makes us talk only of the fast phase.

The eye position at any given moment results from all the impulsesfed into the III, IV and VI cranial nerve nuclei, from the supranuclearmechanism, the gaze systems and the gaze centers. Normally the inputis balanced and the eye movements are smoothly coordinated.Nystagmus develops when the normal balance is interrupted by a

Nystagmus 33

change of stimulus in a gaze system, frequently the vestibular system.Thus, in jerk nystagmus, a defect in one system results in eye deviation(slow phase) and repetitive attempts at correction of that deviation(by fast phases).

In many kinds of nystagmus, the patient has the subjectiveexperience that the world is moving or oscillopsia. Oscillopsia orperception of motion of the visual field associated with nystagmusseems to be present primarily during the slow phase of nystagmus,during which time the environment appears to move in the directionof the fast phase. You can demonstrate this for yourself by followingyour finger slowly back and forth horizontally in front of you. Noticethat the background appears to move in a direction opposite to yourslow eye movement (if the slow phase of nystagmus is to the left, thefield appears to move to the right).

During saccades (the fast phases of the nystagmus) the backgrounddoes not appear to move. Try making saccades by looking rapidlyfrom one corner of the room to the other. The background will not beperceived because of an elevated visual threshold. This elevation ofvisual threshold actually occurs prior to the start of the saccades.Some investigators believe that a discharge associated with theoculomotor activity of the saccade causes an increase of threshold inthe visual afferent system. Other evidence suggests that the elevationof visual threshold occurs in the retina as a response to the forms andcontour in the visual environment.

Environmental motion perceived during nystagmus occurspredominantly during the slow phase, but in a direction that happensto coincide with the direction of the fast phase. Consequently, a patientwith a large amplitude right-beating nystagmus (fast phase to theright) might state that the room appears to be moving to the right.During the fast phase of the nystagmus and during all saccades, visualperception is suppressed.

TERMINOLOGY

Before we proceed further we should understand what certain termsmean in nystagmus.

Pendular Nystagmus

In this there is an undulatory movement of equal speed and amplitudein both directions.


Jerky Nystagmus

Jerky nystagmus demonstrates a biphasic rhythm wherein a slowmovement in one direction is followed by a rapid saccadic return tothe original position.

Micronystagmus

Micronystagmus is a term applied to a nystagmus, which is subclinical,so that it is incapable of being detected with ordinary clinical testsbecause of its extremely small amplitude. The diagnosis is apparentby the fixation pattern, which shows a regular jerky type of nystagmuswith fast and slow phases of extremely small amplitude within theparafoveal areas so that it may be revealed only by a carefulexamination with the visuoscope or direct ophthalmoscope.

Null Zone

The field of gaze in which the intensity of nystagmus is minimal istermed the null zone.

Neutral Zone

It is that eye position in which a reversal of direction of jerkynystagmus occurs and in which any of several bidirectional waveforms,pendular nystagmus or no nystagmus may be present.

Alexander’s Law

Jerky nystagmus usually increases in amplitude with gaze in thedirection of the fast component. This is called Alexander’s law.

GRADES

Nystagmus is divided into three grades.

Grade I Jerky nystagmus is evident only in the direction of the fastphase, i.e. on conjugate deviation to one side.

Grade II When in addition, it is evident in the primary position.

Grade III When it is evident in all positions of the eyes.

EXAMINATION OF A CASE OF NYSTAGMUS

There are certain points one should check when one is examining acase of nystagmus. They are:

Nystagmus 35

• Is the nystagmus pendular or jerky?• The fast phase of the nystagmus is on which side?• Grade of nystagmus• Symptoms of nystagmus• Is squint present or not and if present, the type of squint?• Is the nystagmus affected by heads position?• Is the nystagmus worse with the eyes open or with them closed?• Is the nystagmus affected by convergence?• How wide are the ocular excursions?

CLASSIFICATION

Nystagmus can be divided into various groups (Flow chart 3.1).• Ocular nystagmus• Vestibular nystagmus• Cerebellar nystagmus• Central nystagmus• Miscellaneous.

OCULAR NYSTAGMUS

Ocular nystagmus is due to a defect or embarrassment of central vision,which renders fixation difficult or impossible. It can in turn be eitherphysiological or pathological. The physiological nystagmus can in turnbe either deviational nystagmus or optokinetic nystagmus.

Flow chart 3.1: Types of nystagmus


Deviational Nystagmus

Deviational nystagmus is also called end-point nystagmus. It is a jerkynystagmoid movement of a physiological type when the fixation ofthe axes are deviated beyond the limits of the field of binocular fixationand an effort is made to keep them there. It would generally happenif a person looks in the extreme lateral gaze. The fast phase is in thedirection of deviation. It would also occur if a person is tired or ifthere is a paresis of a muscle.

Optokinetic Nystagmus

Introduction

If a target moving in one direction is shown to a person, then the eyesmove in the direction of the target and when the target goes out ofthe limit of gaze, the eyes rapidly comes back to the center to refixatea new target. This is optokinetic nystagmus.

Clinical Test

A simple way to perform the optokinetic nystagmus (OKN) test is tohold a tailor’s tape in both our hands. One should stand one meteraway from the patient. Keep one hand stationary and with the otherhand move the tape. The patient looks at the tape. As the tape movesin one direction, the patient follows the movement of the tape by aslow eye movement (pursuit). Then there is a fast eye movement(corrective saccade) to bring back the eyes to refixate on the tape.

Kestenbaum’s Newspaper Method

The same result can be done with a sheet of a large newspaper movedslowly in front of the eyes in a direction perpendicular to the lines ofthe newspaper.

Barrie’s Ruler Test

One can use a ruler about 12 inches long to perform the OKN test.The ruler is held with its long edge horizontal and with its short edgevertical and moved to the right and left of the eye.

Optokinetic Nystagmus Drum

The best method to test OKN is to use the OKN drum. This is aspecial drum, which rotates. The drum has black and white stripespainted on it. As the drum rotates the patient fixates on the stripes.

Nystagmus 37

There is a slow phase towards the direction of movement of the drumand when the stripes go out of the field of view, the eyes have a fastphase so that they come back to the center and refixate new stripesonce again.

Pathway

Optokinetic nystagmus has two parts: a slow phase (pursuit), and afast phase (saccadic). Let us imagine a tape or target moving in frontof the patient’s eyes from left to right. When the target moves fromleft to right the eyes fixate the target and the image reaches the retina.From here it goes to the optic nerve, optic chiasma, optic tract andthen reaches the right occipital cortex in area 19 (Fig. 3.1). This areasubserves the pursuit movements. It is important to note that the

Fig. 3.1: Slow phase of optokinetic nystagmus (OKN)LR- Lateral rectus; MR- Medial rectus; LE- Left eye; RE- Right eye; Occ.lobe-Occipital lobe; Fron.lobe- Frontal lobe; III- III nerve nuclei; VI- VI nerve nuclei;PGC- Pontine gaze center; MLF- Medial longitudinal fasciculus


occipital areas mediate horizontal pursuit movements to the ipsilateralside. In other words, the right occipital lobe mediates horizontalpursuit movements to the right.

From the occipital lobe, impulses go to the same side pontine gazecenter. In this case, the impulses from the right occipital lobe go tothe right pontine gaze center. From here impulses go to the right VInerve nucleus and the left III nerve nucleus. Till here is the supranuclearpathway. From the right VI nerve nucleus and the left III nerve nucleusimpulses go via the infranuclear pathway to the lateral rectus and themedial rectus. Thus, the patient’s eyes move in the direction of thetarget.

When the moving target goes away from the field of vision theeyes which were moving slowly to that side have to come back totheir original position. A fast eye movement does this, in other wordsa saccade. This is the corrective saccade. If a stream of cars are goingin front of our vision, then we keep on following one car and when itgoes out of the field of vision our eyes would come and fixate back tothe car in the center of our field of vision. This would be done by thecorrective saccade. As the impulses from the target moving to theright reaches the occipital lobe (area 19) and the object is going out ofthe field of vision, the occipital lobe sends impulses to the ipsilateralfrontal lobe to perform the corrective saccade. In this case the rightoccipital lobe (Fig. 3.2) sends impulses to the right frontal lobe (area8). This means there has to be a communication between the occipitallobe and the frontal lobe. From the right occipital lobe impulses passto the frontal lobe via the parietal lobe.

From the right frontal lobe, impulses then pass to the left pontinegaze center which in turn sends impulses to the left VI nerve nucleusand the right III nerve nucleus. This is the supranuclear pathway.Then, the infranuclear pathway takes over and impulses got to therespective lateral and medial recti and the eyes move to the left as afast eye movement. This is the corrective saccade.

One can illustrate this with an optokinetic drum, which is a drumwith black and white stripes. The drum is rotated and the eyes fixateon it. When the stripes go away from the field of vision, the correctivesaccade occurs. This leads to a type of nystagmus known as optoki-netic nystagmus.

Parietal Lobe Lesion

If the person has a parietal lobe lesion, then there is a problem (Fig.3.3). When the corrective saccade has to work the impulse would not

Nystagmus 39

Fig. 3.2: Fast phase of optokinetic nystagmus (OKN)LR- Lateral rectus; MR- Medial rectus; LE- Left eye; RE- Right eye; Occ.lobe-Occipital lobe; III- III nerve nuclei; VI- VI nerve nuclei; PGC- Pontine gaze center;MLF- Medial longitudinal fasciculus

Fig. 3.3: Parietal lobe lesionLR- Lateral rectus; MR- Medial rectus; LE- Left eye; RE- Right eye; Occ.lobe-Occipital lobe; Fron.lobe- Frontal lobe; III- III nerve nuclei; VI- VI nerve nuclei;PGC- Pontine gaze center; MLF- Medial longitudinal fasciculus


pass beyond the parietal lobe. Thus, this would lead to a deficit in thecorrective saccade. So a deep parietal lobe lesion causes loss or decreaseof the fast phase of the OKN, when movement of the drum is towardsthe side of the lesion.

Type of OKN Abnormalities

There are four types of OKN abnormalities from type I to type IV(Table 3.1). The problems in OKN could occur if the lesion is in thepursuit system starting from the retina, optic nerve to the occipitallobe or in the saccadic system. There also could be a combination ofboth systems involved.

Inverse OKN

An inverse OKN, wherein in horizontal movements the more rapidexcursion occurs in the direction of the moving object, can be seen incases of congenital nystagmus of ocular origin or in amblyopic

Table 3.1: Types of optokinetic abnormalities

Features Type I Type II Type III Type IVSlow phase fast phase Combination complexabnormality abnormality (I and II)

Pursuit Affected Normal Affected NormalSaccade Normal Affected Normal Normal

Neuroanatomiccorrelation

Posteriorhemisphericlesions on sideof OKNabnormality

Frontomesen-cephalic lesionon side of OKNdeviation

Extensivedeephemisphericlesion on sideof SOKabnormality

Occipitallesion on sideof OKNabnormality.Disconnectionsyndromepossibleinvolvingsplenium ofthe corpuscallosum

Frequentlyassociatedsignscontralateralto lesion

Hemianopia Hemiparesis Hemianopia,Hemiparesis

Hemianopsia

Oculardeviation

Normal Eyes tonicallydeviated indirection ofmoving targets

Same astype I

Same astype I

Nystagmus 41

nystagmus. The inversion is due to the fact that a pre-existingnystagmus takes precedence over the optokinetic phenomenon andmay thus augment it or interfere with it.

Pathological Ocular Nystagmus

Amaurotic Nystagmus

Nystagmus of pendular or rarely jerky type may occur in those whohave been blind for a long time. The nystagmus is sometimes constantand at other times it appears only when the attention is aroused.

Amblyopic Nystagmus

This is due to a defect in central vision in both eyes, which precludesthe normal development of the fixation reflex.

Spasmus Nutans

In this the nystagmus occurs with head nodding. It is also called Dunkelnystagmus. It generally occurs within the first year of life. The causeappears to be difficulty in maintaining fixation, which is frequentlyassociated with inadequate light. There is also insufficient controldue to instability of the motor cortical centers in early life.

Miner’s Nystagmus

This is an acquired occupational disease of the nervous system withspecial manifestations in the ocular motor apparatus, occurring inworkers in coalmines (Fig. 3.4). Basically it is due to lack ofillumination. In the early stages which is the latent stage slightnystagmus starts. Then in the acute stage trembling of the head andhands occurs with marked nystagmus and a pathognomic attitude ofthe head being thrown back. Then the psychopathic stage starts inwhich there are cramps, tremors, headaches and insomnia. Thenystagmus is generally pendular in type in the primary position butfrequently changes to the jerky type on lateral gaze. The treatment ofthis condition is to give the patient surface work and improve thegeneral health.

Latent Nystagmus

In this condition, nystagmus is not normally present when both eyesare open but is elicited on covering either eye. In the classical case thenystagmus appears on closing one eye. Bilateral jerky nystagmus is


seen with the fast phase towards the uncovered eye. Another conditionis called manifest latent nystagmus, which occurs in patients withamblyopia or strabismus who although viewing with both eyes openare fixing monocularly. Again the fast phase is towards the directionof the intended viewing eye. The phenomenon of latent nystagmus isparticularly evident when the visual acuity of the two eyes are unequal.Sometimes if one eye has a very poor vision on covering the bettereye instead of nystagmus, a conjugate deviation of both eyes occurstowards the side of the closed eye. This is called—the latent deviationof Kestenbaum. One is not sure of the reason for latent nystagmus. Itcould be due to lack of coordination of the supranuclear centers. Itcould also be due to the fact that the nystagmus was latent but kept incheck by convergence so that abolition of the impulse to binocularconvergence allowed it to become manifest.

Fig. 3.4: Miner’s nystagmus

Nystagmus 43

VESTIBULAR NYSTAGMUS

Vestibular Apparatus

The semicircular canals are three fine tubes arranged in the ear. Thelateral semicircular canal is tilted up 30 degrees. Normally the eyes atrest are in the primary position (Fig. 3.5). Impulses go from eachsemicircular canal to the respective vestibular nuclei. From here, theimpulse goes to the opposite pontine gaze center, which in turnconnects to the same side VI nerve nucleus and opposite side III nervenucleus. The impulses thus reach the medial and lateral recti and theeyes are balanced and in the primary position.

Caloric Test

The most easily understood form of vestibular nystagmus is whenperforming the caloric test. The patient lies on a couch with the head

Fig. 3.5: Caloric test – eyes at rest in primary positionLR- Lateral rectus; MR- Medial rectus; LE- Left eye; RE- Right eye; III- III nervenuclei; VI- VI nerve nuclei; VN – Vestibular nuclei; PGC- Pontine gaze center;MLF- Medial longitudinal fasciculus


back at 60 degrees to bring the lateral semicircular canals to the verticalposition. This is because it is easier to produce convection currents ina vertical column of fluid. The test should not be performed if theeardrum is perforated. Water is taken at 30 degrees centigrade and44 degrees centigrade. Normal temperature is 37 degrees centigrade.One takes the water at 7 degrees centigrade higher and lower thanthe normal temperature. The water is run into each ear in turn. Athermostat is used to keep the temperature steady. 250 ml of water isallowed to flow over 40 seconds in the standardized test. While thewater is running the patient looks at a point straight ahead. Thisproduces vertigo and easily observed nystagmus as the canals arestimulated or inhibited and the eyes are pushed or pulled on eitherside. The duration of the nystagmus is timed. The normal duration is2 minutes and 15 seconds.

When warm water is passed in the left ear (44°C), it stimulates theleft semicircular canal. This in turn increases the discharge to the leftvestibular nucleus and thus the right pontine gaze center. This in turnleads to the eyes deviating to the right (Fig. 3.6). The slow phase of

Fig. 3.6: Caloric test with warm waterLR- Lateral rectus; MR- Medial rectus; LE- Left eye; RE- Right eye; III- III nervenuclei; VI- VI nerve nuclei; VN – Vestibular nuclei; PGC- Pontine gaze center;MLF- Medial longitudinal fasciculus

Nystagmus 45

Fig. 3.7: Caloric test with cold waterLR- Lateral rectus; MR- Medial rectus; LE- Left eye; RE- Right eye; III- III nervenuclei; VI- VI nerve nuclei; VN – Vestibular nuclei; PGC- Pontine gaze center;MLF- Medial longitudinal fasciculus

nystagmus is thus away from the ear, which is irrigated with warmwater. The eyes try to come back to the original position with a fastphase towards the left and thus a vestibular nystagmus is created.

When cold water (30°C) is passed through the left ear impulsesare inhibited in that side. So the normal right semicircular canal worksand pushes the eyes with a slow phase to the left (Fig. 3.7). The fastphase then occurs to the right.

Remember nystagmus is always talked of in regard to the fastphase. A mnemonic to remember the direction of the fast phase inthe caloric test is—COWS (cold opposite, warm same). This meanscold water calorics produce a fast phase to the opposite side andwarm water calorics produce a fast phase to the same side.

Vertical Vestibular Nystagmus

Vertical vestibular nystagmus can be elicited by bilateral caloricstimulation with the patient recumbent and his or her head flexed 30degrees above the horizontal plane. Bilateral cold water caloricsproduce vertical nystagmus with the fast phase up and the slow phase


down. Bilateral warm water calorics produce vertical nystagmus withthe fast phase down and the slow phase up. The mnemonic toremember this is: Cold Slows Things Down. This means that thecold water produces the slow phase in the downward direction.

Lesions

Vestibular nystagmus could be produced with either a central lesionor a peripheral lesion. It is very important to differentiate betweenthe two. The caloric test can differentiate between canal paresis(peripheral lesion) and directional preponderance (central lesion).

Canal Paresis (Peripheral Lesion)

If the semicircular canal or the VIII nerve are damaged an incompleteor defective response to both hot or cold water in the affected earwill be found. In a normal caloric response (Fig. 3.8) hot and coldwater produce a nystagmus for about 2 minutes. If the patient has aleft canal paresis (Fig. 3.9) then neither hot nor cold water will producea good nystagmus in the affected ear. The duration of the nystagmus

Fig. 3.8: Normal caloric response

Nystagmus 47

will be less, for example, it could be just 1 minute. In peripheral lesions,the nystagmus is unidirectional and is horizontal and not vertical. Itis enhanced by removal of ocular fixation and may be positional.

Directional Preponderance (Central Lesion)

The central connections of the vestibular nerve are such that coldwater in one ear has the same effect as hot water in the other. If it isfound that nystagmus cannot be induced to one side it indicates thatthe vestibular nucleus of the appropriate side is defective (Fig. 3.10).This is known as directional preponderance. In left directionalpreponderance both the stimuli necessary to produce nystagmus tothe right fail, that means cold in the left ear and hot in the right ear.This proves that the nerve endings are normal but the brainstemmechanism for gaze to the left is defective. Central vestibularnystagmus is bidirectional and is not influenced by removal of ocularfixation. There is likely to be associated saccadic and pursuit eyemovement disorders.

Fig. 3.9: Left canal paresis. Neither hot nor cold stimuliproduce a full effect in the left ear, i.e. local lesion


There are some situations in which both canal paresis anddirectional preponderance may be combined. This is oftenencountered when an acoustic nerve tumor or other posterior fossalesion is displacing the brainstem.

Rotational Nystagmus

Rotation of the head can also produce a rotational nystagmus. If alateral semicircular canal is stimulated, the vestibular system starts towork. If the head is rotated to the left (Fig. 3.11), the left lateralsemicircular canal is stimulated. If we tilt our head to the left, theeyes should generally keep looking straight ahead (the ultimate aimof the whole process). For the eyes to look straight ahead when wehave tilted our head to the left the eyes will move to the right. Trythis on yourself by tilting your head to the left. You will note youreyes move to the right so that you keep on looking straight ahead.

Fig. 3.10: Left directional preponderance. Both the two stimuli necessary to producenystagmus to the right fail, that means cold in the left ear and hot in the right ear.This proves that the nerve endings are normal but the brainstem mechanism forgaze to the left is defective

Nystagmus 49

When the semicircular canal is stimulated, impulse goes to the sameside (in this case left side) vestibular nucleus. From the left vestibularnucleus, impulses go to the opposite side pontine gaze center whichin turn sends impulses to the right VI nerve nuclei and left III nervenucleus. This is the supranuclear pathway. Then the infranuclearpathway takes over to the right lateral rectus and left medial rectusand the eyes turn towards the right. This constitutes the vestibularinfluence on eye movements.

On cessation of the rotation the right semicircular canal takes overproducing a deviation of the eyes to the left. Thus, the slow phase isto the left and this is the postrotational nystagmus (Fig. 3.12).Remember when we use the direction of nystagmus, it is always saidaccording to its fast phase.

Fig. 3.11: Rotational nystagmusLR- Lateral rectus; MR- Medial rectus; LE- Left eye; RE- Right eye; III- III nervenuclei; VI- VI nerve nuclei; VN – Vestibular nuclei; PGC- Pontine gaze center;MLF- Medial longitudinal fasciculus


Fig. 3.12: Postrotational nystagmusLR- Lateral rectus; MR- Medial rectus; LE- Left eye; RE- Right eye; III- III nervenuclei; VI- VI nerve nuclei; VN – Vestibular nuclei; PGC- Pontine gaze center;MLF- Medial longitudinal fasciculus

Doll’s Head Phenomenon

The rotational nystagmus provides a simple method for testingvestibular responses in an infant or comatose patient. If an infant orcomatose patient is held at arm’s length and the head tilted slightlytowards the examiner and rotated to the patient’s left, the infant willdevelop a slow tonic deviation to the right and a corrective saccadeto the left. This is the doll’s head phenomenon. This is extremelyhelpful in confirming the diagnosis of congenital oculomotor apraxiain infants. In this disorder, the saccadic mechanism is defective. Duringrotation of the head, the child will have the slow phase movement ofthe eyes opposite the direction of rotation of the head, but the eyeswill not have a fast phase saccadic return.

If you are not able to perform the caloric test in your office, youcould ask the adult patient to spin around several times while you

Nystagmus 51

note the postrotational nystagmus when the spinning is stopped. Thenormal patient who is spun to the left will develop postrotationalnystagmus to the right once the spinning is stopped. In other wordsthe slow phase will be towards the left and the fast phase towardsthe right. The environment will appear to move in the direction ofthe fast phase.

CEREBELLAR NYSTAGMUS

The exact mechanism of cerebellar nystagmus is not known. Whennystagmus occurs it is opposite that found in a vestibular lesion. In aright-sided vestibular lesion, the slow phase of the nystagmus is tothe right and the fast phase to the left. This means the nystagmus is tothe left, in other words opposite the side of the lesion. In cerebellardisease, the fast phase of the nystagmus is on the same side of thelesion. So, if there is a right sided-cerebellar lesion, the fast phase ofthe nystagmus is towards the right side. This could be due to theflocculo-oculomotor pathway, which works in the reverse of thevestibular pathway. The left vestibular pathway pushes the eyes tothe right whereas the left flocculo-oculomotor pathway from the leftcerebellum pushes the eyes to the left.

CENTRAL NYSTAGMUS

In central nystagmus, the nystagmus is of the jerky type. It isoccasionally present when the eyes are at rest, but usually developsonly when they are deviated to one or the other direction. Thenystagmus is symmetrical. This means that the movement starts atthe same angle of eccentricity and has approximately the sameexcursion whether the gaze is directed to one or the other side.

MISCELLANEOUS

Voluntary Nystagmus

Voluntary nystagmus is habit learned and retained. The movementsare pendular and minute and in a horizontal direction.

Hysterical Nystagmus

Hysterical nystagmus is just like voluntary nystagmus but theoscillations are quicker.


Idiopathic Congenital Nystagmus

In this there is congenital nystagmus without any known cause. Thisincludes all forms of nystagmus noted at birth or within the prenatalperiod. It is usually horizontal but may be vertical, circular or elliptical.It may be pendular or jerky. Certain important points about congenitalnystagmus are:• It is binocular and there is similar amplitude in both eyes• There is no oscillopsia and it is abolished in sleep• It is dampened by convergence and increased by a fixation effort.

As it is dampened by convergence the child usually has good nearacuity and can do well in school

• It is uniplanar. This is the hallmark of congenital nystagmus. Planeof the nystagmus, usually horizontal remains unchanged in allpositions of gaze including the vertical gaze. This phenomenon isseen only in three entities—congenital nystagmus, peripheralvestibular nystagmus and periodic alternating nystagmus

• One can frequently identify a null zone of gaze in which thenystagmus is least marked and the visual acuity is the best

• The patient may manifest a head turn to keep the eyes in the nullzone or alternatively have a muscle surgery to create the sameeffect

• High astigmatism is frequently found which can be treated bycontact lenses.

Nystagmus Blockage Syndrome

In this there is reduction of nystagmus or blockage of the nystagmusin some particular gaze. The nystagmus diminishes or disappears withthe willed act of forced convergence while fixating a distant target.This should not be confused with the dampening of congenitalnystagmus during convergence on a near target.

SYMPTOMS

The various symptoms of nystagmus are oscillopsia, diplopia, tiltingof the head or head nodding.

TREATMENT

The treatment can be treating the cause, use of prisms or surgery inwhich Faden’s operation is done. The methods to treat nystagmusare shown in flow chart 3.2. The treatment can be general treatmentwhere the cause is treated or specific treatment, which can be medical

Nystagmus 53

or surgical. In medical treatment one can improve the visual acuity byusing prisms base out to simulate fusional convergence. One can useprisms to eliminate anomalous head postures also. For a head turn tothe left, the neutral zone is in dextroversion and a prism base outbefore the right eye and base in before the left eye will shift the eyesconjugately along with the neutral zone towards the primary position.One can also use occlusion in which partial occlusion of the sound eyewith a neutral density filter to decrease visual acuity in the fixatingeye to a level below that of the amblyopic eye but not dark enough toelicit the nystagmus is used. Surgically one can perform Faden’soperation in which the required muscle creating the nystagmus issutured to the sclera at the equator.

REFERENCES



Flow chart 3.2: Treatment of nystagmus

4 The Pupil


NORMAL PUPIL

The pupil is an aperture present in the center of the iris and controlsthe amount of light entering the eye and reaching the retina. There isgenerally only one pupil but in some cases one can have more thanone pupil and this condition is called polycoria.

PUPILLARY PATHWAYS

Introduction

When light is shone in one eye, both the pupils constrict.1,2 Constrictionof the pupil to which light is shone is called direct light reflex and thatof the other pupil is called consensual (indirect) light reflex. If both pupilsare illuminated simultaneously, the response summates. This meansthe constriction of each pupil is greater than the constriction notedwhen only one pupil is illuminated. Rods and cones initiate the lightreflex.

Pupilloconstrictor Light Reflex Pathway

Afferent

The outer segments of the rods and cones are the receptors for boththe visual pathway and the light reflex. When light is flashed on theeyes, the pupillary fibers run in the optic nerve. From there they crossin the optic chiasma and reach the optic tract (Fig. 4.1). From the optictract they leave the visual pathway fibers (which continue to the lateralgeniculate body) and reach the pretectal nucleus. This is an ill-definedcollection of small cells anterior to the lateral margin of the superiorcolliculus. Internuncial fibers connect each pretectal nucleus with the

The Pupil 55

Edinger-Westphal nucleus of both sides. Half of the postsynaptic fibersfrom the pretectal area curve around the periaqueductal gray matterto terminate in the ipsilateral Edinger-Westphal nucleus, while theother half cross, mainly via the posterior commissure to thecontralateral Edinger-Westphal nucleus. This connection forms thebasis of the consensual light reflex. Any given pretectal neuron behavesfunctionally as though it receives similar inputs from each eye andprojects equally in each Edinger-Westphal nucleus.

Efferent

Preganglionic parasympathetic myelinated fibers now go to the ciliaryganglion via the third cranial nerve. They leave the III nerve in itsbranch to the inferior oblique. After reaching the ciliary ganglion theysynapse there. Then postganglionic myelinated fibers pass through

Fig. 4.1: Pupilloconstrictor light reflex pathway


the short ciliary nerves to innervate the sphincter pupillae. Normally,postganglionic fibers are non-myelinated and this is the only exceptionto this rule. These are the parasympathetic fibers.

Sleep Normally, there is a tonic inhibitory input from the cerebralcortex to the Edinger-Westphal nucleus and it is a diminution of thisinput that results in pupillary constriction during sleep.

Functions of the Light Reflex

• Pupillary constriction associated with light reflex protects againstexcessive bleaching of the visual pigments by reducing the amountof light entering the eye.

• Light reflex helps in light and dark adaptation. This plays a role inmaximizing visual acuity at different light levels. A large pupilwill allow more light and so can allow greater acuity in dimillumination. On the other hand, a smaller pupil will limit the aberra-tions produced by the eye’s refractive system and so can also allowgreater acuity. It has been found that at any given light level, thesize of the pupil strikes an optimum balance between these twofactors.

Convergence Near Reflex Pathway

Near reflex occurs on looking at a near object. It consists of twocomponents—a convergence reflex and an accommodation reflex. Theconvergence reflex comprises convergence of the visual axes of theeyes with associated constriction of the pupil.

Afferent

The afferent starts from the medial recti. This travels centrally via thethird nerve to the mesencephalic nucleus of the fifth nerve. Fromhere the impulses travel to the convergence center in the tectal orpretectal region. Internuncial fibers from the convergence center thengo to the Edinger-Westphal nucleus (Fig. 4.2).

Efferent

The efferent pathway is along the third nerve (similar to that of thelight reflex). From the III nerve efferent fibers of convergence reflexrelay in the accessory ciliary ganglion and from there reach thesphincter pupillae.

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Accommodation Reflex Pathway

The accommodation reflex consists of increased accommodation andassociated constriction of the pupil.

Afferent

The afferent starts from the retina. Impulses go from the rods andcones to the optic nerve, optic chiasma and optic tract (Fig. 4.3). Fibersthen pass to the lateral geniculate body, optic radiation’s and striatecortex. The impulses reach area 19 of the occipital cortex. Internuncialfibers then pass from area 19 to the pontine center via theoccipitomesencephalic tract. From the pontine center fibers pass tothe Edinger-Westphal nucleus of both sides.

Fig. 4.2: Convergence reflex pathway


Efferent

From the Edinger-Westphal nucleus the efferent impulses travel alongthe III cranial nerve and relay in the ciliary and accessory ciliaryganglion. From there the fibers reach the sphincter pupillae.

Pupillary Dilatation Pathway

The pupillary dilatation starts from the posterior hypothalamus (Fig.4.4). The pathway is the sympathetic pathway unlike thepupilloconstrictor pathway which is parasympathetic. From thehypothalamus first-order neurons start which reach the ciliospinalcenter of Budge. These fibers descend uncrossed. This center is locatedin the intermediolateral cell column of C8, T1 and T2.

The second-order neuron starts from the ciliospinal center of Budge.These are the preganglionic fibers and they travel via the inferior andmiddle cervical ganglion to synapse in the superior cervical ganglion.During this long course the preganglionic fibers are closely related tothe apical pleura where they may be damaged by bronchial carcinoma.This is Pancoast’s tumor. They can also be damaged during surgeryon the neck.

Fig. 4.3: Accommodation reflex pathway

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The third-order neurons are postganglionic neurons which arisefrom the superior cervical ganglion. They ascend along the sympatheticplexus around the internal carotid artery to enter the skull. The fibersthen join the sympathetic plexus around the ophthalmic artery. Thenthey go to the nasociliary nerve (branch of ophthalmic division of thetrigeminal nerve) and pass through the ciliary ganglion. They do notsynapse in the ciliary ganglion and reach the dilator pupillae via thelong ciliary nerves.

Darkness Reflex

When a person goes from a lighted environment to darkness, thepupils dilate. This dilatation has two causes: the first is simply abolitionof light reflex with consequent relaxation of the sphincter pupillae,and the second is contraction of the dilator pupillae supplied by thesympathetic nervous system. The pathways involved in dark reflex

Fig. 4.4: Pupillary dilatation pathway


are presumably the same as those of light reflex, since the dilatationat the end of long light stimulation also involves both relaxation ofthe sphincter pupillae and contraction of the dilator pupillae.

Psychosensory Reflex

Psychosensory reflex refers to dilatation of the pupil in response tosensory and psychic stimuli. A large number of differently describedreflexes fall into this category. They are not seen in a newborn baby,but appear in the first few days of life, developing fully at the age ofsix months. Their mechanism is very complex and their pathwayshave still not been elucidated. It is believed that the mechanism ofpsychosensory reflexes is a cortical one and the pupillary dilatationresults from two components—a sympathetic discharge to the dilatorpupillae and an inhibition of the parasympathetic discharge to thesphincter pupillae.

PUPIL CYCLE TIME

A small beam of light focussed at the pupillary margin induces regular,persistent oscillations of the pupil. These oscillations can be timedwith a stopwatch. The period of the average complete cycle is calledthe pupil cycle time. It is prolonged in optic neuritis and in compressiveoptic neuropathy.

LESIONS OF THE PUPIL

There are various lesions, which can occur in the pupil (Fig. 4.5)depending upon the location of the lesion. They are as follows:

Amaurotic Pupil

Amaurotic pupil is a total afferent pupillary defect (Fig. 4.5). A completeoptic nerve or retinal lesion leading to total blindness on the affectedside causes it. The eye has no perception of light. The points in anamaurotic pupil are:• The pupil neither reacts to direct light stimulation, nor does it

create a consensual light reflex in the opposite eye• When light is shone on the opposite eye, there is a good light

reflex in that eye and a good consensual light reflex in the affectedeye

• This shows that the defect is an afferent defect and the efferentsystem is normal.

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Marcus Gunn Pupil

Swinging Flashlight Test

A Marcus Gunn pupil is a relative afferent pupillary defect. Anincomplete optic nerve lesion or severe retinal disease causes it. It isbest tested by the swinging flash-light test. To perform this test (Fig.4.6), a bright flashlight is shone onto one pupil and constriction isnoted. Then the flashlight is quickly moved to the contralateral pupiland the response is noted. This swinging to and fro of the flashlightis repeated several times while the pupillary response is observed.Normally, both pupils constrict equally and the pupil to whom lightis transferred remains tightly constricted. In the presence of a relativeafferent pupillary defect in one eye, the affected pupil will dilate whenthe flashlight is moved from the normal eye to the abnormal eye.

Fig. 4.5: Lesions of the pupil


This is a paradoxical response. This is called the Marcus Gunn pupiland is the earliest indicator of optic nerve disease even in the presenceof a normal visual acuity.

Grades

Marcus Gunn pupil can be graded depending on the response to theswinging flashlight test. During the swinging flashlight test, if theamount of light information transmitted from one eye is less thanthat carried from the fellow eye, the following phenomenon may benoted when the light is swung from the normal eye to the defectiveeye. Thus Marcus Gunn pupils can be graded.• 3-4 + Marcus Gunn pupil: There is immediate dilatation of the pupil,

instead of normal initial constriction• 1-2 + Marcus Gunn pupil: No change in pupil size, initially, followed

by dilatation of the pupils• Trace Marcus Gunn pupil: Initial constriction, but greater escape to

a larger intermediate size than when the light is swung back to thenormal eye.

Fig. 4.6: Swinging flashlight test

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Lesion

Marcus Gunn pupil sign indicates an asymmetry of conduction andwill not be present in symmetric bilateral lesions of the optic nerve orretinal disease. A Marcus Gunn pupil will not occur if the lesion is inthe optic chiasma or optic tract as in these areas fibers are presentfrom the opposite eye also.

Important Points

• There is no such thing as bilateral Marcus Gunn pupil. There maybe bilaterally reduced direct response of the pupils to light,resulting in light-near dissociation, but the Marcus Gunnphenomenon requires asymmetry of the afferent light transmission.

• Opacities of the ocular media (corneal scar, cataracts or vitreoushemorrhage) will not cause a Marcus Gunn pupillary phenomenonif a strong enough flashlight is used.

• Extensive retinal damage will cause a significant Marcus Gunnphenomenon.

Wernicke’s Hemianopic Pupil

Wernicke’s hemianopic pupil indicates the lesion in the optic tract(Fig. 4.5). In this condition, light reflex is absent when light is thrownon the temporal half of the retina of the affected side and nasal half ofthe retina of the opposite side. Light reflex is present when the lightis thrown on the nasal half of the affected side and temporal half ofthe opposite side. The patient also has homonymous hemianopia asthe lesion is in the optic tract.

Argyll Robertson Pupil

Lesion

A lesion (neurosyphilis) causes it in the region of tectum (Fig. 4.5).The lesion is in the region of the sylvian aqueduct when the fibersfrom the pretectal nucleus go to the Edinger-Westphal nucleus. AnArgyll Robertson pupil occurs when in addition to involvement ofthe internuncial neurons, there is a disturbance of the normal inhibitorypathways from the reticular activating system upon theparasympathetic Edinger-Westphal subnucleus. The result of thisinhibition is excessive parasympathetic activity and small pupils.


Features

• The vision in the affected eye is normal• There is no reaction to light• The near reflex is normal and the pupils react as the convergence

and accommodation reflex fibers are not affected. The fibers thatmediate the pupillary near response lie ventral to the internuncialneurons that enter the Edinger-Westphal nucleus

• The pupils are miotic and irregular• The pupils dilate very poorly with mydriatics.

Light-Near Dissociation

There are many causes of light-near dissociation. They are shown in Figure4.5. They are:• Argyll Robertson pupil• Bilateral complete afferent pupillary defect as in bilateral optic

atrophy. In these the convergence reflex pathway (Fig. 4.2) is notaffected as it starts from the medial recti, so there is a light-neardissociation

• Lesions in the pretectal area as once again the near reflex are notaffected. This occurs in Parinaud’s syndrome.

Pseudo-Argyll Robertson Pupil

In this there is third nerve palsy with aberrant regeneration of medialrectus innervation into the sphincter innervation pathway.

How to Test for a Pupillary Near Response

The near response should be tested in good room light so that thepatient’s pupils are midsized and the near object is clearly visible.The patient is given an accommodative target to look at. Watchingfor convergence helps the examiner judge how hard the patient istrying.

Tonic Pupil

Damage to the ciliary ganglion or short ciliary nerves (Fig. 4.5) produces thetonic pupil. The features are:• Reaction to light is absent and to near reflex very slow and tonic• Accommodative paresis is present• The affected pupil is larger• It is generally unilateral

The Pupil 65

• Cholinergic supersensitivity of the denervated muscle occurs. Thenormal pupil does not constrict with 0.125 percent pilocarpinewhereas the tonic pupil does.It could be due to viral infections affecting the ciliary ganglion like

herpes zoster. It could also be due to diabetes or alcoholism.When a tonic pupil is associated with absent deep tendon reflexes

in the lower extremities the condition is called Adie’s tonic pupil. Thelesion is due to denervation of the postganglionic supply of thesphincter pupillae and ciliary muscle of unknown etiology. It generallyoccurs in women.

The near response of the pupil generally exceeds the light reactionin Adie’s syndrome. The near response is slow and steady and onlooking back into the distance it tends to hold the contraction for afew seconds. Thus it is tonic. The reasons for this behavior are notvery well understood. The slowness of the tonic pupil might be dueto the diffusion of acetylcholine through the aqueous to thesupersensitive receptors of the iris sphincter. The near reaction is notspared in Adie’s syndrome—it is restored. Aberrant regeneration offibers occurs that were originally destined for the ciliary muscle intothe iris sphincter. So with every effort to focus the eye on a nearobject, impulses spill into the sphincter, constricting the pupil.Accommodative fibers in the short ciliary nerves outnumber sphincterfibers by 30 to 1. This means that the ciliary muscle will probablyreceive appropriate reinnervation, but the odds against the irissphincter receiving the right fibers are very high. Thus with randomregeneration of fibers the power of accommodation is likely torecover, whereas the light reaction will not. At the same time thesphincter is likely to be served by aberrant accommodative impulsesthat constrict the pupil firmly with every near effort.

Hutchinson’s Pupil

Hutchinson’s pupil occurs in comatose patients with unilaterallydilated, poorly reactive pupils. It is due to ipsilateral, expandingintracranial supratentorial mass (tumor or subdural hematoma) thatis causing downward displacement of the hippocampal gyrus anduncal herniation across the tentorial edge with entrapment of the thirdnerve. The pupillomotor fibers travel in the peripheral portion of thethird nerve and are subject to early damage from compression. Thisabnormality typically heralds the onset of a III nerve paralysis and isan internal ophthalmoplegia. The appearance of an internalophthalmoplegia in a patient with a suspected or proven supratentorialmass is an ominous sign and indicates urgent surgical intervention.


Horner’s Syndrome

Introduction

In Horner’s syndrome there is a lesion of the sympathetic system.There can be three types—central, preganglionic or postganglionic(Fig. 4.7). The characteristic features are as follows.

Ptosis There is mild to moderate ptosis due to paralysis of theMuller’s muscle which is supplied by the sympathetic system.

Enophthalmos There can be upside down ptosis also and this is dueto weakness of the inferior tarsal muscle. In this there is elevation ofthe inferior eyelid. This leads to an apparent enophthalmos.

Miosis There is moderate miosis due to unopposed action of thesphincter pupillae following paralysis of the dilator pathway. Pupillaryreactions are normal to light and near. When the lights are turned offthe Horner’s pupil dilates more slowly than the normal pupil becauseit lacks the pull of the dilator pupillae. This is called dilatation lag.

Fig. 4.7: Horner’s syndrome

The Pupil 67

Facial anhydrosis Reduced sweating on the ipsilateral face and neckoccurs. This is characteristic of preganglionic Horner’s syndrome.

Heterochromia iridis When the sympathetic ocular innervation isinterrupted early in life (congenital Horner’s syndrome) the pigmentof the iris stroma fails to develop producing heterochromia iridis.

Central Horner’s SyndromeThis occurs in lesions located between the hypothalamus and theciliospinal center of Budge (Fig. 4.7). It is due to brainstem vascularlesions or demyelinating lesions. The patient will also have brainstemsigns and sudden onset of vertigo.

Preganglionic Horner’s Syndrome

In this the lesion is located from C8 toT2 and the superior cervicalganglion. In other words, the second-order neurons are affected. Thiscan occur in Pancoast’s tumor of the lung or surgery in the neck.There is anhidrosis of the face and neck as the fibers for sweatingcome out from the superior cervical ganglion.

Postganglionic Horner’s Syndrome

The lesion involves the third-order neurons from the superior cervicalganglion to the dilator pupillae. It can occur in cavernous sinus lesionsor head trauma. There is ipsilateral vascular headache.

Pharmacological Tests for Horner’s Syndrome

Cocaine test When 4 percent cocaine is instilled in both eyes, the normalpupil will dilate but the Horner’s pupil will not (Fig. 4.8). All Horner’spupils, no matter where the defect in the pathway is located, willdilate poorly to cocaine. Thus, cocaine helps in establishing thediagnosis of sympathetic denervation and not in localizing the site oflesion.

Hydroxyamphetamine test When 10 percent drops of this drug areinstilled into both eyes, in a patient with preganglionic lesion bothpupils will dilate whereas in postganglionic lesions, the Horner’s pupilwill not. It is because, since the hydroxyamphetamine acts by releasingnorepinephrine from the nerve endings at the myoneural junction, soin postganglionic lesions, the drug will have no effect.

Adrenaline test or phenylephrine test When either adrenaline 1 in 1000or phenylephrine 10 percent is instilled in both eyes, the Horner’spupil due to postganglionic lesion dilates more than the normal pupilbecause of denervation hypersensitivity.


Reader’s Syndrome

This applies to painful postganglionic Horner’s syndrome. Clusterheadaches are present. Raeder’s paratrigeminal syndrome is a termthat should probably be limited to the occasional middle fossa massthat produces trigeminal nerve involvement with pain and apostganglionic Horner’s syndrome.

PHARMACOLOGY OF THE PUPIL

The iris has a sphincter controlled by the parasympathetic system(Fig. 4.9) and a dilator controlled by the sympathetic system (Fig.4.10). In both the systems acetylcholine is the neurotransmitter at thesynapse between the preganglionic and postganglionic neurons. Inthe parasympathetic system, acetylcholine is the neuroeffector at thesphincter. In the sympathetic system the neuroeffector at the dilator

Fig. 4.8: Pharmacological tests to localize Horner’s syndrome

The Pupil 69

Fig. 4.9: Parasympathetic system

Fig. 4.10: Sympathetic system


is norepinephrine. There are alpha- and beta-sympathetic receptorsin the ciliary body. The beta-receptors are inhibitory. Norepinephrineacts only upon alpha-receptors, which are the only receptors presentin the dilator muscle of the iris. An iris deprived of postganglionicinnervation develops supersensitivity within 24 to 48 hours, i.e. aphysiologic response occurs when lesser amounts of cholinergic andsympathetic substances are present than those usually required tocause the same physiologic response.

Parasympathetic drugs can be of three types: (i) the directly actingdrugs like pilocarpine which act directly on the effector and have thesame action as the acetylcholine, (ii) indirect-acting cholinergic agentsthat interfere with the hydrolysis and degradation of acetylcholine,for example, the anticholinesterase inhibitors like eserine andphysostigmine, and (iii) anticholinergic drugs that compete withacetylcholine for receptors at the effector site of the sphincter muscle,such as atropine. Atropine blocks the parasympathetic receptors atthe sphincter muscle and prevents the muscle constriction caused byacetylcholine.

Sometimes, one has to find out whether a fixed dilated pupil (Fig.4.11) is due to an interruption of parasympathetic innervation by ananatomic lesion or to pharmacological dilatation of the pupil. Theexaminer should instill 1 to 2 percent pilocarpine in the affected eye.

Fig. 4.11: Dilated pupil

The Pupil 71

If the patient has received an anticholinergic drug that dilated thepupil by blocking the receptor site, the pupil will not constrict. If thepupillary dilatation is due to interruption of the parasympatheticpathways proximal to the neuroeffector junction, the pilocarpine willact directly on the sphincter muscle and will cause pupillaryconstriction.

Sympathetic acting drugs can be directly acting or indirectly actingdrugs. The directly acting drugs like phenylephrine or epinephrineact directly on the alpha-receptors dilating the pupil. The indirectlyacting drugs like cocaine and hydroxyamphetamine (Paredrine) actin a different way. Cocaine causes pupillary dilatation by blockingthe normal re-uptake of constantly released norepinephrine. This leadsto an accumulation of norepinephrine at the neuroeffector junction.Hydroxyamphetamine acts directly on the neuroeffector junction andcauses release of norepinephrine from presynaptic vesicles. Thepresence of norepinephrine in presynaptic vesicles depends on theintegrity of the third-order neuron. The presence of norepinephrinein these vesicles is not impaired by interruption of the preganglionic(second-order) neuron.

PUPIL ABNORMALITIES

Hippus

Hippus is a visible rhythmic but irregular pupillary oscillation,deliberate in time and 2 mm or more in excursion. It has no localizingsignificance. It occurs in:• Normal person• Presence of total third nerve palsy• Hemiplegia• Multiple sclerosis• Meningitis (acute)• Cerebral syphilis• Myasthenia gravis• Epileptics.

Paradoxical Pupillary Reaction

In this either: (i) the pupil dilates with near vision or constricts indistant vision, or (ii) the pupil dilates on exposure to light or constrictswhen the light is withdrawn. It occurs in:• Syphilis• Tumors of quadrigeminal region


• Sleeping individuals who have taken barbiturates• Trauma.

Irregularity of the Pupil

Irregularity of the pupil occurs in:• Congenital coloboma of the iris• Operations on the iris—like sector iridectomies• Adherent leukoma as one part of the iris is pulled up to the corneal

scar• Peripheral anterior synechiae• Iritis• Glaucoma• Tumors of the iris or ciliary body• Argyll Robertson pupil• Iridocorneal endothelial syndrome• Optic atrophy.

Polycoria

In this there are more than one pupils present. It occurs in:• Congenital• Surgical—due to a surgical iridectomy• Iridocorneal endothelial syndrome (essential iris atrophy)• Iridoschisis.

REFERENCES



5Visual Pathway

Athiya Agarwal

INTRODUCTION

The visual pathway starts from the retina and ends in the corticalareas.1,2 There are basically seven levels through which the visualimpulses pass. They are: (i) retina, (ii) optic nerve, (iii) optic chiasma,(iv) optic tract, (v) lateral geniculate body, (vi) optic radiation, and(vii) cortical areas.

Retina

The end organ of the visual pathway is the neural epithelium of therods and cones. The first conducting nerve cell or neuron of the firstorder is the bipolar cell. From the bipolar cells the impulses travel tothe ganglion cells (Fig. 5.1). From the ganglion cells to the lateralgeniculate body (LGB) is the second-order neuron and from the LGBto the occipital cortex is the third-order neuron. This is done via theoptic radiations. In the optic nerve head the peripheral fibers fromthe retina insert in the periphery of the disk and those from the centralretina insert in the center of the disk (Fig. 5.2).

Optic Nerve

The optic nerve is the second cranial nerve and is about 5 cm in length.It has basically 4 portions (read Chapter 6 on Anatomy of the OpticNerve). They are:• Intraocular portion• Intraorbital portion• Intracanalicular portion• Intracranial portion.


Fig. 5.1: Neurons in the visual pathway

Fig. 5.2: Arrangement of nerve fibers in the disk from the retina. The peripheralfibers insert in the periphery of the disk while the central fibers insert in the centerof the disk

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Optic Chiasma

Definition

Optic chiasma is a commissure formed by the junction of the opticnerve. This provides for crossing of the nasal retinal fibers to theoptic tract of the opposite side and for passage of temporal fibers intothe optic tract of the ipsilateral side.

Dimensions

It is a flattened oblong band, some 12 mm in its transverse diameterand 8 mm from before backwards.

Types

Central chiasma This is present in about 80 percent of cases. It liesdirectly (Fig. 5.3) above the sella, so that expanding pituitary tumorswill involve the chiasma first.

Fig. 5.3: Variations of optic chiasma


Prefixed chiasma This is seen in about 10 percent of cases. In thesecases, the chiasma is present more anteriorly over the tuberculumsellae. In such a situation, the pituitary tumor may involve the optictracts first.

Postfixed chiasma This is seen in about 10 percent of cases. In thesecases, the chiasma is located more posteriorly over the dorsum sellaeso that pituitary tumors are apt to damage the optic nerve first.

Anatomy

The optic chiasma lies over the (Fig. 5.4) the diaphragma sellae and isensheathed in pia surrounded by cerebrospinal fluid. As it lies overthe diaphragma sellae, presence of a visual field defect in a patientwith a pituitary tumor indicates suprasellar extension. Posteriorly,the chiasma is continuous with the optic tracts.

Relations

The relations of the optic chiasma (Figs 5.4 and 5.5) are:Anteriorly—are the anterior cerebral artery and their anterior

communicating branch.Laterally—is the internal carotid artery, as it passes upwards after

having pierced the roof of the cavernous sinus. It lies on each side incontact with the chiasma in the angle between the optic nerve andtract. Laterally too is the anterior perforated substance. The medialroot of the olfactory tract lies laterally.

Fig. 5.4: Anatomy of the optic chiasma

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Posteriorly—is the tuber cinereum—a hollow elevation of graymatter situated between the mamillaria bodies behind and the opticchiasma in front. Laterally, it is continuous with the gray matter ofthe anterior perforated substance. From its inferior aspect theinfundibulum, which is a hollow conical process, passes downwardsand forwards and through a hole in the posterior part of thediaphragma sellae attaches itself to the posterior lobe of the pituitarygland. The infundibulum is thus in close contact with theposteroinferior part of the chiasma, which it joins at an acute angle.

Above—is the third ventricle, in the floor of which the chiasmamakes a prominence.

Inferior—is the hypophysis (pituitary gland) and under the lateraledge of the chiasma is the cavernous sinus.

Optic Tract

Definition

Each optic tract is a cylindrical band, which runs from the optic chiasmato the crus cerebri.

Fig. 5.5: Relations of optic chiasma


Course

It runs laterally and backwards from the posterolateral angle of thechiasma between the tuber cinereum (Fig. 5.5) and the anteriorperforated substance. Becoming more flattened and strap-like it isunited to the upper part of the anterior then lateral surface of thecerebral peduncle (crus cerebri).

Relations

The course can be divided into three parts:Anterior part In the first section of its course (Fig. 5.5), the optic

tract lies superficial on the under aspect of the brain. It runs abovethe dorsum sellae and crosses the third nerve from medial to lateral.Above is the posterior part of the anterior perforated substance andthe floor of the third ventricle while medially is the tuber cinereum.

Middle part In the middle region of its course, the optic tract lieshidden between the uncus and the cerebral peduncle (crus cerebri). Itis here also the flattening commences to conform to the upper aspectof the uncus. The optic tract here crosses the pyramidal tract, which occupiesthe middle segment of the basis pedunculi. Nearby, just dorsal to the substantianigra, are the lemnisci carrying sensory fibers. It thus comes about that asingle lesion here can affect vision and also the great motor and sensory roots.

Posterior part In the posterior part of its course, the optic tract liesin the depths of the hippocampal sulcus. Below and parallel to it runsthe posterior cerebral artery.

Roots

In the posterior part of its course, the optic tract divides into tworoots—the medial root and the lateral root.

Medial root The medial root passes to the medial geniculate body.These are not light fibers but commissural auditory fibers betweenthe two medial geniculate bodies, whose course in the white matteris via the optic tracts and chiasma. It is called the Gudden’scommissure.

Lateral root This spreads over the LGB and for the most part endsin it.

Terminations

The fibers of the optic tract coming from the ganglion cells of theretina reach three major destinations. They are:• Lateral geniculate body—for relay to the visual cortex

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• Each pretectal nucleus—as part of the pupilloconstrictor pathway• Superior colliculus—for general reflex responses to light.

Lateral Geniculate Body

Definition

Lateral geniculate bodies (LGBs) are a pair of bodies, which are partof the thalamus and form an end station for all fibers subservingvision in the optic tracts.

Shape

Oval or cap-like structure.

Situation

On the posterior aspect of the thalamus.

Development

During the process of development from lower forms of life, there isa lateral rotation of the LGB as well as changes in its structure. As aresult, in man, the original external surface has become ventral. Thisis of importance as regards the disposition of retinal fibers in theLGB.

Parts

The LGB is an asymmetrical cone, with a rounded apex to its mainbulk or body and an incomplete rim inferiorly. The rim is drawn outlaterally as a peak or spur, which is largely responsible for the surfaceelevation known as the LGB. The anterior part of the rim is observedby the entry of the optic tract (Fig. 5.6). The medial part of the rim issuperior to the medial root and is variably responsible for the surfaceelevation, which appears to lead dorsally into the medial geniculatebody. Inferiorly, the nucleus is hollowed; producing a kind of hilum,which also extends onto the dorsal aspect of the nucleus which here,has no rim. The hilum may be represented by a superficial cleft ordepression.

Relations

On coronal section It appears like a peaked cap, the peak projectinglaterally.


On horizontal section It is shown to be related anteriorly with theoptic tract which ends therein. Laterally (Fig. 5.7), it is related to theretrolenticular portion of the internal capsule. Medially it is relatedto the medial geniculate body, posteriorly with the hippocampalconvolution and posterolaterally with the inferior horn of the lateralventricle.

On sagittal section It is seen that the fibers of the optic tract divideinto two layers: the inferior of these forms the white layer of thehilum; and the superior forms the dorsal portion of the saddle. Betweenthese laminae which form the capsule of the LGB are alternating layersof myelinated fibers and cells which give the body its characteristicappearance. From the dorsal portion of the LGB pass a mass of fibers(which form its peduncle) into the area of Wernicke. This is a smallregion of myelinated fibers enclosed by the thalamus medially, theinternal capsule laterally and the LGB posteriorly. The mainconstituents of the area of Wernicke are the fibers of the opticradiation. It also contains the vertical temporothalamic fibers of Arnold.

Superior Brachium

The LGB is connected to the superior colliculus by a slender bandcalled the superior brachium.

Fig. 5.6: Anatomy of the lateral geniculate body (LGB)

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Optic Radiations

Definition

Optic radiation or optic radiation of Gratiolet is a fresh relay of fibersthat carry the visual impulses from the LGB to the occipital lobe.

Course

They pass forwards and then laterally through the area of Wernickeas the optic peduncle, anterior to the lateral ventricle and traversingthe retrolenticular part of the internal capsule behind the sensoryfibers and medial to the auditory tract. The fibers spread out fanwiseto form the medullary optic lamina.

Meyer’s Loop

The ventral portion of the optic radiation instead of sweeping backinto the occipital lobe plunges forwards into the temporal pole beforepassing backwards as an inferior longitudinal fasciculus of Meyer.This is known as Meyer’s loop (Fig. 5.8). Interference with this loopcauses a superior homonymous quadrantic hemianopia.

Fig. 5.7: Relations of the lateral geniculate body


Further Course

The optic radiations as they pass back into the white matter of thecerebral hemisphere lie deep to the middle temporal gyrus, so thattumors of this portion of the temporal lobe may give rise to visualdefects. The optic radiations end in the occipital lobe in an extensivearea of thin cortex in which is the white stria of Gennari.

Other Fibers

The other fibers in the optic radiations are:• Fibers that pass from the cortex to the LGB and the superior

colliculus• Descending nerve fibers passing to the ocular motor nuclei.

The Visual Cortex

Calcarine Sulcus

In man, the visual projection cortex is situated along the superior andinferior lips of the calcarine sulcus (Fig. 5.9). This area is usually calledthe striate cortex because of the prominent band of geniculocalcarinefibers termed as striae of Gennari, after its discoverer who discoveredit in 1776. The striate cortex is also referred to as area 17 of Brodman.The anterior part of the sulcus is called the calcarine fissure and theposterior part is called the postcalcarine fissure. The striate cortex issituated on the inferior and superior lips of the postcalcarine fissureand on the inferior lips of the calcarine fissure.

Fig. 5.8: Optic radiations and Meyer’s loop

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Course of calcarine sulcus The calcarine sulcus is a deep sulcusextending from near the occipital pole. The parieto-occipital sulcusjoins the calcarine sulcus at an acute angle a little in front of its middle,dividing it into anterior and posterior portions and forming an Y-shaped figure.

Cuneus

If the lips of the parieto-occipital sulcus and calcarine sulcus are widelyseparated, it will be seen that although on the surface they appear tobe continuous, they are separated from each other by a small buriedvertical cuneate gyrus called cuneus.

Histology of the Visual Cortex

There are six layers of the visual cortex (Fig. 5.10) histologically. Fromexternal to internal they are:• Layer I—plexiform lamina• Layer II—external granular lamina• Layer III—pyramidal lamina• Layer IV—internal granular lamina: this in turn is divided into

Layer IV A, Layer IV B and layer IV C alpha and Layer IV C beta• Layer V—ganglionic lamina• Layer VI—multiform lamina.

Fig. 5.9: Visual cortex


Parastriate Cortex

The visual picture from both the eyes unites in the parastriate cortexcalled area 18. The lips of the lunate sulcus separate area 17 from area19. Area 18 is buried within the walls of the sulcus and is in betweenarea 17 and area 19.

Peristriate Cortex

This is area 19. Most of area 19 lies in the posterior parietal lobe butinferiorly it forms part of the temporal lobe. In area 19 the object seenis recognized.

LOCALIZATION IN THE VISUAL PATHWAY

Retina

The nerve fibers converge towards the disk on the temporal side inthe important papillomacular bundle. There is no overlap betweenthe upper and lower halves of the fibers of the peripheral parts of theretina. In the retina the line dividing nasal from temporal fibers, inthe sense of those that will cross the chiasma and those that will not,passes through the center of the fovea. Hence, the temporal macular

Fig. 5.10: Histological layers of the cortex

Visual Pathway 85

fibers remain on the same side while the nasal ones cross. The uppertemporal retinal fibers are separated from the lower by the macularfibers—an arrangement, which holds throughout the central visualpathway.

Optic Nerve

In the optic nerve head In the optic nerve head the arrangement of thenerve fibers is exactly as in the retina.

In the optic nerve just behind the eyeball Here the nerve fibers aredistributed like in the retina (Fig. 5.11). The upper temporal and lowertemporal fibers which are situated on the temporal half of the opticnerve and are separated from each other by a wedge-shaped areaoccupied by the papillomacular bundle. The upper and lower nasalfibers are situated on the nasal side.

In the optic nerve near the chiasma Here the macular fibers arecentrally placed (Fig. 5.11).

Fig. 5.11: Arrangement of visual fibers in the optic nerve and tract


Optic Chiasma

The Nasal Fibers

The nasal peripheral fibers constitute about three-quarter of all thefibers and cross over to enter the medial part of the opposite optictract in the following manner.

The lower nasal fibers in the optic nerve traverse (Fig. 5.12) the chiasmalow and anteriorly So they are first affected in the tumors of the pituitarybody producing upper temporal quadrantic field defects. These fibersform convex loops called Wilbrand’s knee in the terminal part of theopposite optic nerve therefore ipsilateral blindness due to lesions ofthe proximal most part of the optic nerve is associated withcontralateral field defects. They then cross to the opposite tract andoccupy its lower quadrant.

The upper nasal fibers of the optic nerve traverse the chiasma high andposteriorly Therefore, they are involved first by lesions coming fromabove the chiasma, e.g. craniopharyngioma. After crossing they occupythe upper nasal quadrant of the opposite optic tract. Some of thesefibers make a loop in the ipsilateral optic tract before crossing.

Fig. 5.12: Arrangement of visual fibers in the optic chiasmaUN – Upper nasal fibers; LN – Lower nasal fibers; UT – Upper temporal fibers; LT– Lower temporal fibers; M – Macular fibers

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The Temporal Fibers

The temporal fibers from the retina which occupy the temporal halfof the optic nerves, remain uncrossed and run backwards in the lateralpart of the optic chiasma to reach the dorsolateral part of the optictract.

The Macular Fibers

The macular fibers, which occupy the central part at the proximal endof the optic nerve, keep this position in the anterior part of the chiasma.Then the crossing (nasal) macular fibers get separated from theuncrossed fibers and pass as a bundle obliquely backwards andupwards to decussate in the posterior most part of the chiasma, whichis related to the supraoptic recess. Lesions here may produce centraltemporal hemianopic scotoma.

Optic Tract

In the chiasma, crossed and uncrossed fibers are intermingled andwhen they reach the optic tract they are rearranged to correspondwith their position in the LGB. The macular fibers (Fig. 5.11) occupyarea of the cross-section dorsolaterally. The fibers from the lowerretinal quadrants are lateral and those from the upper are medial.


The fibers from the upper part of the retina go to the medial part ofthe LGB and those from below to the lateral part (Fig. 5.13). Themacular area is somewhat cuneiform and is confined to the posteriortwo/third of the nucleus, broadening towards the caudal pole.

The neurons of the LGB go to the visual cortex (Fig. 5.1). Theaxons of the ganglion cells synapse with the dendrites of the neuronsof the LGB. There is a regular point to point localization of the retinain the LGB nucleus, which is also carried from the latter to the visualcortex. The LGB has 6 lamina (1-6). The crossed fibers end in thelaminae 1, 4 and 6 (Fig. 5.14) while the uncrossed fibers end in thelaminae 2, 3 and 5, in such a way that those from the correspondingparts of the two retinae end in neighboring part of the adjacent laminae.Therefore, the smallest lesion of the retina results in degeneration ofthree laminae of the LGB in which the retinal fibers end. Hence, theconducting unit in optic nerve fibers is a 3-laminae unit. Since theoptic radiations commence from all the six laminae (6-laminae unit),so a lesion in the visual cortex results in degeneration of all the 6laminae of the LGB.


Optic Radiation

In the optic radiations (Fig. 5.13), there occurs a temporal rotation ofthe fibers. So, the upper retinal fibers occupy the upper part of theoptic radiations and the lower retinal fibers occupy the lower part ofthe optic radiations. The macular fibers lie in the central part of theoptic radiations separating the upper retinal fibers from the lowerretinal fibers.

Visual Cortex

The visual cortex is also called the cortical retina, since a true copy ofthe retinal image is formed here. It is only in the visual cortex that theimpulses originating from the two retinae meet. There is a point topoint representation of the retina in the visual cortex. The right visualcortex is concerned with perception of objects situated to the left ofthe vertical median line in the visual fields and left visual cortex withthe objects situated to the right half. In other words, the right visualcortex receives impulses arising from the temporal half of the right

Fig. 5.13: Arrangement of visual fibers in thelateral geniculate body and optic radiations

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retina and nasal half of the left retina. The left visual cortex receivesimpulses arising from the temporal half of the left retina and nasalhalf of the right retina.

The visual fibers contained in the optic radiations are relayed inthe visual cortex in the following manner (Fig. 5.15). Fibers from themacular area relay in an extensive area placed posteriorly in the visualcortex. Fibers from the peripheral retina end anterior to the macularfibers. Those from the upper retina go above the calcarine sulcus.

BLOOD SUPPLY OF THE VISUAL PATHWAY

Introduction

The visual pathway receives its blood supply from the two arterialsystems, the carotid and the vertebral connected to each other at the

Fig. 5.14: Arrangment of the axons of ganglioncells in the lateral geniculate body


base of the brain by the circle of Willis. The branches of the carotidsystem which contribute to the blood supply of the visual pathwayare ophthalmic artery, small branches of the internal carotic artery, posteriorcommunicating artery, anterior cerebral artery and middle cerebral artery.The arteries of the vertebral systems are cortical, central and choroidalbranches from the posterior cerebral artery. Similar to the brain, the visualpathway is mainly supplied by the pial network of vessels except theorbital part of the optic nerve, which is also supplied by an axial systemderived from the central retinal artery.

Retina

Choriocapillaries supply the outer four layers of the retina—thepigment epithelium layer, the layers of rods and cones, external limitingmembrane, and the outer nuclear layer.

Central retinal artery supplies the inner six layers—outer plexiformlayer, inner nuclear layer, inner plexiform layer, ganglion cell layer,nerve fibre layer, and internal limiting membrane.

The outer plexiform layer gets dual blood supply from choriocapillaries and central retinal artery. The rational vessels are endarteries.

Optic Nerve

Read Chapter 6 on Anatomy of the Optic Nerve.

Fig. 5.15: Arrangement of visual fibers in the visual cortex

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Fig. 5.16: Blood supply of the visual pathway

Optic Chiasma

The vessels may enter the chiasma directly or through the pial plexus.The main blood supply of the chiasma (Fig. 5.16) is through the anteriorcerebral artery and the internal carotid artery.• The superior aspect of the chiasma is supplied by branches from

the anterior cerebral artery and the anterior communicating artery• The inferior aspect of the chiasma is supplied by branches form

the internal carotid artery and the posterior communicating artery.A branch from the ophthalmic artery supplies the anteroinferiormargin of the chiasma.The venous drainage of the chiasma is as follows:

• The superior aspect of the chiasma is drained by the superiorchiasmal vein which ends in the anterior cerebral vein

• The inferior aspect of the chiasma is drained by the preinfundibularvein which drains into the basal vein.

Optic Tract

The pial plexus supplying the optic tract receives contributions from:• Posterior communicating artery• Anterior choroidal artery• Branches from the middle cerebral artery.


Though there is no anastomosis, there is considerableoverlapping in the blood supply of the optic tract by the anteriorchoroidal artery and the branches of the middle cerebral artery.Therefore, occlusion of the anterior choroidal artery does not resultin hemianopia.

The venous drainage from the superior aspect of the optic tractis through the anterior cerebral vein and from the inferior aspectof the optic tract through the basal vein.


The blood supply of the LGB is as follows:• Posterior cerebral artery supplies the posteromedial aspect of the

LGB and thus nourishes the fibers coming from the superiorhomonymous quadrants of the retina

• Anterior choroidal artery almost solely nourishes the anterolateralaspect of the LGB and thus supplies the fibers coming from theinferior homonymous quadrants of the retina

• The region of the hilum, which contains the macular fibers, issupplied by a rich anastomosis from both the posterior cerebraland the anterior choroidal arteries.Venous drainage of the LGB is through the basal vein.

Optic Radiations

The blood supply of the optic radiations is as follows:• Anterior choroidal artery supplies the optic radiations anteriorly• Deep optic artery (lateral striate artery) which is a branch of the

middle cerebral artery supplies the middle part of the opticradiations

• Calcarine branches of the posterior cerebral artery and perforatingbranches from the middle cerebral artery supply the posterior partof the optic radiations as the fibers spread out to reach the visualcortex.Venous drainage from the optic radiations is mainly by the basal

vein and in some parts by the middle cerebral vein.

Visual Cortex

Blood supply of the visual cortex is by:• Posterior cerebral artery supplies the visual cortex mainly through

the calcarine artery

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• The terminal branches of the middle cerebral artery supply theanterior end of the calcarine sulcus and the lateral aspect of theoccipital pole. At the posterior pole, there exists a rich anastomosisbetween the posterior and middle cerebral artery.Venous drainage from the medial aspect of the occipital cortex isby the internal occipital vein, which ends into the great cerebralvein of Galen and straight sinus. The superolateral aspect of thecortex drains into the inferior cerebral vein, which ends in thecavernous sinus.

LESIONS OF THE VISUAL PATHWAYAND FIELD DEFECTS

Optic Nerve Type Field Defects

Retinal nerve fibers enter the optic disk in a specific manner (Fig.5.17). So, nerve fiber bundle defects are of three basic types:

Papillomacular Bundle

Macular fibers enter the temporal aspect of the disk. A defect in this bundleof nerve fibers results (Fig. 5.18) in one of the following:• Central scotoma—a defect covering central fixation• Centrocecal scotoma—a central scotoma connected to the blind

spot (the cecum)• Paracentral scotoma—a defect of some of the papillomacular fibers

lying next to but not involving central fixation.

Fig. 5.17: Arrangement of nerve fibers in the retinal


Fig. 5.18: Papillomacular bundle field defects

Fig. 5.19: Nerve fiber bundle defects

Arcuate Nerve Fiber Bundle

Fibers from the retina temporal to the disk enter the superior and inferior polesof the disk. A defect in these bundles (Fig. 5.19) may cause any of the following:• Seidel scotoma—a defect in the proximal portion of the nerve fiber

bundle causes a comma-shaped extension of the blind spot calleda Seidel’s scotoma

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• Bjerrum, arcuate or scimitar scotoma—this arcuate portion of thefield at 15 degrees from fixation is known as Bjerrum’s area

• Isolated scotoma within Bjerrum’s area—this is due to a defect ofthe intermediate portion of the arcuate nerve fiber bundle

• Nasal step of Ronne—a defect in the distal portion of the arcuatenerve fiber bundles produces a nasal step of Ronne. Since thesuperior and inferior arcuate bundles do not cross the horizontalraphe of the temporal retina, a nasal step defect respects thehorizontal (180 degrees) meridian.

Nasal Nerve Fiber Bundle Defects

Fibers that enter the nasal aspect of the disk course in a straight(nonarcuate) fashion. The defect in this bundle results in a wedge-shaped temporal scotoma arising from the blind spot and does notnecessarily respect the temporal horizontal meridian.

Remember, nerve fiber bundle defects arise from the blind spot and notfrom the fixation point (Fig. 5.20). They do not respect the vertical meridianbut respect the nasal horizontal meridian. If a person has a quadranticfield defect, then check if the field defect originates from the fixationpoint or from the blind spot. If it originates from the fixation point itis a retrochiasmal lesion and if it originates from the blind spot it is anoptic nerve lesion. Other findings to check for an optic nerve lesion isdecreased visual acuity, which generally will not occur in retrochiasmallesions.

Fig. 5.20: Quadrantic field defects – differentiation betweenretrochiasmal lesion and an optic nerve lesion


Optic Chiasma Lesions

The following defects can occur in optic chiasmal lesions (Figs 5.21and 5.22).

Bitemporal Hemianopia

The nasal retinal fibers including the nasal half of the macula of eacheye cross in the chiasma, to the contralateral optic tract. The temporalfibers remain uncrossed. Thus, a chiasmal lesion will cause a bitemporalhemianopia due to interruption of the decussating nasal fibers.

Central Bitemporal Hemianopia

Macular crossing fibers pass in the posterior part of the chiasma andare related to the supraoptic recess. Lesions here can produce a centralbitemporal hemianopia.

Junctional Scotoma

A central scotoma in one eye with a superotemporal quadrantic defectin the other eye indicates a lesion at the junction of the optic nerve

Fig. 5.21: Lesions in the optic chiasmaUN – Upper nasal fibers; LN – Lower nasal fibers; UT – Upper temporal fibers;LT – Lower temporal fibers; M – Macular fibers

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Fig. 5.22: Field defects in chiasmal lesions

(RE in this case) and the chiasma. The lower nasal fibers cross in thechiasma and course anteriorly approximately 4 mm in the contralateraloptic nerve. This is Wilbrand’s knee (Fig. 5.12). Then they turn backto join uncrossed lower temporal fibers in the optic tract. A lesioninvolving the Wilbrand’s knee creates the junctional scotoma. Animportant gem to remember this is the J Lawton Smith super gem. If apatient comes with poor vision in the right eye, the important eye forvisual field examination is the left eye. There may be an uppertemporal defect with respect for the vertical meridian, due toinvolvement of the Wilbrand’s knee. The lesion is now intracranial atthe junction of the right optic nerve and chiasma. The field defectsconstitute a junctional scotoma.

Upper Temporal Quadrantic Defects

The lower nasal fibers travel low and anteriorly (Fig. 5.12) in theoptic chiasma. Thus, pituitary tumors can affect them. Thus, theyproduce upper temporal quadrantic defects.


Lower Temporal Quadrantic Defects

The upper nasal fibers travel high and posteriorly. Thus, a lesion fromabove the chiasma like a craniopharyngioma can produce a lesionhere. These produce a lower temporal quadrantic defect.

Optic Tract Lesions

All retrochiasmal lesions result in a contralateral homonymoushemianopia. In the optic tracts and LGB, nerve fibers of correspondingpoints do not yet lie adjacent to one another. This leads to incongruousvisual field defects. When we use the term congruous it meanshomonymous hemianopic defects that are identical in all attributeslike location, size, shape, depth and slope of margins. Thus in optictract lesions, there is an incongruous homonymous hemianopia(Fig. 5.23).

Lateral Geniculate Body Lesions

A lesion in the lateral geniculate body is extremely rare. Two types of defectscan occur. They are:• Incongruous homonymous hemianopia• Relatively congruous homonymous horizontal sectoranopia

(Fig. 5.23) associated with sectorial optic atrophy. This is due tovascular infarction of the LGB.

Fig. 5.23: Field defects in optic tract and lateral geniculate body lesions

Visual Pathway 99

Fig. 5.24: Lesions in the optic radiations and visual cortex

Optic Radiations and Visual Cortex Lesions

Various lesions (Fig. 5.24) can occur in the optic radiations and visualcortex. Depending on the site of lesion, various field defects can occur.

Temporal Lobe Lesions

Inferior fibers course anteriorly from the LGB into the temporal lobe,forming Meyer’s loop, approximately 2.5 cm from the anterior tip ofthe temporal lobe. They are separated from the superior retinal fibers,which course directly back in the optic radiations of the parietal lobe.Anterior temporal lobe lesions (Fig. 5.25) tend to producemidperipheral and peripheral contralateral homonymous superiorquadrantanopia. This is called a pie in the sky field defect.


Parietal Lobe Lesions

The superior fibers cross directly through the parietal lobe to liesuperiorly in the optic radiations. The inferior fibers course throughthe temporal lobe (Meyer’s loop) and lie inferiorly in the opticradiations. Thus, there is a correction of the 90 degree rotation of thevisual fibers that occurred through the chiasma into the tracts. Parietallobe lesions (Fig. 5.26) tend to produce contralateral inferiorhomonymous quadrantanopia as they affect the superior fibers first.

Occipital Lobe Lesions

Central homonymous hemianopia In the visual cortex, the macularrepresentation is located on the tips of the occipital lobes. A lesionaffecting the tip of the occipital lobe tends to produce a centralhomonymous hemianopia (Fig. 5.27).

Macular sparing The macular area of the visual cortex is a watershedarea with respect to the blood supply (Fig. 5.16).

Terminal branches of the posterior cerebral and middle cerebralarteries supply the macular visual cortex. Only the posterior cerebralartery supplies the visual cortex subserving midperipheral andperipheral fields. A more proximal (not terminal) vessel supplies thearea. Therefore, when there is obstruction of flow through theposterior cerebral artery, ipsilateral macular visual cortex may bespared, because of blood supply provided by the terminal branchesof the middle cerebral artery. This may be an explanation of macularsparing (Fig. 5.27). However, when there is a generalizedhypoperfusion state (e.g. intraoperative hypotension), the first area

Fig. 5.25: Field defect due to temporal lobe lesions. Anterior temporal lobe lesionsof Meyer’s loop produce incongruous midperipheral and peripheral contralateralhomonymous superior quadrantanopia. This is a pie in the sky field defect. Thiscase is an example of a right temporal lobe lesion

Visual Pathway 101

Fig. 5.26: Field defect due to parietal lobe lesions. Parietal lobe lesions affect thesuperior fibers first and so produce a contralateral inferior homonymousquadrantanopia. This is a case of a right parietal lobe lesion

Fig. 5.27: Field defects due to occipital lobe lesions


of the visual cortex to be affected is that supplied by terminal branches,the macular visual cortex, resulting in a central homonymoushemianopia. To say the patient has macular sparing at least 5 degreesof the macular field must be spared in both eyes, on the side of thehemianopia.

Temporal crescents When we fixate with both eyes and achieve fusionof the visual information gained by both eyes, there is superimpositionof the corresponding portions of the visual fields—the central 60degrees radius of field in each eye. There remains in each eye, atemporal crescent of field for which there are no corresponding visualpoints in the other eye. This temporal crescent of field, perceived bya nasal crescent of retina, is represented in the contralateral visualcortex, in the most anterior portion of the mesial surface of the occipitallobe along the calcarine fissure. If a patient has a homonymous hemi-anopia with sparing of the temporal crescent (Fig. 5.27), the patienthas an occipital lobe lesion, since this is the only site where the temporalcrescent of fibers are separated from the other nasal fibers of thecontralateral eye.

Riddoch phenomenon This is a rare visual field sign. Riddoch believedthat patients with severe field loss from occipital lobe involvementperceive from and movement separately. He postulated that perceptionof movement recovers before perception of form and that thisphenomenon was of some prognostic value for recovery of field. Thisphenomenon is illustrated in the patient with extensive densehomonymous hemianopia as a result of an occipital lobe lesion. Thepatient cannot see a large stationary object in the blind field but cansee a smaller object, if it is moving.

Altitudinal defect Injury to both occipital poles may result inaltitudinal field defects. When the upper portions of the visual cortexor posterior radiation are damaged, the resultant field defects arealtitudinal with loss of the entire lower field of vision of both eyes. Ifthe lower portion of the lobes are damaged, death usually occursafter intracranial bleeding as a result of laceration of dural sinuses.

REFERENCES



6Anatomy of

the Optic NerveAthiya Agarwal

INTRODUCTION

Optic nerve, or the second cranial nerve is 5 cm in length and has fourportions.1,2 They are: (i) intracranial, (ii) intracanalicular, (iii)intraorbital, and (iv) intraocular portion.

Although we speak of the optic nerve, it is very important to realizethat it is really no nerve at all, but essentially a fiber tract joining twoportions of the brain. The evidence for this is uncontrollable. Theyare:• It is an outgrowth of the brain• Its fibers possess no neurolemmal cells• It is surrounded by the meninges, unlike any peripheral nerve• Both the primary and secondary neurons are in the retina.

COURSE

Intracranial Portion

The optic nerve ensheathed in pia runs as a flattened band from theanterolateral angle of the somewhat quadrilateral optic chiasma. Itruns forwards and laterally and slightly downwards to the opticforamen.

Intracanalicular Portion

At its entry into the optic canal, it receives a covering of arachnoidmater and since the dura mater is prolonged through the canal as aperiosteum, the nerve is in fact from here onwards surrounded by allthree meninges and also of course, the cerebrospinal fluid. It traversesthe optic canal and enters the orbit.


Intraorbital Portion

As a rounded cord, it now runs forwards and slightly laterally anddownwards in a somewhat sinuous manner to allow for ocularmovements and is continued into the back of the eyeball.

Intraocular Portion

It then enters the eyeball just above and 3 mm medial to the posteriorpole.

RELATIONS

Intracranial Portion

The nerve lies at first above the diaphragma sellae, which covers thepituitary body. Between the two nerves in front of the chiasma is atriangular space in which is a variable portion of the pituitary, coveredby the diaphragma sellae. Above the nerve is the anterior perforatedsubstance, the medial root of the olfactory tract and the anteriorcerebral artery, which crosses superiorly to reach its medial side. Theinternal carotid artery is at first below and then lateral.

Intracanalicular Portion

The pia forms a sheath closely adherent to the nerve (Fig. 6.1). Thedura constitutes the periosteal lining to the canal and at its orbitalend splits to become continuous on the one hand with the periorbitaand on the other hand with the dura of the optic nerve.

The ophthalmic artery crosses below the nerve in the dural sheathto its lateral side. It leaves the dura at or near the anterior end of thecanal. Thus, the internal carotid artery is to some extent tied to thedural sheath by its ophthalmic branch and it is also indirectly attachedto the optic nerve by the adherence of the sheaths and by branches tothe nerve from the ophthalmic artery.

Medial to the optic nerve is the sphenoidal air sinus or a posteriorethmoidal sinus, from which it may be separated by a thin plate ofbone only. This provides the explanation of retrobulbar neuritis following asinus infection.

Intraorbital Portion

At the optic foramen, the nerve is surrounded by the origin of theocular muscles. The superior and medial rectus are closely adherentto the dural sheath. It is this connection which gives rise to the pain in

Anatomy of the Optic Nerve 105

extreme movements of the globe, so characteristic of retrobulbar neuritis.Between the optic nerve and the lateral rectus are the divisions of theIII cranial nerve, nasociliary nerve, sympathetic nerves and the VIcranial nerve.

The nasociliary nerve, ophthalmic artery and superior ophthalmicvein cross the nerve superiorly between the nerve and the superiorrectus from its lateral to medial side. The ciliary ganglion is lateral tothe nerve between the nerve and the lateral rectus.

The central retinal artery near the optic foramen, runs forwards inor outside the dural sheath of the nerve. Then it crosses thesubarachnoid space to enter the nerve on its under and medial aspectabout 12 mm behind the eye.

Intraocular Portion

The intraocular portion passes through the sclera and choroid andfinally appears in the eye as the optic disk (Fig. 6.2). The intraocularportion of the optic nerve head has an average diameter of 1.5 mm,

Fig. 6.1: Sheaths of the optic nerve


which expands to approximately 3 mm just behind the sclera, wherethe neurons acquire a myelin sheath. The optic nerve head may bearbitrarily divided into the following four portions from anterior toposterior. They are:• Surface nerve fiber layer• Prelaminar region• Lamina cribrosa• Retrolaminar region.

Surface Nerve Fiber Layer

Surface nerve fiber layer is essentially composed of axonal bundles,i.e. nerve fibers of the retina, which converge on the optic disk andastrocytes. The optic disk is covered by a thin layer of astrocytes, theinternal limiting membrane of Elschnig, which separates it from thevitreous and is continuous with the internal limiting membrane of theretina (Fig. 6.2). When the central portion of this membrane isthickened, it is referred to as the central meniscus of Kuhnt. All thelayers of the retina, apart from the nerve fiber layer, near the optic

Fig. 6.2: Optic nerve head

Anatomy of the Optic Nerve 107

nerve are separated from it by a partial rim of glial tissue called theintermediary tissue of Kuhnt.

Prelaminar Region

The predominant structures at this level are neurons and a significantlyincreased quantity of astroglial tissue. The border tissue of Jacoby(a cuff of astrocytes) separates the nerve from the choroid.

Lamina Cribrosa

It is a fibrillar sieve-like structure made up of fenestrated sheets ofscleral connective tissue lined by glial tissue. It bridges the posteriorscleral foramina or the scleral canal. The bundles of optic nerve fibersleave the eye through these fenestrations. A rim of collagenousconnective tissue with some admixture of glial cells, which intervenesbetween the choroid and sclera and optic nerve fibers, is called theborder tissue of Elschnig. The lamina cribrosa gets its rich blood supplyfrom the circle of Zinn.

Retrolaminar Region

This area is characterized by a decrease in astrocytes and theacquisition of myelin that is supplied by oligodendrocytes. Theaddition of myelin sheath nearly doubles the diameter of the opticnerve from 1.5 to 3 mm. The axonal bundles are surrounded byconnective tissue septa.

BLOOD SUPPLY OF THE OPTIC NERVE

Intracranial Part

This part of the optic nerve is supplied by the periaxial system of vessels. Thepial plexus is contributed by four sources:• Internal carotid artery• Anterior cerebral artery• Ophthalmic artery• Anterior communicating artery.

Intracanalicular Part

The nerve within the optic canal is supplied by the periaxial system ofvessels. The pial plexus in this part is fed mainly by branches from theophthalmic artery.


Intraorbital Part

The intraorbital part is supplied by two systems of vessels.• The periaxial system—supplying the optic nerve is derived from

the 6 branches of the internal carotid artery, namely ophthalmicartery, long posterior ciliary artery, short posterior ciliary artery,lacrimal artery, central retinal artery before it enters the optic nerveand circle of Zinn.

• The axial system—supplying the axial part of the optic nerve isderived from the intraneural branches of the central retinal artery,central collateral arteries which come off from the central retinalartery before it pierces the nerve and central artery of the opticnerve.The capillary network for the optic nerve is derived from both the

systems. Anastomosis between the two systems has also beendemonstrated.

Intraocular Part

This is the optic nerve head, which has 4 portions:• The surface nerve fiber layer—is mainly supplied by the capillaries

derived from the retinal arterioles. These anastomose with vesselsof the prelaminar region. Occasionally a ciliary-derived vessel fromthe prelaminar region may enlarge to form the cilioretinal artery

• The prelaminar region—is supplied by vessels of the ciliary region• The lamina cribrosa region—is also supplied by the ciliary vessels

which are derived from the short posterior ciliary arteries andarterial circle of Zinn-Haller

• The retrolaminar region—is supplied by both the ciliary and retinalcirculation with the former coming from the recurrent pial vessels.The central retinal artery provides centripetal branches from thepial plexus and also centrifugal branches.

REFERENCES



7 Oculomotor Nerve

Athiya Agarwal

INTRODUCTION

The oculomotor (third cranial) nerve is entirely motor in function.1,2

It supplies all the extraocular muscles except the lateral rectus andsuperior oblique. It also supplies the sphincter pupillae and the ciliarymuscle.

NUCLEUS

The nucleus of the oculomotor nerve lies in the midbrain at the levelof the superior colliculus (Fig. 7.1). The oculomotor nucleus complexhas two motor nuclei.

The main motor nucleus. This is composed of the subnuclei supplyingindividual extraocular muscles as follows:• Dorsolateral nucleus—ipsilateral inferior rectus• Intermedial nucleus—ipsilateral inferior oblique• Ventromedial nucleus—ipsilateral medial rectus• Paramedial (scattered) nucleus—contralateral superior rectus• Caudal central nucleus—bilateral levator palpebrae superioris.

The accessory motor nucleus (Edinger-Westphal nuclei). It is situatedposterior to the main oculomotor nucleus mass. It consists of a medianand two lateral components. Perhaps the cranial half of the nucleus isconcerned with light reflexes and the caudal half with accommodation.The median part is fork shaped (nucleus of Perlia) and its role inconvergence is questionable.

Important points to remember is that both the LPS are supplied by onecentral caudal nucleus and each SR is supplied by the opposite III nervenucleus.


EXIT FROM THE BRAIN

The nerve starts from the third nerve nucleus (Fig. 7.2) and passesthrough the red nucleus. It then passes through the corticospinal(pyramidal) tract and emerges from the midbrain and passes into theinterpeduncular space (Fig. 7.3). The nerve passes between theposterior cerebral artery and the superior cerebellar artery to reachthe cavernous sinus.

We should at this stage also understand the relations of the othercranial nerves when they exit from the brain (Fig. 7.3). The IV cranialnerve comes out dorsally and passes between the posterior cerebraland superior cerebellar arteries. The V nerve comes out from thepons. Between the two V nerves is the pons. Lateral to the V nerve isthe middle cerebellar peduncle. The VI, VII and VIII nerve come outbetween the pons and medulla oblongata. The VI nerve comes out atthe level of the pyramid (part of medulla oblongata), the VII nervecomes out at the level of the olive (part of medulla oblongata) and theVIII nerve comes out at the level of the inferior cerebellar peduncle(part of medulla oblongata). The IX, X and XI nerves come out betweenthe olive and the inferior cerebellar peduncle and the XII nerve comesout between the olive and the pyramid.

Fig. 7.1: Third nerve nucleus

Oculomotor Nerve 111

Fig. 7.2: Pathway of oculomotor nerve

Fig. 7.3: Location of exit of cranial nerves in the brain


CAVERNOUS SINUS

The oculomotor nerve is lateral to the posterior clinoid process andabove the attached margin of the tentorium cerebelli. It now lies lateralto the pituitary fossa above the cavernous sinus, then piercing thedura it passes through the roof and comes to lie in the lateral wall ofthe cavernous sinus (Fig. 7.4).

COURSE IN SUPERIOR ORBITAL FISSURE

The III cranial nerve now enters the superior orbital fissure (SOF) butjust before it does so it divides into a small superior and a largerinferior division. At about this point the IV nerve crosses the III nerveand lies above and then lateral to it.

Definition

Superior orbital fissure or sphenoidal fissure is an irregularly linearfissure situated in the most posterior part of the orbital cavity betweenthe posterior part of the lateral wall, roof and medial wall of theorbit.

Size2 cm long.

Fig. 7.4: Cavernous sinus


Shape

It is comma shaped or retort shaped (Fig. 7.5).

Limbs

It comprises two limbs—a narrow lateral part and a wider medialpart.

Borders

Superiorly, the lesser wing of the sphenoid forms the SOF, inferiorlyand laterally it is formed by the orbital process of the greater wing ofthe sphenoid, medially by the body of the sphenoid and the orbitalprocess of the perpendicular plate of the palatine bone.

Relations

The fissure is obliquely placed and its lower end is continuousanteriorly with the inferior orbital fissure and posteriorly with thepterygomaxillary fissure. Its medial end is separated from the opticforamen by the posterior root of the lesser wing of the sphenoid.

Common Tendinous Ring

This stretches across or lies across the fissure. It divides the fissureinto an upper lateral, middle and lower medial part.

Fig. 7.5: Superior orbital fissure


Contents

Passing above the annulus from medial to lateral is the:• Trochlear nerve• Frontal nerve• Lacrimal nerve• Recurrent meningeal branch of the lacrimal artery• Orbital branch of the middle meningeal artery• The superior ophthalmic vein also passes in this part.

Passing within the annulus or between the two heads of the lateral rectusis the following structures from above downwards;• Superior division of the III cranial nerve• Nasociliary nerve• Sympathetic root of the ciliary ganglion• Inferior division of the III cranial nerve• VI nerve.

As a rule nothing passes below the annulus, but rarely the inferiorophthalmic vein passes through it.

COURSE IN THE ORBIT

The superior division inclines medially above the optic nerve and justbehind the nasociliary nerve to supply the SR on its undersurface atthe junction of the middle and posterior thirds and the LPS. Theinferior division immediately divides into three. The branch to theMR passes under the optic nerve to enter the muscle. The branch tothe IR pierces the muscle on its upper aspect near the junction of themiddle and posterior thirds. The long branch to the IO runs along thefloor of the orbit on the lateral border of the IR or between this muscleand the LR. It crosses above the posterior border of the IO about itsmiddle and breaks up into 2 or 3 branches, which enter the uppersurface of the muscle. It is this nerve that gives the short stout branchto the ciliary ganglion for relay to the sphincter pupillae and the ciliarymuscle.

CILIARY GANGLION

Introduction

Ciliary ganglion is a peripheral parasympathetic ganglion placed inthe course of the oculomotor nerve. It lies near the apex of the orbitbetween the optic nerve and the tendon of the lateral rectus muscle.


Size

It measures about 2 mm anteroposteriorly and about 1 mm indiameter.

Color

Reddish gray.

Shape

Polygonal.

Roots

It receives posteriorly (Fig. 7.6) three so, called roots or rami.

Long or Sensory Root

Long or sensory root comes from the nasociliary nerve and is givenoff just after that nerve has entered the orbit. It is a slender nerveabout 5 to 10 mm long and passes along the lateral side of the opticnerve to reach the upper and posterior part of the ganglion. It containssensory fibers from the cornea, iris and ciliary body and possiblysympathetic fibers to the dilator pupillae.

Fig. 7.6: Ciliary ganglion


Short or Motor Root

Short or motor root comes from the nerve to the inferior oblique afew mm beyond the point where the nerve arises from the inferiordivision of the III nerve. It is much thicker than the sensory root andis about 1 to 2 mm long. It passes upwards and forwards to enter theposteroinferior angle of the ganglion. It carries parasympathetic fibersto the sphincter pupillae and the ciliary muscle. These synapse in theganglion.

Sympathetic Root

Sympathetic root comes from the plexus around the internal carotidartery. It passes through the superior orbital fissure within the annulustendinosus inferomedial to the nasociliary nerve. It lies below andclose to the long root with which it may be blended and enters theposterior border of the ganglion between the other roots. It carriesconstrictor fibers to the blood vessels of the eye and dilator fibers tothe pupil.

Branches

Short Ciliary Nerve

The somata of the preganglionic parasympathetic nerve fibers reachingthe ciliary ganglion are in the Edinger-Westphal nucleus. They are ofcourse myelinated. They end in the ganglion by forming synapseswith the somata and dendrites of the postganglionic neurons. Theseaxons form the short ciliary nerves. They are unique in the fact thatnormally postganglionic nerve fibers are not myelinated but they arethe exception to this rule and are myelinated. The short ciliary nervescontain small groups of displaced ganglion cells. The short ciliarynerves are 6 to 10 in number. They are delicate filaments, which comeoff in two groups from the anterosuperior and anteroinferior anglesof the ganglion respectively. They run sinuously with the short ciliaryarteries above and below the optic nerves, the lower group being thelarger. As they pass forwards, they connect with each other and withthe long ciliaries. Having given branches to the optic nerve and theophthalmic artery they pierce the sclera around the optic nerve. Theyrun anteriorly between the sclera and the choroid, grooving the sclera,to the ciliary muscle on the surface of which they form a plexus, whichsupplies the iris, ciliary body and the cornea (Fig. 7.7).


BLOOD SUPPLY

All nerves are supplied with blood vessels, which are essential fortheir normal functioning. The arteries supplying a nerve are derivedfrom adjacent vessels, which most often are of a small size. On reachingthe nerve the nutrient artery breaks up into ascending and descendingbranches which anastomose in the epineurium with similar branchesfrom other nutrient arteries. From such epineural vessels, branchespenetrate the perineurium where further anastomoses occurs andfinally small vessels penetrate into the fasciculi and from there a richlongitudinally disposed capillary network runs up and down the nervein unbroken continuity. This intrafascicular network is reinforced alongits length by contributions from the various nutrient vessels, whichreach the epineurium, but no part of the intrafascicular plexus may beregarded as being dominated by any one nutrient artery. In the sameway the III, IV and VI cranial nerves get their blood supply.

REFERENCES



Fig. 7.7: Supply of short ciliary nerves

8Lesions of the

Oculomotor NerveAthiya Agarwal

ETIOLOGY

The common causes of oculomotor nerve palsy are: neoplasms, trauma,aneurysms, ischemic lesions and others like ophthalmoplegicmigraine.1,2

GENETICS

Oculomotor nerve palsy could be congenital due to a hereditary cause.The mode of transmission could be either autosomal dominant orrecessive.

CLINICAL FEATURES

Total third nerve paresis may be central, sparing the pupil or peripheralwith pupillary involvement. If the pupil is spared, the most likelycause is a vascular lesion. If the pupil is involved, it is most likely dueto an aneurysm. The patient has a large exotropia with hypotropia. Afixed dilated pupil is seen. On attempted adduction, the eye intortsas the superior oblique would be normal. Excluding birth trauma, thecongenital form of external ophthalmoplegia has certain features—itis generally bilateral and the extraocular muscles can vary in theirdegree of involvement. One can also get partial paresis as the III nervedivides into a superior and an inferior division. If the superior divisionof the III nerve is involved, generally other cranial nerves are alsoinvolved. One can get an isolated involvement of the inferior divisionof the III cranial nerve.

NUCLEAR THIRD NERVE PARESIS

This is extremely rare and occurs if the lesion involves the III nerve nucleus(Fig. 8.1). The important points about this lesion are:

Lesions of the Oculomotor Nerve 119

• Each superior rectus is innervated by the contralateral third nervenucleus. So, if there were nuclear third nerve palsy on one sidethen there would be a paresis of the contralateral superior rectus.

• Both levator palpebrae superioris are innervated by one subnuclearstructure, the central caudal nucleus. Therefore, nuclear third nervepalsy leads to bilateral ptosis.

THIRD NERVE FASCICLE SYNDROMES

In these cases the III nerve has already left the nucleus, so the lesionsaffect only one side. There are various syndromes, which can occurdepending on the site of lesion (Fig. 8.1). They are due generally toan ischemic, infiltrative (tumor) or rarely inflammatory lesion.

Nothnagel’s Syndrome

In this case the lesion is in the area of the superior cerebellar peduncle.As the lesion involves the superior cerebellar peduncle the patienthas an ipsilateral third nerve paresis with cerebellar ataxia.

Benedict’s Syndrome

In this syndrome the lesion is in the area of the red nucleus. Thisleads to contralateral hemitremor with ipsilateral third nerve paresis.

Fig. 8.1: Syndromes of the oculomotor nerve


Claude’s Syndrome

This syndrome has features of both Nothnagel’s and Benedict’ssyndrome.

Weber’s Syndrome

In this the lesion is in the area of corticospinal (pyramidal) tract. Thisleads to an ipsilateral third nerve paresis with contralateral hemiparesis.

UNCAL HERNIATION SYNDROME

As the third cranial nerve goes towards the cavernous sinus, it restson the edge of the tentorium cerebelli. The portion of the brainoverlying the third nerve, at the tentorial edge, is the uncal portionof the undersurface of the temporal lobe. A supratentorial space-occupying mass located anywhere in or above this cerebralhemisphere, may cause a downward displacement and herniation ofthe uncus across the tentorial edge, thereby compressing the thirdnerve. This leads to a dilated and fixed pupil. (Fig. 8.2). This is calledthe Hutchinson pupil and is the first indication that altered consciousnessis due to a space-occupying intracranial lesion.

POSTERIOR COMMUNICATING ARTERY ANEURYSM

As the third cranial nerve moves towards the cavernous sinus, ittravels alongside the posterior communicating artery (Fig. 8.3). If thereis an aneurysm of the posterior communicating artery it can lead tocompression of the third nerve. This leads to an isolated third nerveparesis with the pupil getting involved.

Fig. 8.2: Hutchinson pupil

Lesions of the Oculomotor Nerve 121

CAVERNOUS SINUS SYNDROME

In the cavernous sinus syndrome, there would be third nerve paresiswith involvement of other nerves like IV, V and VI cranial nerves.The patients have painful ophthalmoplegia. This could be due totrauma, neoplasms, aneurysms or inflammations. This syndrome canlead to aberrant regeneration of the III cranial nerve.

ORBITAL SYNDROME

There can be proptosis as an early sign. The V cranial nerve can alsobe involved but this would involve only the ophthalmic division.

PUPIL-SPARING ISOLATED THIRD NERVE PARESIS

The pupillomotor fibers travel in the III nerve in the outer layers andare therefore closer to the nutrient blood supply enveloping the nerve.This is the reason why the pupillomotor fibers are spared generallyin ischemic third nerve paresis but are affected in compressive lesionslike tumors. Ocular myasthenia can mimic a pupil-sparing third nervepalsy, so one can perform the Tensilon test to differentiate the two.

ABERRANT REGENERATION OF OCULOMOTOR NERVE

Aberrant regeneration of the cranial nerve follows damage of thenerve by trauma or tumor.

Lid gaze dyskinesis• Elevation of the lid on adduction (inverse Duane’s sign)• Elevation of the lid on depression (pseudo Von Graffe’s sign)

Fig. 8.3: Posterior communicating artery aneurysm


Pupil gaze dyskinesis• Constriction on adduction (pseudo Argyll Robertson pupil)• Constriction on depression.

If aberrant regeneration occur spontaneously (primary regene-ration) without a preceding third nerve palsy usually is caused by acavernous sinus tumor or aneurysm.

As a rule aberrant regeneration never occurs in Ischemic III nervepalsy.

MANAGEMENT

Occlusion

One can occlude the paretic eye for sometime, till the healing occursand the III nerve paresis is cured.

Medical Treatment

One can give the patient multivitamin injections and tablets and treatthe cause like diabetes or hypertension.

Surgical Treatment

The surgical management of a complete III nerve paralysis is a difficultjob. At the very best, the surgeon will succeed only in moving theparetic eye into the primary position without restoring adduction,elevation or depression to a significant degree. A very good methodto treat this condition is to do a tenotomy of the lateral rectus and thesuperior oblique combined with a transposition of the vertical rectimuscles to the insertion of the medial rectus muscle. Even though thetreated eye will continue to be immobile, it will at least be centeredand this operation should be considered especially in patients whofixate with the paralyzed eye. For the ptosis one should perform afrontalis muscle sling operation. This can be done as a second step.

If the patient has a partial palsy with slight medial rectus movementone can perform a maximal recession of the lateral rectus muscle (atleast 12 mm) and resection of the medial rectus (at least 7 mm) withupward transposition of the tendons in case of an associatedhypotropia. This may restore a small but useful field of vision eventhough double vision will persist in up and downward gaze.

REFERENCES



9Trochlear Nerveand its Lesions

Athiya Agarwal

INTRODUCTION

The trochlear nerve is the fourth cranial nerve is the thinnest and alsohas the longest intracranial course of about 75 mm.1,2 This is the onlycranial nerve that comes out from the dorsal aspect of the brainstem.It is also the only cranial nerve that crosses completely to the oppositeside. In other words, the trochlear nerve arises from the contralateralnucleus (Fig. 9.1).

NUCLEUS

The trochlear nerve nucleus is situated in the midbrain at the level ofthe inferior colliculus. It is caudal to and continuous with the thirdnerve nucleus complex.

COURSE

Exit from the Nucleus

From each nucleus, the nerve fibers run laterally and emerge fromthe dorsal aspect of the midbrain at the level of the inferior colliculus.They pass medially and decussate completely. Thus, the IVth cranialnerve crosses to the opposite side and thus each superior oblique issupplied from the contralateral trochlear nucleus.

Exit from the Brain

Once the trochlear nerve exits from the brain from the dorsal side itturns towards the ventral side and passes between the posteriorcerebral artery and superior cerebellar artery. It then pierces the duraon the posterior corner of the roof of the cavernous sinus to enterinto it.


Cavernous Sinus

In the cavernous sinus, the nerve runs forwards in the lateral walllying below the oculomotor nerve and above the first division of thefifth cranial nerve. In the anterior part of the cavernous sinus it rises,crosses over the third nerve and leaves the sinus to pass through thelateral part of the superior orbital fissure.

Superior Orbital Fissure

The trochlear nerve enters the orbit through the lateral portion of thesuperior orbital fissure. The nerve passes medially above the originof the levator palpebrae superioris and ends by supplying the superioroblique muscle through its orbital surface.

Orbital Course

In the orbit, the trochlear nerve leaves the frontal nerve which is atfirst close to it at an acute angle and passes medially and forwards

Fig. 9.1: Trochlear nerve – anatomy

Trochlear Nerve and its Lesions 125

beneath the periosteum and above the levator palpebrae superiorisand superior rectus. It divides up in a fan-shaped manner into 3 or 4branches, which supply the superior oblique on its upper surface nearthe lateral border. The most anterior branch enters the muscle at thejunction of the posterior and middle thirds and the most posteriorsome 8 mm beyond its origin.

LESIONS OF THE TROCHLEAR NERVE

Depending on the level of the lesion, various syndromes can occurwith damage to the trochlear nerve. They are as follows:

Nuclear Fascicular Syndrome

It is difficult to distinguish between nuclear and fascicular lesionsdue to the short course of the fascicles within the midbrain (Fig. 9.2).It could be due to hemorrhage trauma or demyelination. It is seenwith contralateral Horner’s syndrome, since the sympathetic pathwaysdescend through the dorsolateral tegmentum of the midbrain adjacentto the trochlear fascicles.

Fig. 9.2: Lesions of trochlear nerve


Subarachnoid Space Syndrome

As the fourth nerve emerges from the dorsal surface of the brainstem,it can get injured easily. When bilateral fourth nerve palsies occur,the site of injury is likely in the anterior medullary velum. Contracoupforces transmitted to the brainstem by the free tentorial edge mayinjure the nerves at this site. Other causes could be tumors likepinealoma or tentorial meningiomas.

Cavernous Sinus Syndrome

If the lesion is in the cavernous sinus, other cranial nerves in closeassociation with the fourth cranial nerve also get involved.

Orbital Syndrome

In this other cranial nerves close to the fourth cranial nerve are alsoinvolved. Other orbital signs like proptosis, chemosis and conjunctivalinjection are also seen. This could be due to trauma, inflammation ortumors.

Isolated Fourth Nerve Palsy

Isolated fourth nerve palsy could be due to a congenital cause or itcould be acquired. The features of a fourth nerve palsy are:

Hyperdeviation

The involved eye is higher as a result of the weakness of the superioroblique muscle. One should perform the Bielschowsky’s head tiltingtest, as when the head is tilted towards the ipsilateral shoulder thehyperdeviation becomes more obvious.

Ocular Movements

Depression is limited in adduction. Intorsion is also limited.

Diplopia

Homonymous vertical diplopia occurs on looking downwards. Usuallythe vision is single as long as the eyes look above the horizontal plane.The patient especially notices diplopia when coming down the stairs.

Abnormal Head Posture

To avoid diplopia, the head takes an abnormal head posture towardsthe action of the superior oblique muscle, i.e. the face is slightly turned


to the opposite side, chin is depressed and the head is tilted towardsthe opposite shoulder.

CHECKING FOURTH NERVE FUNCTION INTHE SETTING OF A THIRD NERVE PARESIS

The problem to check the fourth cranial nerve function, if a patientalso has a third cranial nerve paresis is that the involved eye cannotbe adducted well due to the third cranial nerve involvement. As theeye cannot be adducted, one cannot test the vertical action (depression)of the superior oblique muscle.

To solve this problem, first of all we should note a limbal orconjunctival landmark like a blood vessel or pterygium. Then, ask thepatient to look down. The patient will not be able to look down asthe eye is abducted and not adducted (due to the third nerveinvolvement). But the eye will intort as the superior oblique works.We should then check from the conjunctival landmark if the eye isintorting. If the conjunctival landmark is moving, the eye is intortingand that means the fourth nerve is intact.

BIELSCHOWSKY’S HEAD TILTING TEST

The Bielschowsky’s head tilting test can diagnose which muscle isparalyzed. Let us first of all look at a case of R/L hypertropia inwhich the right eye is at a higher position than the left eye (Fig. 9.3).

R/L Hypertropia

If the patient has a R/L hypertropia, then it could mean that the righteye is hypertropic in which case the depressors are paralyzed like theRIR or the RSO. It could also mean that the right eye is in the normalposition but the left eye is hypotropic. This could be due to the elevatorsof the left eye being paralyzed like the LIO and the LSR. This is thefirst step or I step of the test. Out of the extraocular muscles we havenarrowed down the diagnosis to four muscles.

Now, we perform the II step of the test. In this we ask the patientto perform dextroversion or levoversion. This means we ask thepatient to look to the right and to the left. If we ask the patient tolook to the right, the right eye could be higher than the left eye. If theright eye is higher on dextroversion, then it could mean that the RIRis involved or it could mean that the left eye is hypotropic. This wouldbe due to a LIO paralysis. In levoversion if the right eye is higher itcould be due to a RSO paralysis. Alternately, it could mean that the


left eye is hypotropic and this would be due to LSR paralysis. Thus,we have narrowed down the muscles from 4 to 2.

Finally, we perform the III step in which we tilt the patient’s headto the right and then to the left. If we tilt the head to the right, theright eye will intort and the left eye will extort. This is because nervousimpulses will be sent from the semicircular canals to keep the eyes ina straight position. Now, remember the superiors are intorters. So, if theright eye intorts, it means the superiors in that eye (RSR and RSO)work and if the left eye extorts it means the inferiors of that eye (LIOand LIR) work. When this happens in the right eye the RIR will not beused at all as it is an extorter and in the right eye extortion is nottaking place. But, in the left eye, extortion will take place and the LIOand LIR will work. Now, the LIO is paralyzed and so cannot work.This will make the LIR only work in that eye and as a balance will notbe maintained between these two muscles the left eye will move downas the LIR is also a depressor. Thus, one can diagnose the case of LIO.

If we ask the patient to tilt the head to the left, the left eye willintort and the right eye will extort. In the right eye the extorters will

Fig. 9.3: Bielschowsky’s head tilting test for R/L hypertropia


be the RIR and RIO. Now the RIR is paralyzed and so the RIO willonly work and the right eye will move upwards.

Similarly, we can differentiate between the RSO and the LSR inthe III step. If we tilt the head to the right, the right eye will intortand the muscles that will work are the RSO and RSR. As the RSO isparalyzed the RSR will only work and the right eye will moveupwards.

If we tilt the head to the left, the left eye will intort and the musclesthat will work are the LSR and LSO. If the LSR is paralyzed the LSOwill work and the left eye will move down.

L/R Hypertropia

If we now work on the same principle and get the muscle involved ina L/R hypertropia (Fig. 9.4).

If the patient has a L/R hypertropia, then it could mean that theleft eye is hypertropic in which case the depressors are paralyzed likethe LIR or the LSO. It could also mean that the left eye is in thenormal position but the right eye is hypotropic. This could be due tothe elevators of the right eye being paralyzed like the RIO and the

Fig. 9.4: Bielschowsky’s head tilting test for L/R hypertropia


RSR. This is the first step or I Step of the test. Out of the extraocularmuscles we have narrowed down the diagnosis to 4 muscles.

Now, we perform the II Step of the test. In this we ask the patientto perform dextroversion or levoversion. This means we ask thepatient to look to the right and to the left. If we ask the patient tolook to the right, the left eye could be higher than the right eye. If theleft eye is higher on dextroversion, then it could mean that the LSO isinvolved or it could mean that the right eye is hypotropic. This wouldbe due to a RSR paralysis. In levoversion if the left eye is higher itcould be due to a LIR paralysis. Alternately, it could mean that theright eye is hypotropic and this would be due to RIO paralysis. Thus,we have narrowed down the muscles from 4 to 2.

Finally, we perform the III step in which we tilt the patient’s headto the right and then to the left. If we tilt the head to the left, the righteye will extort and the left eye will intort. This is because nervousimpulses will be sent from the semicircular canals to keep the eyes ina straight position. Now, remember the superiors are intorters. So, if theright eye extorts, it means the inferiors in that eye (LIO and LIR)work and if the left eye intorts it means the superiors of that eye(RSO and RSR) work. When this happens, in the left eye the LSO andLSR should work. Now, the LSO is paralyzed and so cannot work.This will make the LSR only work in that eye and as a balance will notbe maintained between these two muscles the left eye will move upas the LSR is also an elevator. Thus, one can diagnose the case of LSO.

If we ask the patient to tilt the head to the right, the left eye willextort and the right eye will intort. In the right eye the intorters willbe the RSR and RSO. Now the RSR is paralyzed and so the RSO willonly work and the right eye will move downwards.

Similarly, we can differentiate between the LIR and the RIO in theIII step. If we tilt the head to the left, the right eye will extort and themuscles that will work are the RIO and RIR. As the RIO is paralyzedthe RIR will only work and the right eye will move downwards.

If we tilt the head to the right, the left eye will extort and themuscles that will work are the LIR and LIO. If the LIR is paralyzedthe LIO will work and the left eye will move up.

MANAGEMENT

Occlusion

When double vision is restricted to downward gaze as in fourth nerveparalysis, one can occlude the lower third of the spectacle lens before


the paretic eye with semiopaque scotch tape. This can be performed ifthe medical condition is not suitable for surgery.

Surgery

Depending on the class of SO paralysis the surgical treatment is doneaccording to von Noorden (Table 9.1).

REFERENCES



Table 9.1: Surgical treatment of superior obliquemuscle paralysis (from von Noorden et al)

Class of SO Paralysis Surgical treatment

Class 1 Inferior oblique myectomyClass 2 Superior oblique tuck (8-12 mm); recession of

contralateral inferior rectus as a secondary procedureClass 3 Hypertropia of < 25 prism diopters; inferior oblique

myectomy. If there is hypertropia of < 25 prism diopters;inferior oblique myectomy with superior oblique tuck

Class 4 As in class 3 plus recession of ipsilateral superior rectusor contralateral inferior rectus

Class 5 Superior oblique tuck with recession of ipsilateralsuperior rectus or recession of contralateral inferiorrectus

Class 6 As in classes 1-5 but bilateral surgeryClass 7 Explore trochlea

10Abducent Nerveand its Lesions

Athiya Agarwal

INTRODUCTION

The abducent nerve (sixth cranial nerve) is a small, entirely motornerve that supplies the lateral rectus of the eyeball.1,2

NUCLEUS

The abducent nucleus is situated in the lower part of the pons, closeto the midline (Fig. 10.1). The facial nerve lies close to it and crosses itand turns around the nucleus to emerge from the brain just adjacentto the abducent nerve. Medial to the abducent nerve nucleus lies themedial longitudinal fasciculus and the pontine paramedian reticularformation (PPRF). Lateral to it lies the fifth cranial nerve and thesympathetic neuron. Just ventral to it lies the pyramidal tract.

EXIT FROM THE BRAIN

The abducent nerve exits from the brain between the pons and themedulla oblongata at the level of the pyramid. Next to it lies thefacial nerve and then comes the eighth cranial nerve.

COURSE

The abducent nerve runs from the pons towards the middle cranialfossa (Fig. 10.2). Just beyond its origin the III, IV and V nerve areabove it (Fig. 10.3). The sixth nerve passes inferior to the inferiorpetrosal sinus in an anterolateral direction and runs almost verticallyup the back of the petrous temporal near its apex. It is placed andheld here in a groove, which has a very variable appearance. Havingarrived at the sharp upper border of the bone, it bends forwardspractically at a right angle (Fig. 10.2) under the petrosphenoid ligament

Abducent Nerve and its Lesions 133

Fig. 10.1: Nucleus of the abducent nerve and the brainstem syndromes

Fig. 10.2: Course of abducent nerve


called the Gruber’s ligament to enter the cavernous sinus. It is thuspassing through a canal called the Dorello’s canal.

Cavernous Sinus

In the cavernous sinus, the sixth nerve runs almost horizontallyforwards. In the posterior part of the sinus, the nerve winds aroundthe lateral aspect of the ascending portion of the internal carotid arterythus making a second bend this time however with a lateral convexity(Fig. 10.2). Further forwards the sixth nerve lies below and lateral tothe horizontal portion of the internal carotid artery.

Superior Orbital Fissure

The sixth nerve then passes through the superior orbital fissure toenter the orbit. The nerve passes through the middle portion of thesuperior orbital fissure.

Orbit

In the orbit, the abducent nerve runs forwards and enters the ocularsurface of the lateral rectus muscle (Fig. 10.4) just behind its middleportion before dividing into 3 to 4 branches.

Fig. 10.3: Abducent nerve and its relations


CLINICAL FEATURES OF SIXTH NERVE PALSY

Deviation

In the primary position the eyeball is converged due to the unopposedaction of the medial rectus muscle.

Ocular Movements

Abduction is limited due to weakness of the lateral rectus muscle.

Diplopia

Uncrossed horizontal diplopia occurs, which becomes worse towardsthe action of the paralyzed muscle.

Head Posture

The face is turned towards the action of the paralyzed muscle tominimize diplopia.

Fig. 10.4: Abducent nerve and other nerves in the orbitIII A – Upper division of oculomotor; III B – Lower division of oculomotor; IV –Trochlear nerve; VI – Abducent nerve; LPS – Levator palpebrae superiors; SR –Superior rectus; LR – Lateral rectus; IR – Inferior rectus; MR – Medial rectus; SO –Superior oblique; IO – Inferior oblique


LESIONS

Various lesions of the abducent nerve in its course (Fig. 10.5) canproduce various syndromes. They are as follows:

The Brainstem Syndrome

A brainstem lesion of the sixth nerve may also affect the fifth, seventhand eight cranial nerves and also the cerebellum. The sixth nervenucleus has also connections via the medial longitudinal fasciculuswith the III nerve nucleus and so a lesion here produces a gaze palsy.Three syndromes can occur in the brainstem (Fig. 10.1). They are asfollows.

Millard-Gubler Syndrome

In this the lesion is ventral and involves the facial nerve and thepyramidal tract. Thus, there is a sixth nerve paresis, ipsilateral VIInerve paresis and contralateral hemiparesis.

Raymond’s Syndrome

In this syndrome the lesion involves only the sixth cranial nerve andthe pyramidal tract. Thus, the patient has a sixth nerve paresis andcontralateral hemiparesis.

Fig. 10.5: Lesions of the abducent nerve


Foville’s Syndrome

In this the lesion is dorsally. As the lesion is dorsal the areas affectedare the medial longitudinal fasciculus, the pontine paramedian reticularformation, the fifth nerve and the sympathetic neurons. Thus, thepatient has horizontal conjugate gaze palsy, ipsilateral V, VI, VII andVIII nerve palsies with ipsilateral Horner’s syndrome.

Subarachnoid Space Syndrome

Elevated intracranial pressure may result in downward displacementof the brainstem, with stretching of the sixth nerve, which is tetheredat its exit from the pons and in Dorello’s canal. This gives rise tononlocalizing sixth nerve palsies of raised intracranial pressure. Thirtypercent of patients with pseudotumor cerebri have sixth nerve paresis,besides papilledema and its visual field changes.

Petrous Apex Syndrome

The sixth nerve passes under the Gruber’s ligament in the Dorello’scanal. This makes it liable to a lesion.

Gradenigo’s Syndrome

This is due to a localized inflammation or extradural abscess of thepetrous apex following complicated otitis media. This leads to:• Sixth nerve palsy• Ipsilateral decreased hearing (eighth nerve involvement)• Ipsilateral facial pain in the distribution of the fifth nerve• Ipsilateral facial paralysis.

Pseudo-Gradenigo’s Syndrome

This is seen in two conditions:Nasopharyngeal carcinoma This may cause serous otitis media due to

obstruction of the eustachian tube and the carcinoma may subsequentlyinvade the cavernous sinus causing sixth nerve paresis.

Cerebellopontine angle tumor This may cause sixth nerve paresis withdecreased hearing (VIII nerve), VII nerve palsy, V nerve palsy, ataxiaand papilledema.

Cavernous Sinus Syndrome

In this other nerves in the cavernous sinus also are involved like thethird, fourth and fifth nerves.


Orbital Syndrome

In this proptosis is an early sign and the optic nerve may appear normalor demonstrate atrophy or edema. The ophthalmic division of thefifth nerve is involved. The third, fourth and sixth nerves are alsoinvolved. It occurs due to trauma, tumors or inflammations.

Isolated Sixth Nerve Palsy

This can also occur.

DIFFERENTIAL DIAGNOSIS

• Thyroid eye disease• Myasthenia gravis• Duane’s syndrome type 1• Spasm of the near reflex• Medial wall orbital blow-out fracture with restrictive myopathy• Break in fusion of a congenital esophoria.

MANAGEMENT

Occlusion

One can perform occlusion when double vision is present in lateralgaze in patients with mild sixth nerve paresis.

Treatment of the Cause

One should find out the cause and treat it.

Surgery

A maximal recession-resection procedure suffices in most instancesof incomplete abducens paralysis to restore a useful field of singlebinocular vision and to eliminate the head turn. If there is a completeparalysis of the lateral rectus muscle, one can perform a transpositionof the superior and inferior rectus muscles to the insertion of thelateral rectus muscle. This is called Hummelsheim’s operation (Fig.10.6). In this half the SR and LR are transposed to the area of the LR.Recession of the MR is also done. In Jensen’s operation also (Fig.10.7), the transposition is done with recession of the medial rectus. Inthis operation, the LR is split and so also the SR and IR. Then the splitportions of the SR and IR are sutured to the split portions of the LR.


Botulinum Toxin Injection

Temporary paralysis of an extraocular muscle can be used inconjunction with the transposition procedures or in isolation. Todetermine the state of recovery of the lateral rectus following a sixthnerve palsy, a tiny dose of Botulinum toxin is injected into the bellyof the overacting medial rectus muscle. This makes the medial rectusparalyzed and so the horizontal forces on the globe are more balancedand the esotropia reduced or eliminated.

REFERENCES

1. Sunita Agarwal, Athiya Agarwal, et al. Textbook of Ophthalmology 4th vol.;Jaypee, India 2003.


Fig. 10.6: Hummelsheim’s operation. 1. Half the SR and IR are transposed tothe area of the LRl; 2.Recession of the MR is also done

Fig. 10.7: Jensen’s operation. 1. LR is split and so also the SR and IR are split.Then the split portions of the SR and IR are sutured to the split portions of the LR;2. Recession of the MR is also done

11Trigeminal Nerve

Athiya Agarwal

INTRODUCTION

The trigeminal nerve1,2 is the fifth cranial nerve and is both motorand sensory. On the sensory root there is a large ganglion called thetrigeminal ganglion.

NUCLEUS

There are two portions to discuss regarding the nuclei: The first is the motornucleus and the second is the sensory nucleus. The motor nucleus isin the upper pons. The sensory nucleus extends in continuitythroughout the whole length of the brainstem and descends into theupper 2 or 3 segments of the spinal cord. The mesencephalic part isfor propioception, the pontine part is for nice sensations, and thespinal or medullary nucleus is for nasty sensations.

EXIT FROM THE BRAIN

The trigeminal nerve exits from the brain at the level of the pons.Lateral to the fifth nerve is the middle cerebellar peduncle. The motornerve emerges separately, slightly cranial and medial to its companion.

TRIGEMINAL CAVE

Together they pass below the tentorium cerebelli to the mouth of thetrigeminal cave. This is a tubular prolongation of arachnoid. Thesensory root expands into a large flat crescentic trigeminal ganglion.The motor root remains separate. The trigeminal ganglion lies in thetrigeminal or Meckel’s cave. The anterior half of the ganglion givesoff its three sensory divisions: (i) the ophthalmic division (V1), (ii)maxillary division (V2), and (iii) mandibular vision (V3). The motor

Trigeminal Nerve 141

root of the nerve has no connection with the ganglion but lies on itsdeep surface, crossing from the medial to the lateral side, to join themandibular divisions of the trigeminal nerve (Fig. 11.1). Theophthalmic and maxillary divisions pass forwards in the lateral wallof the cavernous sinus . They are wholly sensory. The mandibulardivision passes straight down from the lower part of the ganglion tothe foramen ovale. Here the motor root (Fig. 11.1) joins it.

OPHTHALMIC DIVISION

In the cavernous sinus, the ophthalmic division picks up sympatheticfibers from the cavernous plexus. These are for the dilator pupillaemuscle. It divides just posterior to the superior orbital fissure intothree branches, which pass through the superior orbital fissure toenter the orbit (Fig. 11.1).

Fig. 11.1: Ophthalmic division of the trigeminal nerve1. Lacrimal nerve; 2. Frontal nerve: (A) Supraorbital N (B) Supratrochlear N;3. Nasociliary nerve (A) Sensory root to the ciliary ganglion; (B) Long diliarynerve; (C) Posterior ethmoidal nerve; (D) Anterior ethmoidal nerve; (E) Infratrochlearnerve


Lacrimal Nerve

This is the smallest branch. It passes through the lateral portion of thesuperior orbital fissure lateral to the frontal and IV nerve and abovethe superior ophthalmic vein. In the orbit, it runs forwards just lateralto the upper border of the LR to reach the lacrimal gland. It alsosupplies the conjunctiva and skin of the lateral part of the upper lid.

Frontal Nerve

This is the largest of the three branches of the ophthalmic division. Itarises in the cavernous sinus just behind the superior orbital fissurethrough which it enters the orbit. In the superior orbital fissure, it isbetween the lacrimal nerve and the IV cranial nerve. It runs abovethe LPS and divides into two branches—a large supraorbital and asmall supratrochlear nerve.

Nasociliary Nerve

It is intermediate in size between the lacrimal and frontal nerve. Itpasses through the superior orbital fissure within the annulus tendonbetween the divisions of the third cranial nerve. In the orbit, it inclinesmedially with the ophthalmic artery above the optic nerve and belowthe SR. Thus, the nasociliary nerve, ophthalmic artery and the superiorophthalmic vein lie between the optic nerve and the SR muscle. The branchesof the nasociliary nerve are:

Sensory root of the ciliary ganglion This is given off just in front ofthe superior orbital fissure. It reaches the ciliary ganglion and doesnot synapse there. From the ciliary ganglion about 6 short ciliary nervesare given off which are sensory to the whole eyeball including thecornea but not the conjunctiva which is supplied by the lacrimal andsupratrochlear nerves.

Long ciliary nerves They are two in number and come off thenasociliary nerve. They pierce the sclera and pass in the suprachoroidalspace to supply the iris, ciliary muscle and cornea. They also carrysympathetic fibers to the dilator pupillae muscle.

Posterior ethmoidal nerve This passes through the posterior ethmoidalforamen.

Anterior ethmoidal nerve This passes through the anterior ethmoi-dal foramen. This nerve enters the anterior cranial fossa and reaches the tipof the nose as the external nasal nerve. This is important as if a patient hasherpes zoster and the tip of the nose is affected it means the nasociliary nerveis involved and that means the eye will definitely get involved. This is calledHutchinson’s rule.

Trigeminal Nerve 143

Infratrochlear nerve This is the terminal branch of the nasociliarynerve.

MAXILLARY DIVISION

The maxillary division passes through the foramen rotundum andgives off three posterior superior alveolar nerves (Fig. 11.2), a middlesuperior alveolar nerve and an anterior superior alveolar nerve. Then,it passes through the infraorbital canal and emerges as the infraorbitalnerve. A loop of nerve called the loop of Woodron connects theposterior and middle superior alveolar nerves. It also gives off a nerveto supply the lacrimal gland, which travels along the lacrimal nerve.It also gives off the zygomatotemporal and zygomatofacial nerves.

MANDIBULAR DIVISION

The mandibular division passes through the foramen ovale and givesoff first the meningeal branch, which passes back into the skull throughthe foramen spinosum. It then divides into two divisions—the anteriorand posterior division. Each in turn has some branches (Fig. 11.3).Thus, the branches of the mandibular division are:• Meningeal branch• Anterior division which in turn has:

1. Temporal branch2. Masseteric branch

Fig. 11.2: Maxillary division of the trigeminal nerve


3. Pterygoid branch4. Buccal nerve.

• Posterior division which in turn has:1. Auriculotemporal nerve2. Nerve to medial pterygoid3. Lingual nerve4. Inferior alveolar nerve.

REFERENCES



Fig. 11.3: Mandibular division of the trigeminal nerve1. Meningeal branch; 2. Anterior division ; 3. Posterior division

12Facial Nerve and

its LesionsAthiya Agarwal

INTRODUCTION

The facial nerve1,2 is the seventh cranial nerve and it is both a motoras well as a sensory nerve.

NUCLEUS

The seventh cranial nerve has three nuclei:

The Main Motor Nucleus

This lies in the lower part of the pons. The part of the nucleus thatsupplies the muscles of the upper part of the face receives corticonuclearfibers from both cerebral hemispheres. The part of the nucleus thatsupplies the muscles of the lower part of the face receives corticonuclearfibers from the opposite cerebral hemisphere only.

Parasympathetic Nuclei

These include the superior salivatory and lacrimatory nuclei. Theformer supplies the submandibular and sublingual glands and thelatter the lacrimal gland.

Sensory Nucleus

This is situated in the upper part of the medulla oblongata.

COURSE

The facial nerve exits from the brain (Fig. 7.3) at the level of the junctionbetween the pons and the medulla. Medial to it lies the VIth nerveand lateral to it lies the VIIIth nerve. The nerve then passes throughthe internal auditory meatus (Fig. 12.1). At its exit from the brain a


cerebellopontine angle tumor can affect it. In such a case the nervesaffected are the Vth, VIth, VIIth and VIIIth. The geniculate ganglionis located on the first bend of the facial nerve. This is a sensoryganglion.

A nerve starts from the geniculate ganglion called the greatersuperficial petrosal nerve. This joins another nerve called the deeppetrosal nerve, which is a branch from the sympathetic plexus aroundthe internal carotid artery. These two nerves join to become the Vidiannerve or the nerve of the pterygoid canal. This then passes throughthe Vidian canal or the Pterygoid canal and ends in the pterygopalatineganglion. This ganglion is the largest parasympathetic peripheralganglion. It serves as a relay station for secretomotor fibers to thelacrimal gland and to the mucous glands of the nose, palate andpharynx. From the pterygopalatine ganglion secretomotor fibers goto the lacrimal gland. These hitchhike on to V2 (maxillary division ofthe trigeminal nerve) and then onto the lacrimal nerve (branch of

Fig. 12.1: Course of the facial nerve

Facial Nerve and its Lesions 147

V1—ophthalmic division of the trigeminal nerve). Remember that thelacrimal gland’s tear production is due to the VIIth nerve and not due to theVth nerve.

From the geniculate ganglion the facial nerve curves downwardsand gives off a nerve called the nerve to the stapedius. If this is cutthe patient develops tinnitus. Then another nerve is given off calledthe chorda tympani nerve. This supplies taste for the anterior two-third of the tongue. The IXth (Glossopharyngeal nerve) nerve suppliesthe posterior one-third of the tongue. The VIIth nerve also suppliessubmandibular and sublingual glands.

The facial nerve then comes out through the stylomastoid foramenand gives of the posterior auricular nerve. It then goes to supply themuscles of the face by dividing into two branches—zygomatotemporaland cervicofacial. The former gives off the temporal and the zygomaticbranches. The latter gives off the cervical and mandibular branches.The buccal nerve is between these two branches. Thus, these fivenerves supply the muscles of the face and this distribution is like aclaw of a tiger and hence is called pes anserinus. The zygomatic branchsupplies the orbicularis oculi muscle.

LESIONS OF THE FACIAL NERVE

The lesions of the facial nerve are shown in Figure 12.2. They are asfollows:

Supranuclear Lesion

If the lesion is supranuclear the lower half of the face is only involvedand if it is a lower motor neuron lesion the whole half of the face isinvolved. This is because the upper half of the face has a bilateralinnervation.

Cerebellopontine Angle Tumor

Just as the VIIth nerve comes out from the brain it can get affected bythe cerebellopontine angle tumor. The patient has:• Total ipsilateral facial weakness (VIIth nerve involvement)• Decreased tearing (lacrimation involved)• Hyperacusis (nerve to stapedius involved)• Decreased taste from the anterior two-third of the tongue (chorda

tympani nerve involved)• Vth, VIth and VIIIth nerve involved with cerebellar dysfunctions.


Geniculate Ganglionitis

Geniculate ganglionitis is known as the Ramsay-Hunt syndrome. Thefeatures are:• Same findings as in cerebellopontine angle tumors except no

associated neurological deficits• May see zoster vesicles on tympanic membrane, external auditory

canal or external ear.

Fig. 12.2: Lesions of the facial1. Supranuclear lesion; 2. Cerebellopontine angle tumor; 3. Geniculate ganglionitis(Ramsay Hunt syndrome); 4. Isolate ipsilateral tear deficiency; 5. Lesion beforenerve to stapedius; 6. Lesion after nerve to stapedius; 7. Lesion after chordatympani nerve; 8. Bell’s palsy – isolated total ipsilateral facial palsy; 9. Isolatedpartial ipsilateral facial palsy

Facial Nerve and its Lesions 149

Isolated Ipsilateral Tear Deficiency

Isolated ipsilateral tear deficiency occurs in nasopharyngeal carcinomas,which affect the Vidian nerve or the pterygopalatine ganglion.

Lesion before Nerve to Stapedius

Lacrimation is normal. The other findings are:• Hyperacusis (nerve to stapedius involved)• Decreased taste from the anterior two-third of the tongue (chorda

tympani nerve involved)• Total ipsilateral facial weakness (VIIth nerve involvement).

Lesion after Nerve to Stapedius

• Decreased taste from the anterior two-third of the tongue (chordatympani nerve involved)

• Total ipsilateral facial weakness (VIIth nerve involvement).

Lesion after Chorda Tympani Nerve

Only total ipsilateral facial weakness (VIIth nerve involvement).

Bell’s Palsy

Only total ipsilateral facial weakness (VIIth nerve involvement).

Isolated Partial Ipsilateral Facial Palsy

In this only certain branches of the VIIth nerve are affected.

SUMMARY

Thus, if we understand the course of the facial nerve, we can diagnosethe level of lesion in the facial nerve.

REFERENCES



13Congenital OpticNerve Anomalies

Priya Narang, Sameer Narang, Amar Agarwal

INTRODUCTION

Congenital optic nerve anomalies are quite a common entity and areoften included in the differential diagnosis of various clinical disordersas they are often associated with visual field defects central nervoussystem (CNS) malformations and other ocular abnormalities. Athorough knowledge of the embryological development of the opticnerve entails a better understanding of the development of optic nerveanomalies.

The optic nerve develops from the optic stalk or optic pedicle. Theclosure of the fetal fissure converts the optic stalk into a roundedcord-like structure. Its cavity communicates on one side with the cavityof diencephalon and on the other side with the primary optic vesicle.The nerve fibers then grow from the ganglion cells towards the brainthrough the stalk. The optic nerve is then filled with glial tissue andfibrous septa. The sheaths of the optic nerve develop from themesoderm. The medullation of the nerve fibers which begins fromthe brain and extends up to the lamina cribrosa is nearly complete atterm. As stated above, any deviation from the normal developmentleads to congenital anomalies which are described here.

CAUSES

• Abnormal small optic disk• Aplasia• Abnormal shape of the optic disk• Bergmister’s papillae• Optic nerve head drusen (Fig. 13.1)• Myelineated nerve fibers (Fig. 13.2)• Optic disk coloboma

Congential Optic Nerve Anomalies 151

• Optic disk pit• Morning glory syndrome• Tilted disk.

APLASIA

Aplasia is a rare anomaly characterized clinically by a total blind eyewith an afferent pupillary defect, an absent optic disk and an absentretinal vasculature.

HYPOPLASIA

The optic disk hypoplasia is a sporadic condition. The affected can bemicro-ophthalmic or of normal size and usually exhibit a wide rangeof visual impairment from normal vision to severe visual loss withstrabismus or nystagmus in bilateral cases. Visual acuity is determinedprimarily by the integrity of the papillomacular bundle. The visualfields show a localized defect. The disk is surrounded by a peripapillaryhalo, bordered by a dark pigment ring called as the double ring sign.Retinal vascular tortuosity is commonly seen. Histologically opticnerve hypoplasia is characterized by a subnormal number of opticnerve axons with normal mesodermal elements and glial supportingtissue.

Some of the optic nerve hypoplasia are segmental. Apathognomonic superior segmental hypoplasia with an inferior visualfield defect occurs in some children of insulin dependent diabeticmothers. In cases of homonymous hemianopic hypoplasia, there iscongenital cerebral hemiatrophy.

Patients with periventricular leukomalacia often have a unique formof optic nerve hypoplasia characterized by an abnormally large cupand a thin neuroretinal rim contained within a normal sized disk canbe associated with intracranial and facial anomalies like septo-opticdysplasial De Morsiers syndrome, congenital hypopitutarism,hydrancephaly, arrhinencephaly, aniridia, homonymous optichypoplasia associated with congenital hemispheric aplasia, cyclopia,enchelomeningocele and hypertelorism.

De Morsier’s syndrome refers to the constellation of small anteriorvisual pathways, absence of septum pellucidum, and agenesis orthinning of the corpus callosum. MRI is the optimal noninvasiveneuroimaging modality for delineating congenital CNS malformationsin patients with septo optic dysplasia. In bilateral optic nervehypoplasia the coronal MRI shows diffuse thinning of the opticchiasma.


The detection of hypopitutarism is an essential component of theevaluation of children with optic nerve hypoplasia, because childrenwith endocrinological deficiency are at risk for impaired growth,hypoglycemia, developmental delay, seizures and death. Parentsshould be asked about the history of protracted neonatal jaundiceand previous episodes of hypoglycemia in the neonatal period.

Infants with optic nerve hypoplasia have superimposed delayedvisual maturation. Therefore infants who initially appear to be blindmay have improvement of their vision during the first several monthsof life.

Treatment

Superimposed ambylopia should be treated with a trial of occlusiontherapy children with hypopitutarism should be treated with pituitaryhormone replacement.

BERGMISTER’S PAPILLAE

The glial sheath of Bergmister envelops the posterior third of thehyaloid artery it begins to atrophy about the seventh month ofgestation, even before the main vessel atrophies. The extent of theatrophy is below the surface of the disk. If the atrophy at the disk isless complete a tuft of glial tissue may be seen thorough out the lifeover the optic disk called the Bergmister’s papillae.

MYELINEATED NERVE FIBERS

Medullation or myelineation of the optic nerve begins in the fetal lifefrom the lateral geniculate body towards the globe. Normally themyelination is completed shortly after birth at which time the myelinsheath reaches the posterior aspect of the lamina cribrosa. Themedullated fibers may be seen starting from the disk and extendingtowards the periphery (Fig. 13.2). Fundus examination shows irregularfeather-like patches which may or may not obscure the retinal bloodvessels. Rarely, isolated peripheral patches of myelination may alsooccur.

Myelination of the nerve fibers results in visual field defects.Myopia, coloboma, polycoria, keratoconus, oxycephaly and

neurofibromatosis have been associated with myelineated nerve fibers.

OPTIC NERVE HEAD DRUSEN

Deposition of hyaline like calcified material within the substance ofthe optic nerve head.Optic nerve head drusen (Fig. 13.1) can be


inherited or can be associated with heredodegenerative conditionslike retinitis pigmentosa or angioid streaks or can be following longstanding papilledema, papillitis, vascular occlusions.

Clinically has an irregular, nodular, mulberry like appearance ofthe surface of the disk. The physiological cup can be absent but venouspulsation is present there can be abnormal tortous, anomalouslybranching vessels. Disk can be pallor sometimes but will have irregularmargins. They vary greatly in size, shape and number, smaller onesoften coalesce to form larger ones.

The differential diagnosis of optic disk drusen includespapilledema with which it is often confused. Fluorescein angiographyhelps to differentiate between both the conditions which closelysimulate each other. Drusens’ exhibit the phenomenon ofautofluorescence and may stain during the late stages of angiogram.They exhibit no leakage of fluorescein from the optic nerve head whichis usually present in papilledema.

Patients with disk drusen usually remain asymptomatic althoughfew cases have been reported to develop peripapillary and macularhemorrhage. Drusens may directly compress the nerve fibers withinthe disk and cause various visual field defects like enlargement of theblind spot, arcuate scotoma or peripheral field constriction. Centralvisual acuity is usually good.

COLOBOMA OF OPTIC DISK

A coloboma of the optic disk (Fig. 13.1) results from incomplete closureof the embryonic fissure. The fissure initially closes in the middle andthen extends anteriorly and posteriorly until a small crescent at theposterior pole remains open. When the lips of the fissure fail to fuse,typical colobomas result. The coloboma of the optic nerve may occuralone or may be associated with coloboma of the iris, retina, choroidor ciliary body.

It usually occurs in two forms.

Optic Disk Coloboma in Associationwith Retinochoroidal Coloboma

This form of coloboma is more common and frequently occursbilaterally. It is characterized by a large excavation which is usuallysituated inferiorly with the normal appearing disk tissue pushedsuperiorly. It is associated with superior visual field defects.

The retinochoroidal coloboma may involve the optic nervecompletely or occasionally there is a patch of healthy tissue between


the retinochoroidal coloboma and the optic disk coloboma. Suchcolobomas are known as Bridge colobomas.

Coloboma of the Optic Nerve Entrance

These are isolated colobomas of the optic nerve wherein the diskshows an enlarged and excavated nerve head with an expanded scleralcanal. It is usually unilateral and is associated with high myopia andamblyopia. The central area of the nerve shows persistent hyaloidremnants. The blood vessels which are believed to be cilioretinal inorigin emerge like the spokes of a wheel in a radical fashion from therim of the excavation. This is known as Morning glory syndrome (Fig.13.2).

Fig. 13.1: Optic nerve head drusen

Fig. 13.2: Myelineated nerve fibers


Occasionally mild failure of closure of embryonic fissure leads tothe development of inferior crescent which is situated at the loweredge of the disk. It closely resembles the myopic crescent and is foundto occur more commonly in hypermetropic and astigmatic eyes.

MORNING GLORY SYNDROME

The morning glory anomaly is a congenital, funnel shaped excavationof the posterior fundus that incorporates the optic disk. The disk ismarkedly enlarged, orange or pink in color and typically situatedwithin a funnel shaped excavation. Surrounding the excavation is avariably elevated annular zone of altered retinal pigmentation. A whitetuft of glial tissue overlies the recessed central portion of the lesion.The blood vessels appear increased in number and arise from theperiphery of the disk. They run an abnormally straight course overthe peripapillary retina and tend to branch at acute angles. It is oftendifficult to distinguish arterioles from venules. The macula may beincorporated into the excavation called as macular capture. Computedtomography shows a funnel shaped enlargement of the distal opticnerve at its junction with the globe.

Visual acuity anges from 20/200 and finger counting. Morning glorysyndrome is more common in females and rare in blacks.

Serous retinal detachment is the most noted complication of thisanomaly 26 to 38 percent of the eyes with morning glory result inretinal detachment.

Associated with basal encephalocele with midfacial anomalies(hypertelorism, cleft lip, cleft palate, depressed nasal bridge, midlineupper lid notch).

MRI is indicated in patients with mid facial anomalies andneurological deficits because these patients are at high risk for anassociated basal encephalocele.

Treatment

superimposed ambylopia should be treated with a trial of occlusiontherapy. Patients with basal encephalocele should be evaluated forsurgical repair.

TILTED DISK

Tilted disk is caused by an oblique insertion of the optic nerve intothe globe. The upper temporal portion of the disk often lies anteriorto the lower margin. The vertical axis of the disk is directed obliquely


which gives it an oval appearance. This condition may be associatedwith visual field defects which involve the upper temporal quadrantbecause of the ectasia of inferonasal portion of the fundus. The visualfields in the congenital tilted disk does not respect the vertical meridianand it usually crosses the vertical meridian. Can be associated withthe situs inversus of the blood vessels.

Tilted disk is often found to be associated with degenerative highmyopia wherein scleral ectasia or staphyloma involve the posteriorpole temporal to the disk. This results in an oblique exit of the opticnerve.

OPTIC DISK PIT

Optic disk pit is usually seen as a small excavation along the temporalborder of the disk covering nearly one-third of the surface of thedisk. It is usually round or oval in shape and appears darker than thesurrounding disk tissue probably because of the inability to illuminatethese small deep excavations. It is usually unilateral and the disk mayappear larger as compared to the fellow eye.

In 15 percent of the cases it can be bilateral. A cilioretinal artery isfound in 59 percent of the eyes with optic disk pit.

Approximately 45 percent of the eyes with congenital optic diskpit develop serous macular elevations.

The macula demonstrates the following progression of events.Aninner layer retinoschisis cavity initially forms in direct communicationwith the optic pit an outer layer macular hole develops beneath theboundaries of the retinoschisis cavity.

An outer layer retinal detachment develops around the macularhole. This outer layer detachment ophthalmoscopically can be mistakenfor an pigment epithelial detachment, but it does not hyperflouresceon FFA.

The outer layer detachment eventually enlarges and obliteratesthe retinoschisis cavity. At this stage, it becomes clinicallyindistinguishable from a primary serous macular detachment.

BIBLIOGRAPHY

1. Amar Agarwal. Handbook of Ophthalmology; Slack USA 2005.2. David J Apple, Maurice F. RABB (3rd ed) Ocular Pathology Mosby.3. Sunita Agarwal, Athiya Agarwal, et al. Textbook of Ophthalmology 4th vol.;

Jaypee, India 2003.

14 Optic Nerve Tumors

Nick Mamalis, Garrett Smith

INTRODUCTION

Tumors of the optic nerve are relatively rare lesions. However, theselesions have significant risk for visual morbidity as well as otherproblems related to the central nervous system (CNS). Optic nerveglioma (astrocytoma) is the most common intrinsic tumor of the opticnerve. Juvenile pilocytic astrocytomas are by far the most commonoptic nerve tumor of children. Malignant gliomas of the optic nerveoccur much less frequently and are seen in adults. Meningiomas ofthe optic nerve sheath are the second largest group of tumors whichmay affect the optic nerve and occur more commonly in adults. Lastly,secondary tumors of the optic nerve may arise from direct invasionfrom intraocular malignancies, meninges, adjacent structures, as wellas distant metastases.

OPTIC NERVE GLIOMAS

Gliomas (juvenile pilocytic astrocytoma) are the most important opticnerve tumor of children, accounting for 65 percent of all intrinsic opticnerve tumors.1 Gliomas are benign neoplasms arising from theneuroglia (astrocytes and oligodendrocytes). The majority of opticnerve gliomas are of astrocytic origin. However, a few rare opticnerve gliomas arise from oligodendrocytes. The descriptive termjuvenile pilocytic astrocytoma is often used to describe this low-gradeglioma. Gliomas grow slowly, but can spread under the dura to invadelocal structures. Patients typically present before the age of 20 withprogressive visual loss, proptosis, and disk pallor with or withoutpapilledema. Management includes observation, radiation, andsurgery.


Clinical Features

Age

In 1816 Antonio Scarpa first described optic nerve tumors and notedthat the majority of his patients with gliomas were children. This facthas been substantiated in subsequent reports.1 In Dutton’s review ofgliomas of the anterior visual pathway, the mean age of presentationwas 8.8 years, with 70 percent of optic nerve gliomas occurring in thefirst decade of life, 20 percent in the second decade, and 10 percentbetween the ages of 20 and 80.1 Optic nerve gliomas are rare lesionsestimated at 5 percent of intracranial tumors and 3 percent of all orbitaltumors.2,3

Sex

Optic nerve gliomas show equal to a slight female preponderance.One study of 594 patients had 295 (50 percent) females and 299 (50percent) males.1 For gliomas confined to the optic nerve, earlier studiessuggest a slight female preponderance of about 2:1.4,5

Location

The size, growth pattern, and symptoms of the tumor depend uponthe location of the tumor. In a study of 1278 cases, 75 percent involvedthe chiasm and optic nerve, while 25 percent were confined to theoptic nerve alone.1 Of the lesions involving the chiasm, 7 percent wereconfined solely to the chiasm. Extension from the optic nerve intointraocular structures, meninges, and brain occurs in a few rare cases.6,7

It is thus helpful to divide optic nerve gliomas into two categories:orbital gliomas and intracranial or chiasmal gliomas.

Orbital gliomas vary in size and growth pattern, but are generallyslow growing benign tumors. Many orbital tumors slowly enlarge toreach a plateau, then remain unchanged for many years. Thisstabilization phenomenon is the reason that many considered theseas hamartomas. Hamartomas are a focal malformation resembling aneoplasm, but is the result of faulty organ development composed ofan abnormal mixture of tissue elements.

Chiasmal gliomas seem to be more aggressive than orbital gliomas,and a few cases have reported malignant change.8,9 Of the tumors inthe chiasm, 46 percent involved the hypothalamus or third ventricle,interfering with hypothalamic and pituitary function.1 Thus, patientswith chiasmal tumors often present with endocrine abnormalities.

Optic Nerve Tumors 159

Chiasmal tumors are also a concern because they can obstruct thethird ventricle causing intracranial pressure elevation.

Presenting Signs and Symptoms

Orbital gliomas present with more orbital manifestations, whilechiasmal gliomas demonstrate more neurological symptoms. However,both tumors share many of the same symptoms and many patientspresent with tumors involving both the orbital optic nerve and thechiasm.

Regardless of tumor location, patients may experience some degreeof unilateral visual dysfunction, visual field loss, afferent pupillarydefect, decreased ocular motility, optic atrophy, pain, headache, andnystagmus. In Dutton’s review, 88 percent of patients presented withvision loss, 26 percent presented with acuities between 20/20 and 20/40, 19 percent between 20/50 and 20/200, and 55 percent were 20/300 or worse.1 Visual field loss occurred in 63 percent of patients andan afferent pupillary defect was seen in 75 percent of individuals.

Visual loss occurs due to astrocyte proliferation within the confinesof the dura and bone in cases of intracranial lesions. Initially, thiscauses longitudinal axon bundle separation and nerve fibercompression. The compression inhibits axoplasmic transport, with littleloss of axonal conduction. Further compression leads to demyelinationand mechanical disruption of axons. Intracranial gliomas are moreconfined and compress the axon faster, producing quicker vision loss.Orbital gliomas have more room to grow causing the characteristicslow progressive visual loss, because only individual axons degenerate.Spontaneous improvements in vision have been reported.10,11 This istheorized from variations in mucoid substance and hydration, andtheir effects on the optic nerve. In some cases rapid vision loss occursdue to occlusion of the vascular supply. Gliomas affecting the opticdisk and retrolaminar portions of the nerve may compress the centralretinal vein producing optic disk swelling. The visual loss is rapidand the clinical picture may simulate optic neuritis.

Proptosis is often the chief complaint of an orbital glioma in youngchildren, occurring 94 percent of the time in orbital lesions (Fig. 14.1).1

Because the tumor arises from the nerve within the muscle cone, theproptosis is usually axial. Minimal proptosis is 2.0 to 4.0 mm rangingup to severe proptosis at 10.0 mm or more.

Nystagmus is another initial sign of both orbital and chiasmalgliomas occurring in 23 percent of patients.1 It may be vertical,horizontal, seesaw, or rotary. Pain or headaches, and limited ocularmotility are other common symptoms of both types of gliomas.


On fundoscopic examination, 59 percent of patients demonstratedsome degree of optic atrophy and disk pallor (Fig. 14.2). Disk swellingpresents more frequently in orbital gliomas with a 48 percent occurrencerate.1 In chiasmal tumors, disk swelling occurred 22 percent of thetime, and was often bilateral, due to increased intracranial pressure.Optociliary shunt vessels are occasionally seen with optic nervegliomas, however they are far more common in optic sheathmeningiomas.

Other late and infrequent orbital glioma signs are venous stasisretinopathy with iris neovascular glaucoma, anterior segment ischemia,and hemorrhagic glaucoma from retinal vascular occlusion.

In chiasmal gliomas, 27 percent of patients had third ventricleinvolvement causing increased intracranial pressure and 26 percentreported hypothalamic or endocrine abnormalities.1,12 The endocrineabnormalities included obesity, diabetes insipidus, panhypo-pituitarism, dwarfism and precocious puberty.

Association with Neurofibromatosis

Several studies have published a 15 to 21 percent occurrence rate ofoptic gliomas in neurofibromatosis patients. A study of 2186 publishedcases of patients with optic gliomas demonstrated 29 percent of themto have neurofibromatosis.1 Patients presenting to doctors with café-

Fig. 14.1: Child with an optic nerve glioma of the left eye demonstratingproptosis with moderate inferior displacement of the left globe


au-lait spots and diagnosed with neurofibromatosis, should haveregular ophthalmic examinations. Neurofibromatosis type 1 (NF-1)patients commonly develop multiple CNS astrocytomas and theselesions show a predilection for the orbital optic nerve and chiasm.13

NF-1 lesions tend to be multifocal and more extensive along the opticpathways than in patients without NF-1. Patients with bilateral opticgliomas usually have NF-1.14 However, the incidence of visualsymptoms and progressive neurologic deficits was lower among thosepatients with NF-1.

Radiographic Findings

On plain orbital radiographs 65 percent of optic gliomas can bevisualized mainly through enlargement of the optic canal.1 The classicradiographic findings are enlargement of the optic foramen and J-shaped excavation of the sella turcica. The optic canals are usuallysymmetrical, and a 1.0 mm difference in the diameters or a verticalheight of 6.5 mm or more is considered pathologic.

Computerized tomography scans are more accurate, especially fororbital lesions. The tumor usually appears as a well-defined spindleor rounded shaped enlargement of the optic nerve.15 Kinking of thenerve is a characteristic finding in orbital gliomas, due to elongationof the nerve from secondary axial growth and downwarddeflection.15,16

Fig. 14.2: Fundus examination of the same childshowing diffuse atrophy of the optic nerve


Fig. 14.3: Axial MRI scan of a patient demonstrating a diffuse, fusiformenlargement of the optic nerve within the nerve sheath

In evaluating anterior pathway lesions CT and Magnetic ResonanceImaging are equivalent.17 However, for chiasmal, hypothalamic, andoptic tract lesions MRI is superior to CT, because in CT scans thetumor images are isodense to brain tissue.17,18 MRI differentiates tumortissue from normal brain and neural structures better, thereby allowingimproved diagnosing and monitoring. However, microscopic extensionof the tumor cannot be detected. MRI has several other advantagesover CT. MRI does not expose young children to ionizing radiation,allowing repeat serial examinations and it avoids scatter artifact nearbone.19

On T2-weighted images, gliomas are hyperintense compared tonormal optic nerve. Therefore, T2 weighted images is the best fordemarcation of tumor borders (Fig. 14.3).20 Arachnoidal gliomatosisin neurofibromatosis patients can be visualized on T2-weighted axialMRI studies as an area of high-signal intensity (due to a high watercontent in the myxomatous tissue) surrounding a linear core of lowersignal intensity.16,21 Gliomas in T1-weighted images are slightlyhypointense compared to normal optic nerve (Fig.14.4). T1-weightedimage is best for demonstrating tissue composition, characterizingnecrosis and mucinous degeneration.20

Histopathology

Gross Appearance

Optic nerve gliomas are typically contained within the dura (Figs 14.5Aand B). The dura is stretched and thin, but usually intact. Typicalgliomas appear tan to dusky red from the vascular congestion withinthe tumor. Orbital gliomas are characteristically fusiform, with the


Fig. 14.4: Sagittal MRI scan demonstrating sausage-likeenlargement of the optic nerve secondary to a glioma

Fig. 14.5B: Low-power photomicrograph of the same patient demonstrating anormal optic nerve to the left with an intact sheath around it. There is an enlargementof the nerve itself secondary to the glioma with multiple large cystic spaces withmyxomatous type degeneration (hematoxylin-eosin × 10)

Fig. 14.5A: Gross specimen demonstrating a relatively normal optic nerve on theleft with disuse enlargement of the nerve itself within the intact sheath secondaryto glioma


borders of the tumor difficult to delineate. Thus, it is helpful to obtaincross-sections at the end of each specimen.22 Gliomas may also invadethe arachnoid and pia, and extend through the subdural space. Thispattern occurs more often in neurofibromatosis patients.23 The nerveitself may be of normal thickness, but the overall diameter may beincreased because of the perineural component. Cross-sections throughthe middle portion show the whitish nerve enlarged and surroundedby a cuff of arachnoidal tissue, which is then covered by stretcheddura.

Microscopic Findings

Most optic nerve gliomas consist of elongated, spindle-shaped,pilocytic (hair-like) astrocytes (Fig. 14.6). Some researchers thus usethe term juvenile pilocytic astrocytoma to differentiate them fromother intracranial astrocytomas in older patients.24 These astrocyteshave a benign histological appearance rarely demonstrating mitoticfigures or malignant degeneration.22 The nuclei are usually uniformand oval with some being hyperchromatic (Fig.14.7). The cytoplasmis extended and contains glial filaments visible with special stainssuch as GFAP.25 These spindle-shaped astrocytes are fairly cohesiveand damage the optic nerve by forming intersecting bundles that causeaxon separation or compression of the nerve.

The most distinctive and frequently encountered degenerativechange found in optic nerve gliomas is the Rosenthal fiber.22 Rosenthalfibers are elliptical eosinophilic swellings found within astrocyte cellprocesses and surrounded by hyalinized connective tissue (Fig.14.8).These fibers consist of electron-dense granular material and glial

Fig. 14.6: Low-power photomicrograph of a juvenile pilocytic astrocytoma(hematoxylin-eosin × 100)


filaments. Foci of calcification from axonal debris commonly appearin the fiber.

Vascular proliferation and atypia are frequently seen. These vesselsare located either in the pial septa or between bundles of astrocytes.Periodically, enlarged congested sinusoidal vessels are encountered,but hemorrhagic necrosis rarely occurs.

Pale staining areas that appear microcystic on hematoxylin-eosinstaining are frequently interspersed among the astrocytes. With specialstains, the microcystic spaces can show mucosubstance (myxomatous

Fig. 14.7: Moderate power photomicrograph demonstrating a low-gradeastrocytoma of the optic nerve (hematoxylin-eosin × 200)

Fig. 14.8: Moderate power photomicrograph demonstrating multiple eosinophilicstaining cytoplasmic inclusions consistent with Rosenthal fibers (hematoxylin-eosin × 250)


glioma) from mucin-producing cells that are present in the area. The“microcysts” are not intracellular but are extracellular accumulationsof a mucicarmine-negative mucoid substance that stains with periodicacid-Schiff (PAS) and acid mucopolysaccharide. It is believed thatastrocytes produce this mucoid hydrophilic material that alsocontributes to tumor enlargement.22

Older gliomas become fibrotic with lipoidal histiocytes and thick-walled fibrotic blood vessels suggestive of an angiomatous lesion,thus, making older gliomas more difficult to recognize.

Optic nerve gliomas have two distinct growth patterns: perineural andintraneural.26 In the perineural pattern, more of the perimeterastrocytes proliferate to widen the epipial-subarachnoid space withinthe intact dura while thus compressing the residual optic nerve as acentral band. This circumferential tumor tissue consists mostly ofproliferating astrocyte nests, intermingled with meningothelial cells,fibroblasts, and fibrovascular arachnoidal trabeculae, with mucinousand microcystic degeneration. Studies by Stern et al demonstratedthese findings and they proposed the term arachnoidal gliomatosis(Fig.14.9).26 Perineural growth often involves more of the opticpathways, because the perimeter astrocytes proliferate and can tunnelalong the nerve under the dura. This perineural growth is associatedwith neurofibromatosis type 1 patients.16,26 One study observed 94percent of glioma patients with perineural growth also hadneurofibromatosis.16

The intraneural growth pattern predominates in patients withoutneurofibromatosis.26 In this pattern, the optic nerve enlarges insteadof being compressed. Intra-axial astrocytes proliferate causing

Fig. 14.9: Low-power photomicrograph demonstrating proliferation of the low-grade astrocytoma from the optic nerve to the area underlying the sheathdemonstrating arachnoid gliomatosis from a patient with neurofibromatosis(hematoxylin-eosin × 50)


expansion of fibrovascular trabeculae with slight cystic degeneration.The increasing nerve diameter crushes the subarachnoid space andfuses the pia mater to the arachnoid and dura.1

In both types of growth patterns the optic tumor enlarges byproliferation of neoplastic glial cells, accumulation of extracellular PAS-positive mucosubstance secreted by the astrocytes, reactive gliosis,meningeal hyperplasia, and congestion within dilated blood vessels.Growth is usually slow, but accelerated expansion can result fromcystic degeneration or intralesional hemorrhage. The majority ofgliomas are benign and enlarge by bulk local growth causingdemyelination and compression of optic nerve fibers. However,gliomas are true neoplasms and can tunnel under the dura extendingalong optic tracts and infiltrate the leptomeninges or intraocularstructures.9,27 A few rare gliomas can undergo malignant evolutionand spread throughout the cerebrospinal fluid.28,29

Gliomas and meningiomas of the optic nerve usually producesimilar symptoms. Therefore, identifying which type of lesion thepatient has is important. Current imaging and ultrasound techniqueshave become excellent at distinguishing the type of lesion the patienthas, but when there is doubt many clinicians still advocate biopsy.However, even on biopsy confusion may arise. Possible reactiveproliferation of meninges overlying the glioma making possible themisdiagnosis of meningioma if a very superficial biopsy of the opticnerve is done.

Management

Defining clear-cut guidelines for correct management of optic gliomasis difficult, because the natural course of gliomas is variable. Reportedstatistics and treatments results vary considerably causing muchcontroversy to exist over the proper management of optic gliomas.

A study by Wright and McDonald30 showed that in half of theirpatients, the tumor appeared to stop growing without treatment. It isthought that in this group the tumor was stable upon presentation orslowly enlarged to reach a plateau remaining unchanged for manyyears. In the other half of the patients, the glioma continued growing,resulting in clinical signs and symptoms that required surgical removal.This study shows the dilemma of whether to surgically intervenecausing blindness in that eye or to just follow the tumorradiographically and maintain partial vision. If the tumor appearsstable it is worth watching, but if the tumor progresses intracranially,it can be deadly.


If a patient presents with an optic glioma that appears to be fairlyasymptomatic and confined to the orbit, current thought is to followthe patient without treatment.1 Because many studies have shownapproximately half the gliomas plateau and remain dormant, withsome cases of vision actually improving later on.30,31 Serial CT or MRIscans, pupillary reactions, visual acuity, and visual field examinationsshould be done to monitor tumor growth. If the tumor enlarges tocause blindness, severe proptosis, or pain, then complete removal bylateral orbitotomy is warranted.32 The risk of just monitoring gliomasis that some can spread throughout the CSF invading distant areas. Afew rare gliomas undergo malignant evolution.8 Kocks reported achild who developed lumbar spinal metastases from a chiasmalglioma.33 However, the majority of gliomas grow slowly over monthsto years and spread by local enlargement. If on radiographic scans,the tumor shows extension along the intracranial portion of the nerveand threatens the chiasm, then surgery is also recommended. Oncethe tumor extends to the optic chiasm the risk of death rises to about28 percent.1 Surgical intervention at this point does not improvesurvival, and has significant visual morbidity and potential mortality.

Some research suggests a short-term benefit from radiotherapy indoses exceeding 4500 cGy for chiasmal and midbrain tumors,11,34 butoverall survival and ultimate recurrence show no benefit toradiotherapy.1,35 This raises the question as to whether radiotherapyis worth the side effects, because radiation in children has manypermanent adverse effects on the CNS and endocrine function.36

Among 511 patients treated with radiotherapy and followed for 10years, 69 percent demonstrated stable vision, 42 percent showed tumorprogression, and 28 percent died from the disease. In contrast to thetreated group, 203 similar patients were followed without treatmentand showed comparable results; 77 percent demonstrated stable vision,42 percent showed tumor progression, and 29 percent died.1 In astudy by Packer et al they advocated that chemotherapy couldsignificantly delay the need for radiation in children.14 Yet, there islittle published data on the role of chemotherapy.

Although optic gliomas are benign neoplasms they can result insignificant morbidity and mortality. Therefore, the clinical approachto these tumors must be vigilant, with attentive observation andaggressive intervention when necessary.


MALIGNANT GLIOMAS OF THE OPTIC NERVE

Malignant astrocytomas of the optic nerve are a rare, but aggressiveand deadly disease. The tumor arises from malignant astrocyteslocated in intracranial optic pathways and rapidly spreads to invadenumerous structures. Patients typically are middle-aged adults thatpresent with decreased vision, visual field loss, retro-orbital pain,and disk swelling. Most patients progress to blindness and deathwithin a year.37

Clinical Features

In contrast to benign gliomas that occur in children, malignant gliomasare a disease of middle-age. In Dutton’s review the average ofpresentation was 47, with patients ranging from six to eighty.1

Malignant optic gliomas show a male preponderance, with 65 percentoccurring in males, and 35 percent occurring in females.

Malignant gliomas of the optic nerve arise from malignantastrocytes that originate in intracranial optic pathways.37 Rarely, itarises in the orbital optic nerve. Malignant gliomas rapidly spreadanterior and posterior to involve the optic nerve, chiasm, optic tracts,hypothalamus, third ventricle, thalamus, temporal and occipital lobes.

The clinical course is unilateral visual loss that progresses toblindness and death in an average of 11 weeks, but can range up to 60weeks.1 The malignant astrocytes typically attack one side, thenrapidly spread through the chiasm to involve both optic nerves. Atpresentation 64 percent of patients have bilateral visual loss. The finalvisual acuity reported in a study of 22 patients showed that in the lessaffected eye only 23 percent had vision of 20/400 or better, while 63percent were NLP. In the more affected eye 86 percent were NLP.Visual field defects occurred in 94 percent of patients.1

On initial presentation normal optic disks are often seen, but withinweeks the disk progressively swells. If the patient lives long enoughoptic atrophy ensues.

Malignant gliomas typically arise intracranially or in the chiasmand generally affect intracranial optic pathways. Thus, neurologicalsymptoms are more common than proptosis. Neurological signsinclude convergence and gaze abnormalities, paresthesias, partialophthalmoplegia, seizures, confusion, and hallucinations.Hypothalamic involvement usually occurs in the final stages and causesmany of the deaths.37


Retro-orbital pain is a common symptom. The visual loss and retro-orbital pain often lead to an initial diagnosis of optic neuritis. Rapidand progressive visual loss should include radiological imaging.

Radiology

Plain orbital radiographs rarely reveal malignant gliomas.Computerized tomography provides a 79 percent chance of disclosingthe tumor on initial examination.1 Images portray an enlarged chiasmand optic nerves. Few reported cases have used MRI, but MRI hasrevealed the tumor in all cases.38,39

Pathology

Histological examination is consistent with malignant astrocytomashowing atypical pleomorphic astrocytes with numerous mitoticfigures. Secondary vascular and endothelial proliferation can also befound.40 The malignant cells encircle and compress the optic nerveinhibiting axoplasmic transport and capillary perfusion, causingdemyelination and axonal degeneration. The neoplastic cells usuallyextend under the pia along the optic pathways or directly within thebrain substance. The tumor can spread to invade the orbit,hypothalamus, third ventricle, basal ganglia, or intraparenchymalbrain.

Prognosis

Malignant gliomas are a sad and devastating disease with the overallmortality rate of 97 to 100 percent with a mean survival of 8.7 monthsfollowing diagnosis.1 Some patients treated with 5000 to 6000 cGYradiotherapy showed temporary visual acuity improvements andslightly prolonged life, but ultimately died from the disease. Advancesin cancer research will hopefully led to better treatments.

OPTIC NERVE MENINGIOMAS

Meningiomas are the second most common optic nerve tumor, aftergliomas.41 Meningiomas are benign neoplasms arising frommeningothelial cells typically in the arachnoid. Patients generally aremiddle-aged adults and present with decreased vision, visual fieldloss, proptosis, disk atrophy, disk swelling, and later on optociliaryshunt vessels. Meningiomas grow slowly, but are invasive andinfiltrate surrounding structures. Management includes conservativemonitoring, radiotherapy, and surgery.


Clinical Features

In contrast to gliomas, meningiomas occur later in life. In Dutton’sreview of optic nerve meningiomas, a study of 256 patientsdemonstrated the average age of presentation to be 40.8 years.41 Theaverage age for males was 36, and the average age for females was42. Even though the average age for females was older, meningiomasshow a slight female preponderance at 61 percent female and 39 percentmale. Approximately 4 to 10 percent of meningiomas occur in childrenand tends to be more aggressive.22,41 Therefore, meningiomas shouldstill be included in the differential diagnosis of a lesion causingproptosis and progressive visual loss in a child. Similar to gliomas,there is a proven higher incidence of meningiomas in patients withneurofibromatosis.42

Researchers classify optic nerve meningiomas into three typesbased on tumor origin. Primary tumors if they originate from themeninges in the optic nerve and secondary tumors if they originatefrom cranial meninges and then extend into the orbit. Approximately90 percent of meningiomas affecting the optic nerve are secondary,extending from the olfactory groove and sphenoid ridge.43,44 A thirdrare type, ectopic (extradural) arise from congenitally displacedmeningothelial cells along the floor or roof of the orbit.

Signs and Symptoms

The signs and symptoms of meningiomas depend upon the originand location of tumor growth. For ease of understanding, meningiomasaffecting the eye can be divided into four groups depending uponlocation: (i) dura restricted, (ii) orbital, (iii) intracanalicular, and(iv) secondary. The natural course of meningiomas is unpredictable,because they can invade any surrounding structure. Therefore,different tumors share many of the same clinical and pathologic signs.Ninety-five percent of primary meningiomas have unilateralinvolvement, but 5 percent are bilateral.41 The bilateral meningiomastypically arise within the optic canal or chiasm (intracanalicular).41,43

The most common symptom of all meningiomas is gradual visionloss occurring over one to five years. A study of 380 patientsdemonstrated 96 percent to have decreased vision; with 45 percentpresenting with acuities between 20/20 and 20/40, 31 percent between20/60 and 20/400, and 24 percent with counting fingers or worse.41,45

The second most common symptom was visual field loss occurringin 83 percent of patients.41,46 Peripheral constriction was the mostcharacteristic visual field loss. Central, centrocecal, paracentral


scotomas, and increasing blind spot visual field losses also occurred.Decreased color vision was reported in 73 percent of the patients.Early or rapid vision loss occurs in dura-restricted meningiomas. Thesemeningiomas grow similar to a glioma, and remain confined withinthe dura. As the meningothelial cells proliferate within the subduralspaces, the tumor begins compressing the optic nerve and inhibitsaxoplasmic transport. Further compression leads to demyelinationand mechanical disruption of axons. Similarities to gliomas also occurwhen the meningioma infiltrates the nerve and widens the septa.

More characteristic slow visual loss occurs when the meningiomapenetrates the dura and grows outside of the dura (orbitalmeningiomas). In this situation, meningothelial cells proliferate formany months to years within the orbit and the tumor becomes verylarge before compressing the optic nerve. The tumor begins to slowlypush on the posterior pole of the globe causing axial proptosis,hyperopia, and striae. Axial proptosis is often the presenting symptomof meningiomas and occurred in 59 percent of the study patients.41 Inthis situation, when the tumor enlarges outside the dura, it can impingeupon the extraocular muscles limiting ocular motility. Forty-sevenpercent of study patients complained of limitation of ocular motility.The tumor infrequently encroaches on one of the cranial nerves, causingcranial nerve palsy.44 In dura-restricted meningiomas, as the tumorenlarges it impinges and stiffens the optic nerve causing a mechanicalrestriction of extraocular muscle function.

Disk swelling is an early finding in 48 percent of patients of alltypes.41 Disk swelling occurs due to compression of the central retinalvein and meningeal vasculature or spread of tumor cells to the anteriorend of the perineural space, with interference of disk circulation. Ascompression of the optic nerve progresses the incidence and degreeof optic atrophy increases. Forty-nine percent of patients progress todevelop optic atrophy.

The classic pathognomonic triad for meningiomas of gradualunilateral vision loss, optic atrophy, and optociliary shunts (Fig. 14.10)occurs in 30 percent of patients.41 Imes et al47 followed the developmentof optociliary shunts over eight and a half years in a woman with anoptic nerve meningioma. The first two years the woman had chronicdisk swelling and congestion of the central retinal vein. After twoyears, Imes observed the dilation of regressed, but vestigeal,retinociliary anastomoses that were present in earlier embryonicdevelopment. The prolonged inhibition of retinal vein circulationre-established the flow of blood from retinal veins through optociliaryshunts into the choroidal circulation. Then as the optic atrophyworsened in the woman, the shunts regressed over the years.


Meningiomas affecting the optic canal or chiasm (intracanalicular)may simulate atypical retrobulbar neuritis with decreased visual acuityand optic atrophy. Proptosis and disk edema are rarely seen. Tumorsin the sphenoid ridge may also affect the nerves to the extraocularmuscles resulting in strabismus as a presenting sign.

Radiology

Plain orbital radiographs rarely see meningiomas. Cases ofhyperostosis of neighboring bone will show up, but these are rare.48

Computerized tomography has revolutionized diagnosing optic nervetumors, with visualization of 97 percent of meningiomas.41 CT scansshould be obtained before and after iodinated contrast mediuminfusion. Thin sections (1.5 to 3 mm) should be taken to demarcatetumor edges. Dura-restricted meningiomas often appear as a well-defined smooth tubular enlargement of the optic nerve.48 The majority(64%) of meningiomas shows this diffuse tubular thickening of theoptic nerve.49 Orbital tumors growing outside the dura show globularperioptic or irregular and serrated enlargement, unlike dura-restrictedtumors that demonstrate a fusiform shape.48,49 The dura-restrictedtumors are commonly confused with gliomas, because they both areensheathed by the dura. Helpful findings are calcifications, which areusually present in meningiomas and not typically found in gliomas.50

Another important radiographic sign helpful in diagnosingmeningiomas is tram tracking.41 In tram tracking the optic nerve canbe seen as a central black line through the whitish mass (Fig. 14.11).Tram tracking, however, may also be visualized in inflammatory

Fig. 14.10: Fundus photograph of the optic nerve from an elderly female patientdemonstrating optociliary shunt vessels with atrophy of the nerve


perioptic pseudotumor and other diffuse sheath thickenings.51 Incoronal views the denser and thickened optic nerve sheath appearsas a dense circle around the more radiolucent optic nerve.

Magnetic resonance imaging offers more precise and sensitivedetection of intracanalicular or intracranial extension of meningiomasthan CT.48,52 T1-weighted images should include fat-suppressed fine-cut axial and coronal images with and without gadolinium enhance-ment. The T1-weighted images disclose the characteristic tram-trackappearance of the optic nerve in meningiomas. Axial and coronal T2-weighted images provide the most sensitive method of determiningthe extent of tumor involvement.

An additional imaging technique called OctreoScan is used tosupport and follow the diagnosis of meningiomas. OctreoScan(Indium-111 pentetreotide) is a radio-labeled ligand that binds to thesomatostatin receptors in meningiomas. The binding is highlysensitive, but not very specific because other classes of tumors alsobind somatostatin. OctreoScan is therefore helpful in following tumorprogression in cases of observation or tumor treatment response.52

Histopathology

Meningiomas can arise from any of the different cells that comprisethe meninges (Fig. 14.12). However, current researchers believe themajority of meningiomas arise from the meningothelial cap cells foundin arachnoid villi.41,42 Arachnoid villi are smaller and similar to arach-noid granulations (grape-like tufts of arachnoid that penetrate duralvenous sinuses and affect transfer of CSF to the venous system).Arachnoid villi are collected along the intraorbital and canalicular

Fig. 14.11: CT scan of the eye and orbit showing a diffuse meningioma of thenerve anteriorly with the “tram-track” sign


portions of the optic nerve and also along the sphenoid ridge,tuberculum sellae, olfactory groove, and other areas of the meninges.

Neoplastic meningothelial cap cells are spindle or oval shaped andform densely packed concentric whorls with psammoma bodies (Figs14.13A and B). Psammoma bodies are calcifications that develop inthe whorl centers from hyalinization and deposition of calcium salts(Figs 14.14A and B). This pattern is the meningothelial pattern and isthe most idiosyncratic degenerative change found in meningiomas.Meningiomas rarely show mitotic figures or malignant degeneration.22

Cells from the arachnoidal trabeculae of the meninges are ofmesodermal origin and can proliferate to cause fibroblasticmeningiomas. This type may metastasize.41 A combination ofmeningothelial and fibroblastic is called the transitional pattern.Meningiomas are benign neoplasms that grow slowly over months toyears. Similar to gliomas, meningiomas can tunnel in the subduralspaces traveling along the optic pathways and infiltrate intraocularstructures. However, unlike gliomas, meningiomas are invasive andcan penetrate the dura to invade adjacent orbital structures, such asthe extraocular muscles, sclera, or bone.22 Optic nerve meningiomasarising in the orbit can spread posteriorly through the optic canal tothe chiasm or into the middle cranial fossa. At present, it is thoughtthat meningiomas do not invade the brain or pituitary, and it appearsmeningiomas have little effect on the pituitary-hypothalamic axisor increasing ICP.42,44,53 Meningiomas can infiltrate the bone byentering the haversian canals and initiate hyperostosis and bonyproliferation.54

Fig. 14.12: Gross photograph of an optic nerve sheath meningioma


Fig. 14.13B: Medium-power photomicrograph of a meningioma showing the spindlecells with a concentric whirl-type arrangement in the center (hematoxylin-eosin ×200)

Fig. 14.13A: Low-power photomicrograph demonstrating nests or whirls ofmeningothelial cells underlying the optic nerve sheath which is to the left(hematoxylin-eosin × 100)


Fig. 14.14A: Medium-power photomicrograph of a meningioma demonstratingcells with a round nucleus and an eosinophilic staining cytoplasm with a smallpsammoma body in the center (hematoxylin-eosin × 200)

Fig. 14.14B: Higher power photomicrographs showing a large, calcified,hyalinized, psammoma body (hematoxylin-eosin × 250)


Management

The management of optic nerve meningiomas is controversial becausetheir course is unpredictable. Traditional management includesobservation, radiotherapy, and surgery. Traditionally, if a patientpresents with the tumor confined to the orbit and visual acuity betterthan 20/40, observation was recommended.46 Observation includesophthalmic examinations and CT or preferably MRI scans every sixmonths. If visual acuity is progressively lost below 20/40, the visualfield is constricting, or imaging scans show dangerous growth thepatient is encouraged to undergo radiotherapy for preservation ofvision.46,52 If the eye is totally blind and the meningioma confined tothe orbit then the patient can choose to monitor the tumor or surgicallyexcise it. If the meningioma is spreading posterior or enlarging andcausing proptosis then total removal should be performed.

Because of the characteristic slow growth and benign pattern ofprimary optic nerve meningiomas, the overall tumor-related mortalityrate is 0 percent according to Dutton’s major review.41 This factcoupled with the risks of radiation or surgery are the reasons manyresearchers advocate observation in patients over 40. The disadvant-ages to sole observation is the possible risk of tumor spread. Of 228orbital lesions only 20 percent showed posterior extension.41 However,tumors originating in the canal or chiasm have a 38 percent chance ofcontralateral involvement.52

The most obvious disadvantage of simple observation is gradualvision loss. Kennerdell et al showed that of 39 patients that did notreceive treatment of any kind, not one maintained good visual acuityfor more than four years.46 This is in striking contrast to patientstreated with radiotherapy where 73 percent of them had improvedvision.41

Radiotherapy is the most promising treatment modality becauseof its ability to inhibit tumor growth and restore vision.46,55 Olderradiation treatments were less precise and exposed the chiasm,contralateral optic nerve, and surrounding tissues to ionizing radiation,causing optic neuropathy and secondary malignancies. Leber et al56

studied the dose to damage relationship of older modalities. Theyfound that the patients receiving less than 10 Gy per day had noincidences of optic neuropathy. 26.7 percent of patients receiving 10to 15 Gy developed sequelae and 77.8 percent of patients receivinggreater than 15 Gy developed sequelae. The newer conformalradiotherapy is much more precise and attains an improved therapeuticratio. The accuracy of computer-guided stereotactic radiotherapy only


exposes the patient to 1.8 Gy.52 This explains why many currentresearchers advocate radiotherapy as primary management in all opticnerve meningiomas as well as adjuvant treatment for incompletelyresected tumors.46,55,57,58

A few successful therapeutic surgical interventions have beenreported in tumors confined to the anterior or middle third of theoptic nerve.46,52,59-61 However, most surgical intervention results inblindness, typically attributed to ischemia of the optic nerve.46,52 Inblind eyes surgical excision of the tumor is warranted if the tumorthreatens, the optic canal, chiasm, or intraocular structures. Surgicalremoval is also indicated in blind eyes if the enlarging tumor causespain or proptosis.

Although optic nerve meningiomas are benign neoplasms, theycan result in blindness. Many technological advances have helpedpatients maintain their vision, but the clinical approach must beattentive and when necessary aggressive treatment implemented.

SECONDARY OPTIC NERVE TUMORS

The majority of tumors involving the optic nerve are from secondarymalignancies. Only 18 percent of tumors arise within the optic nerveitself, while 82 percent invade the nerve secondarily.62 There are fourmain routes of invasion into the optic nerve: direct extension fromthe eye, meninges, adjacent structures, and blood-borne metastaticinvasion via the ophthalmic artery. Ginsberg et al63 presented a reviewof 117 cases of secondary optic nerve tumors. They found 39 percentto arise from intraocular tumors, 33 percent from blood-borne tumorseeding, 20 percent from meningeal tumors, and 8 percent invadedfrom adjacent structures.

Extension from the Eye

The most common secondary optic nerve malignancy is fromintraocular structures.62 Retinoblastoma and uveal melanomaconstitute the majority of secondary intraocular tumors.

Retinoblastoma has been known for many years to invade the opticnerve, with 26.7 percent of patients with retinoblastoma in a masseye and ear study showing extension into the optic nerve.62 The tumoris usually limited by the lamina cribrosa, but may extend past it toinvade the chiasm or brain.64 Predisposing factors to nerve invasioninclude elevated intraocular pressure, glaucoma, tumor seeding intothe vitreous, and necrotic retinoblastoma.65 The prognosis significantlyworsens once the tumor progresses beyond the lamina. Kopelman


et al66 reported that the most dangerous risk factor of retinoblastomawas penetration of the coats of the eye, and the second most significantrisk factor was the degree of optic nerve invasion.

Uveal melanomas invade the nerve less than retinoblastoma, with6.5 percent of uveal melanomas invading the optic nerve.62 The diffusemelanomas have a more malignant cell type than typical nodularmelanomas. Thus, diffuse melanomas are more aggressive at invadingthe optic nerve and carry a worse prognosis. Juxtapapillary melanomascan invade the nerve by direct extension causing hyperemia and diskedema. The lamina cribrosa generally limits the tumor growth, butposterior extension into the orbit, chiasm,65 and brain67 have beenreported. Weinhaus et al68 on univariate analysis found a directcorrelation between tumor death and the degree of optic nerveinvasion. Predisposing factors for invasion include elevated intraocularpressure, juxtapapillary location, glaucoma, and necrotic tumors.

Blood-Borne MetastasisHematopoietic malignancies involving the optic nerve includeleukemia, lymphomas, and myeloma. In most forms of leukemia theoptic nerve and nerve head become infiltrated with abnormal whiteblood cells. Children with acute lymphoblastic leukemia are the mostaffected with 13 percent of patients having optic nerve invasion.69 In384 autopsy specimens, Kincaid et al70 found 82 percent of patients tohave ocular involvement. Unilateral or bilateral visual loss is the mostcommon clinical symptom. Disk swelling, as well as pallor, splinterhemorrhages from infiltration, and increased intracranial pressureoften occur. Histologically, perivascular and discrete tumor infiltrationcan be seen. Combined intrathecal chemotherapy and localizedradiotherapy have improved visual function in some cases.71

A few cases of Hodgkin’s and Non-Hodgkin’s lymphomasinvolving the optic nerve have been reported.62 Invasion into the opticnerve occurs from both chronic systemic lymphoma and CNSlymphoma that invades via the meninges. Multiple myelomaoccasionally invades the eye, but only one case of optic nerve invasionhas been reported.72

Solid tumors that metastasize to the eye and optic nerve are rareand typically occur in parallel with widespread systemic metastasis.In Ginsberg’s review of primary metastatic sites to the optic nerve,breast cancer was the most recurrent distant tumor at 33 percent.Lung cancer followed second at 11 percent and stomach third at6 percent. Others included pancreas 3 percent, mediastinum 3 percent,skin 3 percent, melanoma 2 percent, uterine 2 percent, and ovarian at2 percent.63


Extension from the Meninges and Brain

Neoplastic cells gain access to the optic nerve by anterior progressionthrough the optic canal via the subarachnoid space. Neoplasmsentering the nerve by this route include primary intracranial tumors(meningial carcinomas, reticuloendothelial sarcomas) plus secondarymetastatic tumors to the CNS, which include lymphomas, melanoma,and myeloma.65 The course of these neoplasms is variable dependingon the aggressiveness of the tumor. Slow growing tumors can spreadanteriorly producing papilledema and visual dysfunction after thedisease is advanced. Aggressive, rapidly proliferating neoplasmsinvade the axonal bundles, causing early visual loss and disk edema.The prognosis is poor once visual loss occurs from metastasis, withsurvival less than two years.73 Palliative treatment consisting ofchemotherapy and radiation has resulted in transient improvementin visual function in some cases.74

Primary tumors from the CNS (ependymoblastoma, pituitaryadenoma) rarely invade the optic nerve, but will commonly compressthe optic nerve causing a neuropathy.62

Extension from Adjacent Structures

Tumors arising in the orbit, nasal sinuses, and nasopharynx generallycompress the optic nerve instead of invading it. Visual field loss,proptosis, and pain are common presenting symptoms. Treatmentfor orbital tumors involves radiation, which often causes opticneuropathies.

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15Abnormalities ofOptic Nerve Head

Reena M Choudhry, Saurabh Choudhry, Amar Agarwal

OPTIC ATROPHY

Optic atrophy is characterized by loss of conducting function of theoptic nerve, with an increase in pallor of the disk as a result of gliosisand loss of capillaries of the disk.1-16 Optic atrophy results from injuryto any portion of the retino-geniculate pathway (from retinal ganglioncells to lateral geniculate body).• Primary optic atrophy is caused by lesions which cause a death of

the axons of the optic nerve without causing a swelling of theoptic nerve. The lesions may affect the visual pathway fromretrolaminar portion of the optic nerve to the lateral geniculatebody. Causes of primary optic atrophy can be retrobulbar neuritis,compression due to aneurysms or tumors, toxic and nutritionalneuropathies and trauma.

• Secondary optic atrophy is caused by conditions, which produceswelling of the optic nerve head. The causes include papilledema,papillitis, and anterior ischemic optic neuropathy.

• Consecutive optic atrophy is a result of retinal or choroidal diseaseleading to destruction of ganglion cells. It could occur followingchorioretintis, Retinitis pigmentosa, pathological myopia, centralretinal artery occlusion and after pan retinal photocoagulation.

• Cavernous (Glaucomatous) optic atrophy is caused by loss of nervefibers in advanced glaucoma. The neuroretinal rim is healthy inglaucomatous optic atrophy in contrast to primary optic atrophywith a large cup.

• Segmental optic atrophy is usually seen in toxic and nutritionalneuropathies and ischemic optic neuropathies.

• Hereditary optic atrophy may be congenital or associated withLeber’s optic neuropathy, Kejr syndrome, Behr syndrome and othersystemic syndromes like Friedreich’s ataxia.


Clinical Features

• Primary optic atrophy shows chalky white disk (Fig. 15.1) withsharply defined margins and normal appearing retinal vessels andsurrounding retina (Table 15.1).

• Secondary optic atrophy shows dirty gray pallor of the optic nervehead with poorly defined margins, obliterated cup, sheathing andnarrowing of arteries in the peripapillary area.

• Consecutive optic atrophy shows waxy pallor of the disk withmarked attenuation of the arteries. Signs of associated retinalpathology are present.

• Cavernous optic atrophy shows a pale disk with pathologicalcupping, thinning of the neuroretinal rim, nerve fiber layer lossand laminar dot sign.

• Segmental optic atrophy shows pallor of the temporal side or othersegments with sharply defined margins and no retinal pathology.

• Relative afferent pupillary defect is present in unilateral andasymmetric cases.

• Color vision is reduced in correlation with the visual loss.• Visual fields show varied defects depending upon the cause of the

optic atrophy.• Kejr syndrome: This is an hereditary optic atrophy which is bilateral

and is autosomal dominant. It occurs between the ages of 4-10years.

• Behr syndrome: This is autosomal recessive and is another hereditaryoptic atrophy condition. Occurring during the first 10 years of life.

• Wolfram syndrome: This is another hereditary optic atrophy diseaseand is also referred to as DIDMOAD = Diabetes Insipidus, DiabetesMellitus, Optic Atrophy and Deafness.

Fig. 15.1: Optic atrophy

Abnormalities of Optic Nerve Head 187

Table 15.1: Differences between primary, secondaryand consecutive optic atrophy

Features Primary Secondary Consecutive

1. Disk color Chalky white Dirty grey Waxy pallor2. Margins Well-defined Blurred Well-defined3. Lamina Well-seen Not seen Well-seen

cribrosa4. Retinal Normal Peripapillary Marked

vessels sheathing and attenuationnarrowing of of arteriesarteries.Veins areTortous andWalls areSclerosed

5. Surrounding Normal Edema Associatedretina retinal

pathology6. Example Pituitary Papilledema, Retinitis

Tumor, optic papillitis pigmentosa,Nerve tumor CRA occlusion

• Foster-Kennedy syndrome: There is unilateral papilledema andcontralateral optic atrophy. It occurs due to frontal lobe tumors.

• Pseudo Foster-Kennedy syndrome: In this there is optic atrophy in oneeye and a disk swelling in the other eye due to AION.

Differential Diagnosis

One should differentiate between primary, secondary and consecutiveoptic atrophy (Table 15.1).

Optic Neuritis

Optic neuritis is defined as an inflammatory or demyelinating disorderof the optic nerve characterized by sudden loss or diminision of vision,associated with ocular pain and dyschromatopsia.1-16 Most commoncause of optic neuritis is demyelinating disorders like multiple sclerosis.Viral (mumps, measles, herpes zoster, cytomegalovirus, or HIV),bacterial (tuberculosis, syphilis or lymes disease) and other(histoplasmosis,cryptococcosis,toxoplasmosis or toxocariasis)infections can also cause optic neuritis. In children optic neuritis canoccur post-immunization. Other possible causes are adjacent paranasalsinus inflammation, systemic collagen vascular diseases and intraocular inflammation.


Clinical Features

• Decreased visual acuity ranging from 6/9 to no perception of light.There is rapid worsening in next few days reaching maximumdeficit by 1-2 weeks. Recovery occurs over next 4-6 weeks.

• Decreased color vision, which is more than the visual deficit.Acquired optic nerve disease tends to cause red-green defects. Anexception occurs in glaucoma and in autosomal dominantneuropathy which initially causes blue-yellow deficit. It has beenrecently found that visual field loss in glaucoma is detected earlierif perimetry is performed using a blue light stimulus on a yellowbackground. Acquired retinal disease tends to cause blue-yellowdefects except in cone dystrophy and Stargardt’s disease whichcause a predominantly red-green defect.

• Contrast sensitivity and stereoacuity is reduced.• Relative afferent pupillary defect (RAPD) is present in unilateral

or asymmetric cases.• Visual fields show central, centrocaecal or arcuate field defects.• Cells may be seen in the vitreous.• Fundus examination:

Retrobulbar neuritis: Optic disk appears normal (most commonpresentation in adults).

Papilitis: The disc appears swollen and hyperemic (Fig. 15.2A),associated with or without peripapillary flame shaped hemorrhages.Cells in the posterior vitreous may be present. Retina can show venoussheathing in the peripapillary area.

Neuroretinitis: Disk edema associated with macular star (leastcommon).

On fluorescein angiography (Fig. 15.2B) there is pre-papillarycapillary dilatation and leakage very similar to papilledema. There ishyperfluorescence of the disk with late leakage possibly involvingthe nerve fiber layer. With resolution of the swelling there is a paledisk with variable loss of the pre-papillary capillaries evidenced onfluorescein angiogram.

There is ocular pain, which worsens on ocular movements. Age atpresentation ranges between 20-45 years and women are morecommonly affected than men. In children the involvement is bilateral.Some patients may complain of defective color vision. Patients withmultiple sclerosis may have transient obscurations of vision on exertionor rise in body temperature (Uhthoff’s symptom).


Figs 15.2A and B: Papillitis: (A) color picture (B) FFA

Management

• In mild cases (vision 20/30 or better) only observation is indicated,as the disease is self-limiting.

• In cases where vision is 20/40 or worse intravenous (IV)methylprednisolone 1 gm daily for 3 days followed by oral steroids1 mg/kg body weight for 11 days is administered.

Optic Neuritis Treatment Trial (ONTT)

• Patients treated with intravenous methylprednisolone followedby oral steroids recovered vision faster than patients treated withoral steroids alone.

• The final visual outcome at 1 year was same with or without IVsteroids.

• Patients treated with oral steroids alone had higher rate ofrecurrences and increased rate of second eye involvement.


PAPILLEDEMA

Papilledema (Fig. 15.3) is a passive, non-inflammatory, hydrostaticedema of the optic nerve head, secondary to raised intracranialpressure (ICP).1-16 It is usually bilateral, although it may beasymmetrical. One should differentiate it from papillitis (Table 15.2).The following are the causes of raised ICP, which in turn causepapilledema.1. Intracranial space occupying lesions.2. Focal or diffuse cerebral edema.3. Blockage of flow of cerebrospinal fluid (CSF) within the ventricular

system (aqueduct stenosis).4. Reduced absorption of CSF (meningitis, subarachnoid hemorrhage,

etc).5. Hypersecretion of CSF by choroid plexus tumor.6. Increase in CSF viscosity (Guillain-Barre syndrome).7. Benign intracranial hypertension (pseudotumor cerebri).

Clinical Features

Clinically, papilledema can be classified into four stages.1. Early stage: In this stage the visual symptoms are absent and visual

acuity remains normal. Ophthalmoscopically the optic nerve headshows hyperemia, blurring of disk margins. Mild disk swellingmay be present which is best appreciated with slit lampbiomicroscopy. Absence of spontaneous venous pulsations couldbe an early sign of papilledema. Presence of spontaneous venouspulsations rules out papilledema.

Fig. 15.3: Papilledema


2. Established stage: In this stage patient may be asymptomatic orcomplain of transient visual obscuration lasting few seconds. Duringthese episodes the vision may vary from mild blurring to completeblindness. Ophthalmoscopically there is gross elevation of opticnerve head with engorged veins. The disk margins are markedlyblurred and edematous nerve fiber layer obscures the traversingblood vessels. Peripapillary splinter hemorrhages, cotton woolspots, choroidal folds and retinal striae (Paton’s lines) are present.The macula may have hard exudates forming an incomplete star.

3. Chronic stage: Constriction of peripheral fields may be associatedwith the enlargement of the blind spot. Ophthalmoscopicallyhemorrhages and disk edema slowly resolves. The cup ultimatelyobliterates and nerve fiber layer begins to atrophy giving graywhite color to the disk.

4. Atrophic stage; Secondary optic atrophy ensues. The optic disk ispale to white with indistinct margins and attenuated and sheathedvessels in the peripapillary area. Severe atrophy of nerve fiberlayer is present.

Other signs are:• The pupillary reactions are normal.• The color vision is unaffected in early stages but as the chronic

papilledema progresses to optic atrophy the color vision becomesabnormal.

• Visual fields—In the initial stages enlargement of the blind spot ispresent but as the atrophy sets in constrictions of peripheral fieldsare seen.

• Unilateral or bilateral sixth nerve palsy may be present due tostretching of the sixth nerve in the posterior fossa as a result ofraised ICP.

Table 15.2: Differences between papillitis and papilledema

Features Papillitis Papilledema

1. Laterality Unilateral Bilateral2. Onset Sudden Insidious3. Loss of vision Sudden Gradual4. Swelling of the disk Moderate Marked5. Field defects Central or Concentric

centrocaecal Contractionscotoma of the visual

field6. Posterior vitreous Fine opacities Clear


Very rarely papilledema may be unilateral or more pronounced inone eye than the other (preexisting unilateral optic atrophy, FosterKennedy syndrome or unilateral congenital anomaly of optic nervesheath) (Fig. 15.4).

On the fluorescein angiogram there is immediate filling of thedilated capillaries giving hyperfluorescence and leakage from boththe prepapillary and peripapillary capillary plexus and associatedleakage into the surrounding retina.

With resolution of the papilledema the optic disk is flat and paleand there is lack of filling of the pre-papillary capillary plexus. Inlong-standing cases, the prepapillary capillary plexus mightanastomose with the choroidal plexus with a consequent optociliaryshunt vessel. In chronic papilledema the optic disk becomes pale andthere is only minimal leakage of fluorescein.

Ocular symptoms mainly consist of bilateral transient obscurationsof vision lasting few seconds. These are often precipitated by posturalchange. Rarely patients may complain of reduced vision. Doublevision, which may be intermittent, can be present in some cases.Systemic symptoms are associated with raised ICP and consist ofheadaches, which are more severe early in the morning or in therecumbent position. Other symptoms like nausea, vomiting, loss ofconsciousness and motor rigidity may be present.

Fig. 15.4: Foster-Kennedy syndrome


Management

The treatment is focused towards the cause of raised ICP. If increasedICP is related to a mass lesion, removal of the mass is the obvioustreatment of choice. Medical treatment in the form of carbonicanhydrase inhibitors may help reduce the ICP. If the lesion cannotbe removed, or if the CSF absorption is reduced then treatment isdirected towards shunting of the CSF into the peritoneal cavity(Lumboperitoneal shunts). In cases of idiopathic intracranialhypertension optic nerve sheath decompression has been advocatedby some authors to alleviate fluid retention within the surroundingmeninges by creating a small fenestration site within the intraorbitalportion of the nerve. While this procedure has yielded some positiveresults, it is extremely complex work and may fail in up to one-thirdof all cases.

ARTERITIC ANTERIOR ISCHEMIC OPTIC NEUROPATHY (AAION)

Etiology

AAION is infarction of the prelaminar or laminar portion of opticnerve head due to inadequate perfusion by posterior cilliary arteriesand is most commonly associated with giant cell arteritis (GCA). GCAis the most common cause of AAION. Other conditions that may causeAAION are herpes zoster, rheumatoid arthritis, relapsingpolychondritis, Takayasu’s arteritis, systemic lupus erythematosus,and periarteritis nodosa.

Classic Signs

• Unilateral visual loss (gross reduction of vision).• Relative afferent pupilliary defect (RAPD) is present in unilateral

cases.• Fundus examination shows pale and swollen disk. Splinter

hemorrhages at and around the disk margins may be present.Within 1-2 months the disk swelling subsides and optic atrophyensues.

• Visual fields commonly have altitudinal defect in eyes which canbe tested.

• In few cases cranial nerve palsy may be present as an associatedsign.

• Systemic signs of GCA are tender, palpable non-pulsatile temporalarteries.


• Involvement of other arteries may lead to myocardial infarction,renal failure and brainstem stroke. In some cases central retinalartery occlusion may be an associated finding.

• Erythrocyte sedimentation rate (ESR) and C-reactive protein areinvariably raised.

Symptoms

Patients classically present with sudden onset unilateral visual loss(partial or complete), which may rapidly become bilateral. Averageage of presentation is usually 55 years and above. Women are affectedmore commonly than men. Patients may give history of amaurosisfugax before the onset of visual loss. Diplopia may be present in fewcases. Systemic complaints of headaches, jaw claudication, scalptenderness, myalgia, fever and weight loss may be present.


1. Non-arteritic anterior ischemic optic neuropathy- Patients are younger than those with GCA.- The visual loss is less severe.- Systemic hypertension or diabetes mellitus is frequently present.- Erythrocyte sedimentation rate (ESR) is usually normal.- Involvement of other eye is less common.- No benefit from systemic steroids.

2. Optic neuritis (papillitis)- Affects younger age group (20-40 years).- The visual loss is severe and recovery is better.- Pain during ocular movements is frequently present.- The disk swelling is hyperemic and associated with cells in

posterior vitreous.3. Compressive optic neuropathy

- Visual loss is gradual in onset and slowly progressive.- Disk edema may be absent.- Proptosis or restricted ocular movements are often present

(associated with orbital disease).- Systemic signs and symptoms of GCA are absent.

Work-up

1. Temporal artery biopsy should be performed in patients whereGCA is suspected before starting steroid therapy or within 2 weeks.(The biopsy specimen should be at least 2.5 cm long and if the


biopsy is negative but response to steroids is positive biopsy ofopposite artery should be considered).

2. Temporal artery Doppler can also be done.

Risk Factors

In AAION associated with GCA the involvement of other eye withouttreatment is seen in 50 percent of cases within days to few weeks.

Management

AAION is a medical emergency and needs to be treated with intravenous methyl prednisolone 1 gm daily for 3 days followed by 80-100 mg oral corticosteroids on a slow tapering dose for a period of 6months to 1 year to prevent involvement of the other eye. Patients ofGCA confirmed by temporal artery biopsy are maintained on initialdose of corticosteroids for 4 weeks until ESR normalizes and slowlytapered while monitoring the ESR levels.

Pharmacology

Rare instances of anaphylactoid (e.g., bronchospasm) reactions haveoccurred in patients receiving parenteral corticosteroid therapy soappropriate precautionary measures should be taken prior toadministration, especially when the patient has a history of allergy toany drug. There are also reports of cardiac arrhythmias and/orcirculatory collapse and/or cardiac arrest following the rapidadministration of large IV doses of methylprednisolone sodiumsuccinate (greater than 0.5 gram administered over a period of lessthan 10 minutes). Bradycardia has been reported during or after theadministration of large doses of methylprednisolone sodium succinate,and may be unrelated to the speed or duration of infusion.

POSTERIOR ISCHEMIC OPTIC NEUROPATHY (PION)

In the posterior variety (PION) there is no disk edema noted in theacute phase although the symptoms and clinical findings are otherwisesimilar to the anterior variety. The circulation impairment affects theposterior vessels and there is no impairment of the axoplasmic flow .

The PION is seen more frequently in cases with acute severe bloodloss or sustained hypotension, postsurgical complications, migraine,collagen vascular diseases and giant cell arteritis.


REFERENCES

1. Hayreh SS. Risk factors in AION. Ophthalmology. 2001;108(10):1717-8.2. Chan CC, Paine M, O’Day J. Steroid management in giant cell arteritis. Br J

Ophthalmol. 2001;85(9):1061-4.3. Ischemic Optic Neuropathy Decompression Trial: twenty four month update.

Arch Ophtalmol. 2000;118(6):793-8.4. Beri M et al. Anterior ischemic optic neuropathy. VII. Incidence of bilaterality

and various influencing factors. Ophthalmology. 1997;94(8):1020-8.5. Jacobs M, Taylor D. The systemic and genetic significance of congenital optic

disc anomalies. Eye. 1991;5(Pt4):470-5. Review.6. Villalonga Gornes PA, Galan Terraza A, Gil-Gibernau JJ. Ophthalmoscopic

evolution of papilary colobomatous malformations. J Pediatr OphthalmolStrabismus 1995;32(1):20-5.

7. Frisen L, Holmegaard L. Spectrum of optic nerve hypoplasia. Br J Ophthalmol.1978; 62(10:7-15).

8. Traboulsi EI, O’Neill JF. The spectrum in the morphology of so called “morninggllory disc anomaly”. J Pediatr Ophthalmol Stabismus. 1998;25(2):93-8.

9. Lee MS, Gonzalez C. Unilateral peripapillary myelinated retinal nerve fibersassociated with stabismus, amblyopia, and myopia. Am J Ophthalmol.1998;125(4):554-6.

10. Principles and Practice of Ophthalmology by Albert Jackobiec, Chapter 20;Page:2549-60.

11. Atlas of optic neuritis disorders by Thomas J Spur.12. Focal points 1993, Module 5, Henry JL Van, DyK.13. Walsh and Hoyt’s Clinical Neuro-opthalmology. 5th Edition. The Essentials.

Neil R Miller, Nancy J Newman. 196-220.14. Trobe JD, et al. The impact of optic neuritis treatment trial on the practices of

ophthalmologists and neurologists. Ophthalmology. 1999;106(11):2047-53.15. Agarwal, et al. Textbook of Ophthalmology 4th vol.; Jaypee; India; 2003.16. Amar Agarwal. Handbook of Ophthalmology; Slack inc, USA, 2006.

16 Ocular Myopathies

S Soundari

INTRODUCTION

Myasthenia results from the dysfunction of the neuromuscular junctioncaused by autoimmunity. Ocular myasthenia most commonly presentswith diplopia, ptosis or both that is variable and characteristicallyworse towards the end of the day. Serum antibodies to acetylcholinereceptors are detected in 90 percent of the patients with generalizedmyasthenia but only 50 percent will be detected in ocular myasthenia.Neonatal forms of myasthenia gravis occur in 10 to 15 percent ofchildren born to the mothers with myasthenia gravis, because of theplacental transfer of antibodies to ach receptor.

The impairment of the neuromuscular conduction causes weaknessand fatigue of the skeletal musculature, but not of cardiac andinvoluntary muscles. The disease affects females twice as commonlyas males and may be ocular, bulbar or generalized.

CLINICAL FEATURES

• Myasthenic signs and symptoms are variable and tend to worsewith fatigue and stress

• Fatigability: When testing for lid fatigue, the patient is asked tolook up without blinking at the examiners hand for 1-2 min. Lidfatigue on prolonged up gaze is perhaps the most frequently elicitedsigns

• Peek sign: When the patient is asked to close the lids gently, one orboth inadvertently open slightly or peek

• There can absence of Bell’s phenomenon• Cogan’s lid twitch: After prolonged down gaze refixation to the

primary position results in overshooting of the upperlid• Hop of the upper lid occurs on looking to the side


• Myasthenic ptosis, when unilateral is associated with controlaterallid retraction

• If one eye lid is elevated manually as the patient looks up, thefellow eyelid will show fine oscillatory movements

• Ice pack test: The degree of ptosis improves after the ice pack isplaced on the eyelid for 2 minutes. The test is negative in nonmyasthenic ptosis

• Diplopia: This is very frequently vertical although any of the musclecan be involved. Pupil is not involved. A pseudointernuclearophthalmoplegia can occur

• Saccadic abnormalities like hypometric large saccades, hypermetricsmall saccades, quiver movements, hyper fast saccades can occur.

Investigations

Tensilon test: Intravenous injection of edrophonium is the gold standardfor the diagnosis of ocular myasthenia. Edrophonium is a short actinganticholinestrase which increases the amount of acetylcholine availableat the neuromuscular junction. In myasthenia this results in transientimprovement of symptoms and signs such as weakness, ptosis anddiplopia. Uncommon complications include bradycardia, loss ofconsciousness and even death. Lacrimation, salivation and abdominalcramps are mentioned as common minor side effects. The test shouldbe done with a resuscitation trolley in hand if in case of suddencardiorespiratory arrest.

Objective baseline measurement of ptosis or diplopia with hesschart should be taken. Intravenous injection of atropine 0.3 mg isgiven to minimize muscarinic side effects. Intravenous dose of 0.2 ml

Fig. 16.1: Myasthenia

Ocular Myopathies 199

containing 2 mg of edrophonium hydrochloride is given, if definitiveimprovement is noted the test can be terminated.

If no response then the remaining 0.8 ml of 8 mg is injected after60 seconds if there is no adverse reaction. The response lasts only for5 minutes.

Perverse reaction like worsening of the strabismus or a paradoxicalresponse like right hypertropia becoming a left hypertropia after theinjection is considered positive by some.

Neostigmine Test

• Intramuscular injection of neostigmine is useful in children. Theeffect lasts for 15 minutes to peak and lasts for only 30 minutes

• Presence of acetylcholine receptor antibodies is virtually diagnosticof myasthenia gravis.

Electromyography

• Repetitive stimulation and single muscle fiber will show adecremented response

• Sleep test is useful in neonates and babies. There will beimprovement after sleep

• Imaging the chest with the computed tomography or magneticresonance imaging for the presence of thymoma.

Differential diagnosis for myasthenia gravis:• Isolated or combined third, fourth, sixth or seventh cranial nerve

palsies• Decompensated strabismus• Thyroid disease• Eaton lambert myasthenic syndrome• Botulism• Chronic progressive ophthalmoplegia• Myotonic dystrophy.

Treatment

Treatment of myasthenia gravis can be divided into—opticaltreatment, medical, and surgical treatment.

Optical Treatment

• Because of the variability of signs and symptoms it is difficult totreat. For binocular diplopia occlusion of one eye, but it makes thepatient to view monocularly


• Fresnel prism can be tried if the ocular deviation is stable for weeks• The crutch glasses are helpful in the case of ptosis.

Medical Treatment

• Anticholinergic drugs like pyridostigmine (60 mg) three times aday. One must be always aware of the cholinergic crisis if toomuch of pyridostigmine is given. The patient should be told tostop if bulbar symptoms or generalized weakness occurs.

• Corticosteoids is used along with pyridostigmine. The patientshould be maintained on steroids for months before tapering andshould be a slow tapering for months when the patient ismaintained on low dose of steroids there can relapse or unmaskingof generalized myasthenia.

• Immunosuppressant: Azathriopine is effective against myasthenia.It is given in the dose of 2-3 mg/kg/day

• Cyclosporine A, plasmapheresis, mycophenolate and IV gammaglobulin also can be used in generalized myasthenia.

Surgical Treatment

• Thymectomy is very effective for ocular myasthenia. The result ofthymectomy for generalized myasthenia are very favorable withabout 35 percent entering complete remission and 50 percentimproving.

• Eyelid surgery or ptosis and eye muscle surgery for diplopia areconsidered only if it is stable for few months and as a last resort.

CHRONIC PROGRESSIVE EXTERNAL OPHTHALMOPLEGIA

The clinical features are the involvement of the upgaze and then thelateral movements and may later be affected in all gaze resulting in afixed globe. Because the muscle involvement is symmetrical, diplopiadoes not usually occur. There is also slowly progressive bilateral ptosis.

Kearns-Sayre Syndrome

• This is a mitochondrial cytopathy, inherited from the mother.• It is characterized by pigmentary retinopathy with coarse

granularity.• Conduction defects of the heart can occur. Heart block may result

in sudden death.• Other features are short stature, muscle weakness, cerebellar ataxia,

neurosensory deafness, mental handicap and delayed puberty.


Treatment

Treat the associated conditions. Lubricants for the exposurekeratopathy, base down prisms within reading glasses for reading ifthe down gaze is restricted.pacemaker may be required for the cardiaccondition. In ocular pharyngeal dystrophy, for the dysphagia andaspiration cricopharyngeal surgery. Genetic counseling.

MYOTONIC DYSTROPHY

This is dominantly inherited in the gene of chromosome 19q.Usually manifest in the third decade. Peripheral muscle

involvement which makes the release of grip difficult which can betested with the Hand Shake. A mournful expression caused by bilateralfacial muscle wasting. Slurred speech because of the involvement oftongue muscles and pharyngeal muscles hypogonadism, frontalbaldness, intellectual detoriation, pulmonary and cardia complicationcan occur.

Other ocular features are presenile cataract with polychromaticluster, ptosis, pigmentary retinopathy, light near dissociation, externalophthalmoplegia.

ESSENTIAL BLEPHAROSPASM

Blepharospasm can be a very disabling condition in terms of visionand social life.

More commonly affects female in the older age group. This is atype of facial dystonia in which there idiopathic tonic contraction oforbicularis oculi. If it is secondary to any ocular pathology (corneal orconjuctival foreign body, trichiasis, blepharitis, dry eyes) then it iscalled secondary blepharospasm.

Clinical Features

• There is a bilateral involuntary lid closure which may beprecipitated by stress, fatigue, social interactions. This is alwaysbilateral. Disappears during sleep

• Secondary ocular changes like ptosis or entropion can occur• This can be differentiated from hemifacial spasm which does not

disappear during sleep.

Treatment: Botulinum toxin given as multiple injections on the upperand lower lid. The effect generally last for 3 months time. In cases ofsecondary blepharospasm treat the underlying cause which isprecipitating the blepharospasm.


Other treatment option are medical like benzodiazepine or surgicallike myectomy.

Meige’s SyndromeThis is a blepharospasm with midfacial spasm. It may lead on tocompromise of speech , eating and drinking.

Breughel SyndromeThis is associated with severe mandibular and cervical muscleinvolvement.

Hemifacial spasm:This is a tonic clonic spasm of the musculature which occurs evenduring sleep. Usually affects the younger age group. It is thought tobe caused by the irritation of the root of seventh cranial nerve by acompressive lesion. MRI of the cerebellopontine angle should beobtained to rule out tumor.

Treatment

It includes observation, botulinum toxin injection or neurosurgicaldecompression of the seventh nerve (Janetta procedure)

Tourette’s Syndrome

This includes multiple compulsive muscle spasms associated withutterances of bizarre sounds.

Fig. 16.2: Blepharospasm


Tic Douloureux

Acute episodes of pain in the areas of distribution of the trigeminalnerve.

Tardive Dyskinesia

This is a orofacial dyskinesia, often with restlessness and dystonicmovements of the trunk and the limbs. Ususlly it is associated withthe long-term use of antipsychotic medication.

Facial Myokymia

Fleeting movements of the facial musculature which may be associatedwith stress, multiple sclerosis, caffeine or rarely tumors of the brainstem.

Lid Apraxia

• In lid opening apraxia there is total inhibition of the LPS with noactivation of orbicularis oculi. This results in the lid closure withdifficulty in initiating the lid opening. It is associated withparkinson’s disease, progressive supranuclear palsy, Huntington’sdisease and Wilson’s disease.

• Lid retraction and poor closure of the lids can occur in Parkinson’s,Parinaud’s and progressive supranuclear palsy.

BIBLIOGRAPHY

1. Amar Agarwal. Handbook of Ophthalmology; Slack USA 2005.2. American Academy of Ophthalmology- section 5- Neuro-ophthal 2004-2005.3. Jack J Kanski (6th ed) Clinical ophthalmology, Butterworth Heinmann 2007.4. Parson’s Diseases of The Eye (18th ed) Butterworth-Heinemann International

editions.5. Sunita Agarwal, Athiya Agarwal, et al. Textbook of Ophthalmology 4th vol.;

Jaypee, India 2003.

17 Miscellaneous

Jeyalakshmi Govindan, S Soundari

PITUITARY TUMORS

INTRODUCTION

Pituitary adenomas occur most frequently between the fourth andsixth decade of life. Pituitary adenomas with secretory function canclinically manifest endocrine acivity. It can be either eosinophilic orbasophilic.

Eosinophilic adenomas secretes excessive amount of growthhormone producing acromegaly in adults and gigantism in the young.The hands and feet are enlarged, the jaws become prominent, thetongue is thickened, and the libido fails. Amenorrhea in the femaleand impotence in the male develop.

Prolactin secreting adenomas results in galactorrhea andamenorrhea.

Basophilic adenomas secrete ACTH and produce cushing’ssyndrome. The clinical features of basophilic adenoma includeadiposity, moon face, hypertension, hypogonadism and osteoporosis.

Visual failure and field defects are less common with functionaladenomas than with nonfunctional adenomas.

Nonsecreting chromophobe adenoma is a highly commonintracranial tumor. Pituitary hypofunction may be present in somecases.

Headache is the most common neurological manifestation. Burstingheadache is considered as the characteristic of pituitary adenoma.

Loss of vision is the predominant ocular manifestation. The greatmajority of the visual symptoms consisted of visual loss in one orboth eyes. The visual loss preceded other symptoms and signs suchas headache and endocrinopathy in many patients.

Miscellaneous 205

The location of the chiasma may be:Central chiasma: Chiasma lies directly above the sella , normally 80

percent of the individuals have central chiasma.Post fixed: Chiasma is located more posteriorly on the dorsum

sella,present in 10 percent of the individuals. If there is a involvementfrom pituitary tumors the optic nerves are involved first.

Prefixed: Chiasma located anteriorly over the tuberculum sella. Ifthere is an involvement from the pituitary tumors the tract fibers getinvolved first. Present in 10 percent of the normals.

If the chiasma is central both superotemporal fields are initiallyaffected as inferonasal fibers pass low and anteriorly. As the tumorgrows the inferior temporal field defect progress.

The patient may not present until the central field is involved.Color desaturation across the midline is the earliest sign of chiasmal

field defect.Optic atrophy is present in 50 percent of the patients.The other features which the patient can present with, is the seesaw

nystagmus of Maddox and diplopia as a result of involvement of thecavernous sign and involvement of cranial nerve.

Investigation

• Coronal plane MRI is the investigation of choice• Endocrinological evaluation according to the clinical presentation.

Treatment

• Surgery for the pituitary tumor through transsphenoidal approach• Bromocriptine can shrink prolactinomas• Radiotherapy can also be used.

CRANIOPHARYNGIOMA

It is a slow growing tumor of Rathke’s pouch. It can interfere withthe hypothalamic function resulting in dwarfism, delayed sexualdevelopment and obesity.

As the tumor compresses from above and behind the infero-temporal field defects starts early as the upper nasal fibers pass highand posteriorly.

MRI shows the location of the tumor.CT scan shows calcification in 60 percent of the cases.Treatment is mainly surgical. Postoperative radiotherapy may be

helpful but recurrence are common.


HEADACHE

INTRODUCTION

Headache is defined as pain in the head that is located above the eyesor the ears, behind the head (occipital), or in the back of the upperneck. Headache is a universal experience as over 90 percent ofindividuals have noted at least one headache during their lifetime.

History

The cause can usually be elicited from the history. Points to be notedare mode of onset, duration, frequency, location, nature of headache,prodromal symptoms, precipitating relieving factors and medicalhistory and medication list.

Omnious signs of headache include:1. Abrupt onset, after 4th decade2. Progressive symptoms3. Focal neurological signs4. Associated with fever, cough, straining5. Change with position or exertion.

Classification

There are two types of headaches: Primary headaches and secondaryheadaches. Primary headaches are not associated with (caused by)other diseases. Examples of primary headaches are migraineheadaches, tension headaches, and cluster headaches. Secondaryheadaches are caused by associated disease. The associated diseasemay be minor or serious and life threatening.

Migraine

A migraine is a common type of headache that may occur withsymptoms such as nausea, vomiting, or sensitivity to light. In manypeople, a throbbing pain is felt only on one side of the head.

An estimated 18 percent of women and 6 percent of men experiencerecurrent headache classified as migraine. It tends to start from age10 but the peak prevalence is between the ages of 25 and 55.70 to 90percent of migraine patients have a positive family history. Evidencesuggests involvement of genetic factors in that defective gene encodesfor a voltage dependent calcium channel that ultimately leads toneuronal excitability.

Miscellaneous 207

Pathophysiology of migraine is not clearly understood. Evidencesuggests the role of trigeminal –vascular projections and theneurochemical serotonin. The hyperexcitability of brain stem neuronsis caused by release of vasoactive neuropeptides which also stimulateinflammatory cascade dilating meningeal vessels(pain) and activatingportions of cortex(aura).

Variour trigger factors that are thought to bring about migraineinclude certain foods, especially chocolate, cheese, nuts, alcohol, stress,sleep deprivation or birth control pills.

Symptoms and Signs

The headache usually begins in the fronto temporal region, unilateralbut can be bilateral. The onset is usually gradual. The episodes maystart after awakening and are generally relieved by sleep. The auraof headache precedes by 15-45 minutes. It may include• Scotoma (blind spots)• Fortification (zig-zag patterns)• Scintilla (flashing lights)• Unilateral paresthesia/weakness• Hallucinations• Hemianopia

Classification of Migraine Based on Clinical Presentation

1. Common migraine (80%) - Preceded by nausea, vomiting(headache without aura) and autonomic symptoms

2. Classic migraine (20%) - Preceded by visual or sensory(headache with aura) dysfunction

3. Acephalic migraine - Transient neurological eventswithout headache occur overthe age of 40.

4. Complicated migraine - Migraine with permanentneurological deficit.

5. Ophthalmoplegic migraine - Ipsilateral palsy of one or moreextraocular muscles as themigranous headache is resolving.Common before the age 10.

6. Retinal migraine - Sudden monocular visual losswithout flashes.Occasionally constriction ofretinal arterioles and venulesnoted.


7. Basilar migraine - Bilateral blurring of vision,field defects, ataxia vertigo,nystagmus, dysarthria

INTERNATIONAL HEADACHE SOCIETY

Criteria for Migraine Without Aura

A. Five attacks fulfilling criteriaB-DB. Headache lasting for 4 to 72 hours(untreated)C. Headache has two of the following:

1. Unilateral2. Pulsating quality3. Moderate to severe intensity4. Aggravated by physical activity.

D. During headache at least one of the following:1. Nausea or vomiting2. Photophobia or phonophobia.

Diagnosis

Neuroimaging is rarely indicated in a patient with typical migraineand a normal examination. CT scan of the head is indicated to ruleout intracranial mass or hemorrhage in selected or atypical cases. MRIand magnetic resonance angiography are more sensitive. They areuseful if neurologic examination findings are abnormal, the migraineoccurs for the first time after age 40 years, the frequency or intensityis increasing, and the accompanying symptoms of the attack change.Lumbar puncture is done when suspecting a diagnosis of subarchnoidhemorrhage, meningitis or pseudotumor cerebri.

Treatment

Symptomatic or abortive therapy is helpful when the attack occursless than twice a week and short lived (Table 17.1). Prophylactictherapy (Table 17.2) is indicated when the headaches are more frequentor produce significant disability.Elimination of triggering factorscontributes to prevention.

Miscellaneous 209

Tension Headache

It is the most common type of chronic recurring pain. Tension headachecan be episodic or chronic. The pain is often described as pressure ortightness. It may occur under emotional stress or intense worry.Tenderness may be elicited in the scalp or neck.

Criteria for Episodic Tension Headache

A. At least 10 previous headache episodes for filling criteria B-D.B. Headache lasting for 30 minutes to 7 days.C. At least two of the following:

1. Pressure/tightening quality2. Mild or moderate intensity3. Bilateral location4. No aggravation with physical activity.

D. Both of the following:1. No nausea or vomiting2. Photophobia and phonophobia are absent.

Treatment

The abortive and prophylactic medications for migraine may be tried.The antidepressants nortryptiline and amitryptiline may be the firstline agents for these patients. Botox injected into the frontal andoccipital muscles has been tried in refractory tension headache.

Table 17.1: Abortive Therapy in Migraine

Triptans - Sumatriptan, Rizatriptan, Zolmitritan, EletriptanNSAIDs - Naproxyn, Indomethacin, ketorolacAntiemetics - Droperidol, Prochlorperazine, MetoclopramideCorticosteroids - Prednisone, MethylprednisoloneMiscellaneous - Acetaminophen, caffeine, Ergotamine, Butalbital

Table 17.2: Preventive Therapy in Migraine

Beta blockers - Propranolol, NadololCalcium channel - Verapamil, NifedipineBlockersAntidepressants - Amitriptyline, FluoxetinAnticonvulsants - Valproic acid,TopiramateMiscellaneous - Lithium, Methysergide


Cluster Headache

Cluster headache, also known as histamine headache refers to agrouping of headaches, usually over a period of several weeks. Attacksusually are severe and unilateral and typically are located at the templeand periorbital region predominanatly occurs in middle agesmen.Alcohol is common trigger.About 30 to 50 percent of patientswill develop signs of Horner syndrome.

Criteria for Cluster Headache

A. At least five attacksB. Severe unilateral orbital,supraorbital or temporal pain lasting 15

to 180 minutesC. Headache associated with at least one of the following:

1. Conjunctival injection2. Lacrimation3. Nasal congestion4. Rhinorrhea5. Forehead and facial sweating6. Miosis7. Ptosis8. Eyelid edema

D. Frequency of attacks from one to eight per day.The major entity to exclude in a patient with painful horner

syndrome is carotid dissection.

Treatment

The following may be tried in acute cluster attack:• 100 percent oxygen via a facemask• Subcutaneous or intranasal sumatriptan• Intranasal dihydroergotamine• Corticosteroids.

Preventive therapies that are available are lithium, verapamil,methysergide.

Headache and Ocular Diseases

Headache due to ocular causes are often associated with periorbitalpain and other eye signs. Some of them are given in the table.

Miscellaneous 211

Ocular diseases Examples Clinical features

1. Corneal diseases Corneal erosions Severe pain and foreignbody sensation on awakening

2. Intraocular causes Scleritis, iritis, Angle Pain over the eye, tender toclosure glaucoma palpate and photophobia

is universal3. Optic nerve Optic neuritis pain on eye movements and

diseases eye may be tender4. Eye strain Uncorrected Hyperopic Pain over the brow,

Refractive error, spreading to scalpConvergence insufficiency

The Differential Diagnosis of Headache Disorders

Entity Characteristics of pain

Subarchnoid hemorrage Acute, occipital, worst ever, with meningismusBrain tumor Subacute dull ache with focal signsHypertension Acute frontal or occipital throbbingPseudotumor cerebri Subacute, dull, with transient visual loss

and papilledemaMeningitis Acute or chronic, throbbing, with fever

and meningismCarotid dissection Throbbing pain over periorbital, with horner’s

syndrome or ipsilateral visual lossTemporal arteritis Severe pain over the temple, tenderCough headache Cough induced headache may be associated

with posterior fossa lesionsHypnic headache Throbbing, global in location after falling asleep,

short lived in elderly

FUNCTIONAL VISUAL LOSS

INTRODUCTION

An apparent loss of visual acuity or visual field with no substantiatingphysical signs;often due to natural concern about visual loss combinedwith suggestibility and a fear of the worst; best treated withreassurance.

Functional visual loss (FVL) is frequently encountered inophthalmic practice. Identifying such patients is extremely importantin order to avoid unnecessary laboratory testing and secondary gain.


Clinical Presentation

• Binocular (rare) and monocular blindness• Decreased visual acuity (LP to 20/30) or fluctuating acuity on

different visit• Visual field defects - monocular hemianopias, bitemporal and

binasal defects, ring scotomas, tubular fields, spiral fields, star-shaped fields

• Diplopia• EOM paralysis• Paralysis, spasm and sluggish accommodation• Voluntary nystagmus• Total color blindness, non-recognition of Ishihara demo plate• Disturbances of reading and writing• Frequent blinking and blepharospasm• Ocular Munchausen’s syndrome

FVL also has been reported in children due to underlying lack ofparental attention or move to a different school.

Tests for Functional and Simulated Defects

The diagnosis can be made only with high degree of suspicion. Thetests must be objective in nature.• Attitude of the patient: A patient with true vision loss tends to

move cautiously, the hysterical patient move flawlessly; themalingerer will purposely bump into things.

• Visual acuity: This is one of the most important tests as visionloss is the most common symptom of FVL. Varying test distance isa useful technique.

• Pupillary reflexes: A patient who complains of total blindness withintact pupillary responses but no cortical lesion is likely to befunctional.

• Menace reflex: Blinking to visual threat• Stereopsis: Touching index fingers togther depends on

proprioception and not on vision.• Optokinetic nystagmus: One eye observed ophthalmoscopically,

while the drum revolves before the other. A slight nystagmus willbe easily observed.

• Head rotation nystagmus test: Head is rotated passively about30° alternatively to right and left. The presence of vestibularnystagmus indicates true blindness.

• VEP: The flash evoked visual potential can be used to documentintact visual pathway.

Miscellaneous 213

Tests for Simulation of Uniocular Blindness

• Fixation test: Relies on refixation movement. A four diopter baseout prism is placed infront of alleged blind eye. A true blind willshow no refixation movement.

• Diplopia test(Graefe’s test): The suspected eye is covered anduniocular diplopia elicited in the good eye by bisecting the pupilwith the use of a strong prism.The suspected eye is then quicklyuncovered and simultaneously the prism is slipped over the wholepupil of the other. If diplopia is still confessed malingering isproved.

• Fogging test: Add progressively strong concave or convex lens infront of good eye as the patient reads. If reading continues visionwith other eye is proved.

• Color tests: Vectographic or duochrome visual acuity testing arealso useful in patients with monocular complaints.

Tests for Simulated Abnormal Visual Field

• Monocular visual field defects: The most valuable instrument inthe detection of FVL is the tangent screen as test distance can bevaried. Patients with FVL typically manifest with tubular fields,i.e. the field remains the same size regardless of test distance.Also seen are spiraling and crossing isopters.

• Binocular field defects: Standard perimetry is performed withboth eyes open patient with FVL never realize the extent of nasalfield of the contralateral eye.But automated perimetry does notdefinitely distinguish an organic defect from a functional one.

• Central scotomas: It can be tested using the red Amsler’s grid andthe red/green glasses.If the scotoma disappears when the red lensis over the affected eye and the green lens is over the good eyethen the patient is functional.


• Amblyopia• Optic neuropathies• Retinal degeneration• Cortical visual loss.

When the diagnosis is uncertain MRI with contrast, ERG can beperformed. Rarely neuroimaging with positron emission tomographymay be done for suspected cortical visual loss.


Management

The successful management lies in physician’s empathy andencouragement. Emphasis must be laid on statements such as peripheralvision seems good and optic nerves are healthy.

Treatment such as prescription of drops, low power spectaclesand ‘retinal test’ where both eyes are patched and patient is isolatedtend to satisfy them and improve the FVL. Finally psychiatricconsultation is required in some patients.

In children with FVL the prognosis for visual recovery is excellent.

OCULAR MANIFESTATIONS OFINTRACRANIAL ANEURYSMS

INTRODUCTION

The ophthalmologist may be the first physician to encounter clinicalmanifestations of intracranial vascular abnormalities that may heralddevastating neurological complications. The common intracranialvascular abnormalities are intracranial aneurysms, carotid-cavernousfistulas and arteriovenous malformations.

Intracranial Aneurysms

An estimated 1 to 6 percent of the general population harbors anintracranial aneurysm. The annual rupture rate of aneurysms has beenestimated to range from 0.05 to 2 percent, with a higher rate associatedwith a previous history of subarachnoid hemorrhage (SAH),symptomatic clinical presentation (mass effect or cranial neuropathy),large aneurysm size (>10 mm) or posterior circulation location.

Subarachnoid Hemorrhage

It is the most common manifestation in 90 percent of cases. 10 to 20percent of patients presenting with aneurysmal subarachnoidhemorrhage (SAH) will die immediately prior to seeking medicalattention. Others may develop papilledema, subhyaloid hemorrhage(terson’s syndrome), and paresis of lateral rectus of both eyes.Complications after SAH are rerupture, hydrocephalus, and delayedcerebral arterial vasospasm with ischemic neurologic deficits.

Miscellaneous 215

Intracranial aneurysm can be congenital, saccular or berry aneurysmoccurring in association with circle of Willis. The ocular manifestationsdepend on mechanical pressure on the structures nearby, suddenincrease in size (>1 cm) and rupture.

The unruptured aneurysms of the internal carotid, anteriorcommunicating, posterior communicating and middle cerebral causemass effect. The symptoms can be retro-orbital pain, third cranialnerve palsy, cavernous sinus syndromes, hydrocephalus, visual fielddeficits (Table 17.3), mild to moderate hemiparesis, or hypothalamic-pituitary dysfunction.

Carotid cavernous aneurysms are uncommon accounting for only2 percent of all intracranial aneurysms. The aneurysm frequentlyinvolve the abducent nerve early. The pupil sparing third nerve palsyand ophthalmic(V1) involvement may also occur. The aneurysmalrupture result in carotid-cavernous fistula (see below) and rarely SAH.

Diagnosis

Transfemoral cerebral angiography is currently the “gold standard”for diagnosing intracranial aneurysms. An angiogram providesimportant information about site, size, direction of the aneurismaldome and neck, and relationship with the parent vessel andperforators. A transcranial Doppler study is useful in detecting thedevelopment of arterial vasospasm.

A CT scan is important for establishing the diagnosis of SAH. AnMRI scan is becoming an important tool for diagnosing a cerebralaneurysm. Currently, it will detect, with high reliability, aneurysmsthat are larger than 5 mm. This ability may be especially useful formonitoring a patient with a small, unruptured aneurysm. An MRIscan is also helpful in demonstrating the degree of intramuralthrombus in giant aneurysms. In fact, magnetic resonance angiographymay eventually replace transfemoral cerebral angiography.

Table 17.3: Visual field defects due to intracranial aneurysms

Aneurysms Visual field defects

Internal carotid artery Nasal hemianopia on the affected side andtemporal hemianopia on the other sidebitemporal hemianopia

Anterior and middle cerebral From above bitemporal hemianopiaPosteriorly homonymous hemianopia


Management

Surgical intervention is typically recommended for unrupturedaneurysms (same as CCF below).

Carotid-Cavernous Fistula

Carotid-cavernous fistulas (CCFs) are abnormal communicationsbetween the carotid arterial system and the venous cavernous sinus.

Mechanism of Direct CCF

• Trauma (75%): High flow basal skull fracture• Spontaneous causes (25%): Low flow rupture of intracavernous

aneurysm, neurofibromatosis, collagen vascular diseases andatherosclerotic diseaseOphthalmic consequences of CCF are caused by compression and

ischemia related to increased venous pressure and reduced arterialpressure.

Clinical signs commonly associated with carotid-cavernous fistulainclude proptosis in 94% cases, pulsating exophthalmos (40%), bruit(75%), fronto-orbital headache, orbital pain (40%), chemosis (71%),extraocular palsy and diplopia (60%), loss of visual acuity (46%) 5thcranial nerve involvement in 24.6 percent cases and increasedintraocular pressure and glaucoma.

Causes of Glaucoma in CCF

• Elevation of episcleral venous pressure• Elevation of orbital pressure secondary to venous stasis and edema• Secondary neovascular glaucoma• Secondary angle closure from congestion of choroids and forward

shift of lens iris diaphragm.Indirect CCF or Dural arteriovenous malformations result from

communications between branches of internal or external carotid arterywithin the dura of cavernous sinus. They are most often seen in womenover the age of 50 in association with systemic hypertension. Onset isinsidious. The patient may experience diplopia and ophthalmoplegia(often from CN VI palsy), tinnitus or orbital bruit, and a red, congestedeye that is often mistreated as an ocular infection or inflammationwith arterialized conjunctival vessels and mild proptosis.

Miscellaneous 217

Differential Diagnosis of CCF

• Cavernous sinus thrombosis• Retrobulbar hematoma• Unrecognized intraorbital foreign body with cellulitis• Tumor

Diagnosis is accomplished through neuroimaging and arterio-graphy. Contrast-enhanced CT scan and MRI will demonstrate adilated superior ophthalmic vein and cavernous sinus. Ultrasono-graphy may also demonstrate superior ophthalmic vein engorgement.Magnetic resonance angiography (MRA) is also very useful inidentifying fistulas as well as particular vessel involvement.Arteriography is still the gold standard in identifying CCF with vesselinvolvement, but due to a small risk of morbidity and mortalityassociated with this procedure, we reserve this method for potentialsurgical cases (direct rupture of the ICA in high-flow CCF or high-risk dural CCF).

Management

High-flow CCF resulting from intracavernous rupture of the ICA, in80-90 percent of cases without treatment result in blindness fromcentral retinal vein occlusion or glaucoma. Other complications thatmay be seen are epistaxis, intracerebral hemorrhage and even death99 percent treatment done by interventional neuroradiologist byplacement of intravascular coils, carotid artery ligation or finallysurgical clipping.

Indications for Treatment

• Glaucoma• Diplopia• Intolerable bruit• Severe proptosis causing exposure keratopathy• Posterior segment ischaemia.

Low-flow dural sinus CCF is very likely to resolve spontaneouslyin 20-50 percent of cases. In these cases, periodic observation is thebest therapy. For exposure keratopathy artificial tears are prescribedand diplopia managed with occlusion therapy. Watch for clinicaldeterioration that indicates that a high-risk cortical venous drainagehas developed.


CONCLUSION

Intracranial aneurysm is diagnosed with high index of suspicion thatneeds prompt referral to the neurosurgeons to facilitate earlymanagement and therapy.

BIBLIOGRAPHY

1. Amar Agarwal. Handbook of ophthalmology; Slack USA 2005.2. Bhatti, Tariq M, et al. Delayed Exacerbation of Third Nerve Palsy Due To

Aneurysmal Regrowth After Endovascular Coil Embolization Journal of Neuro-Ophthalmology. 2004;24(1):3-10.

3. Carotid cavernous fistula Indian journal of otolaryngology and head and necksurgery 2005;57:65-67.

4. Catalano RA, Simon JA, Krohel GB, et al. Functional visual loss in children.Ophthalmology 1986;93:385-90.

5. Fahle M, Mohn G. Assessment of visual function in suspected ocular malingering.Br J Ophthalmol 1989;73:651-4.

6. Gilbert, Molly E Sergott, Robert C. Intracranial aneursyms Current Opinion inOphthalmology. 2006;17(6):513-8.

7. Grant T Liu, Nicholas J, Steven L. Galetta Neuro ophthalmology Diagnosis andmanagement philadelphia, Pennsylvania; W.B. Saunders Company; 2001.

8. Headache classification committee of the international headache society:Classification and diagnostic criteria for headache disorders, cranial neuralgiasand facial pain. Cephalalgia. 1988-8 (suppl 7):1-96.

9. Hupp SL, Kline LB, Corbett JJ. Visual disturbance of migraines. Surv ophthal1989;33:221-36.

10. Kline B, Frank J. Bajandas Neuro ophthalmology Review manual: SlackIncorporated 2004.

11. Lance JW. Current concepts of migraine pathogenesis. Neurology 1993;43(suppl 1): S11-S15.

12. Miller NR, Keane JR. Walsh and Hoyt’s clinical neurophthalmology. Baltimore,Williams and Wilkins, 1998.

13. Peyman-Sanders-Goldberg-third volume-principles and practice ofophthalmology.

14. Sunita Agarwal, Athiya Agarwal, et al. Textbook of ophthalmology; Jaypee,India 2003.

15. Walsh and Hoyt’s clinical neuro ophthalmology Neil miller and Nancy Newman6th edition 1995 Lippincott Williams.

18Examination of a

Neuro-ophthalmologyCase

S Soundari

HISTORY

Examination of a neuro-ophthalmology case is crucial.1-4

• Onset of the visual loss “its progression and the severity” whetherassociated with pain

• Any history of headache, vomiting• Anyaura with the headache• Eye pain: Whether associated with visual loss• Double vision: onset, for distance and near, which direction it is

more• Involuntary movements of the eyeball• Balck outs• Color vision defect• Drooping of the eyelids: Onset, whether it is constant or variable• Any associated double vision, progression and associated features• Any field defects.

Past History

• History of medical diseases like diabetes milletus, hypertension• Whether on any drugs for long-term like ATT• Any thyroid eye disease• Myasthenia• Any treatment history like radiotherapy and chemotherapy• Any past CNS problem.

Examination

Best corrected visual acuity:The processs of examination begins with assessment of visual acuity,the most common measure of the central visual function is the best


corrected visual acuity which measure the maximal foveal spatialdiscrimination, should be obtained with refraction vision should betested for both distance and near.

Color Vision – by Pseudo-Ishihara’s Chart

Testing of color vision compliments assessment of visual acuity. Inoptic nerve disease, particularly optic neuritis, the degree ofdyschromatopsia may be proportionality greater than the degree ofsmaller visual acuity loss. In macular diseases, acuity and color visiontend to decline to corresponding degrees. Persistent dyschromatopsiais common even after recovery of visual acuity in optic neuropathy.Pseudoischromatic plates are commonly used clinically as a gross testof color vision because opticneuropathies often manifest prominentred-green defects.

Pupil Examination

• Direct light reflex• Indirect (consensual) light reflex• Swinging flash light test• Near reflex.

DIRECT LIGHT REFLEX

• The light reflex is tested in dim light with the patient looking at adistant target to neutralise the near reflex

• The bright light is brought from the side for the right eye. Thepupil will constrict to the bright light briskly

• The same is repeated now for the other eye.

INDIRECT LIGHT REFLEX

The eyes are separated by placing a hand in between the right andthe left eye. The patient is asked to fixate at the distant object. Thelight is shown to the right eye and the response is seen in the left eyeand the vice versa.

SWINGING FLASH LIGHT TEST

The test is done in dim illumination and the patient focusing at thedistance object. The examiner alternatively illuminates both eyes witha relatively bright light.

Constant distance, constant duration of the illumination and lightintensity should be maintained so that both eyes must adopt the sameconditions.

Examination of a Neuro-ophthalmology Case 221

When the pupil constricts more slowly and dilates rapidly is calledas relative afferent pupillary defect

NEAR REFLEX

Near reflex is the triad of:• Convergence• Accomodation• Constriction of the pupil.

The near reflex is tested by asking the patient to look at the distanceand to bring the focus to with in 10 cm of the eye.

Confrontation Visual Fields

Make the patient sit opposite to the examiner at 1 meter at the sameeyelevel. Patient should be able to appreciate the object used fortesting the visual fields, for the peripheral visual field.

Each eye has to be tested separately instruct the patient to coverthe left eye and look into the examiners right eye. Present the fingerin each quadrant to test quadrantanopia.

For checking the central field: Red pin is used. The pin is broughttowards the center from each quadrant and the ask the patient tocomment about when he is seeing the pin red. Ask the patient to tellagain when the red becomes faded or disappeared as the pin is movedinwards. Where the pin has disappeared from that point move thepin in all directions till it is seen in each direction. This maps out theblind spot.

For color desaturation two red objects should be presentedsimultaneously and compared.

Ocular Movements

Shine the torch light into the patients eye form from front and lookfor any obvious tropia. Look for any abnormal head posture or ptosis

Torch light can be used and it should be moved in all nine diagnosticpositions and look for any obvious deviation and nystagmus.

Saccades have to be performed both in the horizontal and verticaldirections. This is performed by showing patient fist and an objectplaced for apart. The patient is asked to look from the fist to theobject alternatingly.

Convergence: An object is moved from 50 cm towards the patient.Normal people will achieve a near point at 10 cm.

If there is any obivious deviation then diplopia charting and hesscharting are done.


Diplopia Charting

In a dark room, a red glass is placed before one eye and a greenbefore the other to distinguish their images. A bar of light through astenopalic slit in a hand torch is then moved about in the field ofbinocular fixation at a distance of at least 120 cm from the patient, thepatients head being kept stationery. The positions of the images areaccurately recorded upon a chart with nine squares marked upon it.The follow data are derived from diplopia charting of:i. The area of single vision and diplopia.ii. The distance between the two images in the areas of diplopia.iii. Whether the images are on the same level or not.iv. Whethere one image is inclined or both are erect.v. Where the diplopia is homonymous or crossed.

Test is purely a subjective one. The positions of gaze where theseparation of the images is maximal is found. In that position of gaze,the furthest displaced image belongs to the eye with the muscle palsy.

Hess Charting

To measure the degree of deviation, especially if torsional andparticularly to measure any progressive increase, the Hess screen isused.

It consists of a tangent screen marked in lines on a black cloth withspots at the intersection of 15o and 30o lines with themselves and withthe horizontal and vertical lines. The patient wears a red-green filtergoggles and holds a green light projection pointer. First red in frontof right eye. The examiner holds a red light projection pointer ontothe screen at those spots. The patient is asked to super impose thegreen light into the red light. In normal circumstances, the two pointersshould be nearly super-imposed in all nine positions of gaze. Thegoggles are then reinversed with red in front of the left eye. The eyewith the green filter is the one, which is tested.

It is useful as a prognostic guide. If the paresis of the musclepersists, then the shapes of both charts will change as follows:1. Secondary contracture of the ipsilateral antagonist will develop,

which will show up on the chart as an overaction.2. This will lead to a secondary (inhibitional) palsy of the antagonist

of the yoke muscle, which will show as underaction.With further passage of time, the two charts become more and

more concomitant, until it may be impossible to determine which wasthe primary pareitic muscle.


Nystagmus

Observe for any abnormal head posture for maintaining in the nullposition. Nystagmus to be observed in the primary position. Its planelike horizontal, vertical, rotatory or see saw to be noted. Its type likewhether it is jerky or pendular.

Its direction, the fast phase of the nystagmus and its amplitudewhether it is fine, medium or coarse.

Ocular motility is then performed and look for dampening of theamplitude with convergence when the eye accommodates. Cover testto be performed to identify manifest nystagmus.

Fundus Examination

• To look for margins—whether blurred or well defined, its colorwhether normal pink color hyperemia or pallor

• To look for abnormal vasculature like optociliary shunt• And to look into the macula for the evidence of neuroretinitis.

Visual Fields

Visual loss necessities visual field testing, which aids in localizing thelesion along the affluent visual pathway and quantifies the defect.Both kinetic and static and kinetic techniques are important. Testingmay be considered qualitative (looking for the pattern of any visualfield abnormality) or quantitative (measuring the degree of damage).

All points of the equal threshold may be connected to form anisopter. This contour map represents the outer limits of visibility.

Scotomas are areas of depressed visual function surrounded bynormal visual function. Nerve fibres from the two eyes decussate inthe chiasm. Lesions at the chiasm result in damage to the nasal crossingfibers and corresponding impairment in the heteronymous temporalvisual fields as Bitemporal hemianopia.

Lesions that injure one optic nerve at its function with the opticchiasm produce the anterior chiasmal syndrome with functionalscotoma where there is a central visual field loss in one eye accompanya supero-temporal defect in the opposite eye.

As the fibers course in the retrochiasmal visual pathway (Optictract, temporal lobe, parietal lobe and occipital lobe visual radiation).Crossed nasal fibers from the controlateral eye and uncrossed temporalfibers from the ipsilateral eye run together. Damage results inhomonymous field defects. Anterior lesions produce incongruousdefects and the posterior damage results in progressively congruousdefects.


Other Cranial Nerve Examination

First Cranial Nerve

Tested by covering each nostril in turn and presenting the patientwith familiar smell like coffee. Irritants must not be used as itstimulates the trigeminal nerve.

Second Cranial nerve

Visual acuity, pupillary reaction, visual fields, visualizing the opticnerve head.

Third, Fourth and Sixth Cranial Nerves

Examination of the ocular motility in all nine diagnostic positions.

Fifth Cranial Nerve

• Motor part is tested by palpating the temporalis and the musclesof mastigation when the patient clenches his teeth

• Sensory part is tested by checking for light touch in the threedermatomes corneal reflex to be tested.

Seventh Cranial Nerve

• Patient is asked to wrinkle his forehead, smile and blow his mouth.• Attempt to open the eyelids with eyes closed and to look for bell’s

phenomenon.

Eighth Cranial Nerve

Perform the webers and the rinne’s test by using tunning fork.

Ninth and Tenth Cranial Nerves

Gag reflex can be done. Ask the patient to say Ah and to look for anydeviation.

Eleventh Cranial Nerve

Patient should be able to shrug the shoulders against resistance andto rotate the head against resistance.

Twelfth Cranial Nerve

Make the patient put out his tongue and observe for wasting anddeviation.


CNS Examination

• Orientation to time place and person. Memory both short and longterm memory

• Tone of the muscle to be checked• Power of the muscle to be graded

— Grade 0–no movement— Grade 1–flicker movement— Grade 2–presence of movement when gravity is eliminated— Grade 3–movement against gravity— Grade 4–movement against resistance but power not full— Grade 5–full muscle power.

Reflexes

• Both superficial and deep reflexes to be elicited• Biceps, triceps, supinator and finger reflex for the upper limbs• Knee jerk, ankle jerk and babinski reflex for the lower limb.

Coordination

• Finger nose test and to look for disdiadokinesia for the upperlimb

• Getting the patient to put his heel on the shin and run it up anddown for the lower limb.

Sensation

• Pin prick and temperature• Joint and position sense• Vibration sense• Observe the patient for the gait• Spastic gait, wide based gait.

REFERENCES


2. Amar Agarwal. Handbook of ophthalmology; Slack USA 2005.3. Parson’s Diseases of The Eye-(18th ed)-Butterworth-Heinemann International

editions.4. American Academy of Ophthalmology- section 5- Neuro-ophthal 2004-2005.

19Imaging in

Neuro-ophthalmologyP Ramesh

COMPUTED TOMOGRAPHY

Principles

Computed tomography (CT) was the first modern imaging techniquewhich was able to distinguish different soft tissues by measurementof their different densities. The basis of this technique is themeasurement of different absorption values after exposure to X-rays.In the slice of interest, the absorption values of parts of a definedmatrix (so-called voxels) are transformed to gray-scale units by specificalgorithms, the reconstruction is shown on a display, and all data aresampled in a digital manner.

The absorption value is named after its inventor as the Hounsfieldunit (HU) (Hounsfield 1973). It varies linearly in proportion to theabsorption coefficient and is defined arbitrarily: thus, water is definedat 0 HU, air may have –1000 HU and less, and in bone, values of morethan +1000 HU are measured. The mean values of fat range from –20to –100 HU, cerebrospinal fluid (CSF) shows about 4–10 HU, andbrain parenchyma normally presents as 35 HU (white matter) to 45HU (gray matter).

CT, along with MRI and ultrasound (for orbital pathologies), isone of the so-called noninvasive imaging modalities. It remains themethod of choice for intracranial emergency screening, also forsuspected fractures, and when an analysis of possible bony changes,e.g., a calcification is helpful or essential for the decision of thedifferential diagnosis. The distinctly different X-ray absorption ofbone, fat, muscles, vitreous body, and lens represents a very goodnatural intrinsic contrast of the different orbital tissues.

Imaging in Neuro-ophthalmology 227

Contrast Medium

In normal extracranial parenchymal tissue (e.g., the lacrimal gland)the effect of diffusion of iodized contrast material out of the lumen ofcapillary vessel into the extracellular space is seen as increased den-sity (>10 HU). As a result of the sum of all contrast medium-filledcapillaries with an intact blood-brain barrier (BBB), the contrastenhancement of normal brain parenchyma is only 3–5 HU. The BBBrepresents a property of the pial vessel, where the tight junction oftheir capillary endothelium prevents a passive diffusion ofmacromolecules, such as water-soluble contrast medium (Sage andWilson, 1994). In case of a breakdown of the BBB, whether caused bya tumor or an infection, the continuous endothelial tight junctions aredestroyed, and the extravasation of contrast medium into thepathologic process leads to a contrast enhancement (> 5 HU).

In CT examination of the orbit, the indication of IV contrast islimited to suspected vascular lesions, as differential diagnosis is mainlyled by morphological changes. If indicated, two main contraindicationsshould be considered:1. A distinct renal impairment may lead to renal failure. The risk of

contrast agent-induced renal failure is high in dehydrated patients,in those with a known renal or cardiovascular insufficiency, andin those suffering from plasmocytoma, hypertonus, andhyperuricemia (Katzberg, 1997). Especially in patients with diabetesmellitus and an additional renal insufficiency, the risk of contrast-induced renal failure is about 9 percent (Parfrey et al. 1989).Although no absolute limiting value can be defined, the serumcreatinine should not exceed >1.5 mg/dl, and the use of nonioniccontrast agent should be standard (Schwab et al. 1989; Uder 1998).

2. In case of a manifest or known history of hyper-thyreosis, anapplication of iodized contrast material should be avoided. Ifimperatively necessary, it should be applied only after blockageof the thyroid, in order to avoid a thyrotoxic crisis, still a life-threatening disease (Kahaly and Beyer 1989). It is recommendedto start prophylactic medication at least 2–4 hours before theapplication and continue it for 14 days, at a dosage of 900 mgperchlorate per day. In patients at risk, a facultative medicationwith 20 mg Thiamazol per day can be administered additionally(Rendl and Saller 2001).A known allergic reaction to iodine represents a relative

contraindication, as short-term medication with H1- and H2-blockersimmediately before the exposure to iodized contrast medium canprevent this complication (Wangemann et al. 1988).


MRI Basic Physical and Technical Principlesof Relaxation, Special Sequences

Magnetic resonance imaging (MRI) is a method to generate cross-sectional images from the interior of the body based on the physicalphenomena of nuclear magnetic resonance without using ionizingradiation. Atomic nuclei such as those of 1H, 13C, 14Na, 19F, 23N, and31P with an odd number of protons and/or neutrons have a magneticdipole moment. Hydrogen nuclei are abundant in biological tissue, asin the hydrogen atoms of water molecules. This is the reason for theuse of hydrogen nuclei in medical MRI. Without the influence of anexternal magnetic field, the directions of the innumerable single dipolesare randomly arranged such that they cancel each other out, resultingin no macroscopic magnetic dipole moment. However, in the presenceof an external static magnetic field, the small nuclear magnetic dipolestend to align in the direction of the field, like a compass needle to themagnetic field of the earth. The nuclear magnetic dipoles are notaligned statically, rather they are staggering around the direction ofthe external static magnetic field. This phenomenon can be comparedwith the tumbling of a top around the direction of the gravitationalforce. This movement is called precession. The number of revolutionsof this precession, designated Larmor frequency, depends on themagnetic moment of the nucleus and the strength of the externalmagnetic field applied. In case of a 1.5-T MRI scanner, the Larmorfrequency of the hydrogen nuclei is 63.87 MHz. This characteristicallows the transfer of energy from an external radiofrequency pulseto the nuclei provided that the frequency is precisely the same. Thismeans that there is a resonance between the transmitter and themacroscopic oscillating magnetic moment, which acts as the receiver.During energy absorption, the precessing nuclear spin axes circumscribea cone that becomes increasingly flat. This can be illustrated as anexciting nucleus that opens its umbrella. The Brownian motion ofmolecules leads to a continuous rearrangement of the dipoles, suchthat statistically only one per million (5 ppm: parts per million) of thehydrogen nuclei are aligned with the direction of an external 1.5-Tfield at room temperature. After the termination of the appliedradiofrequency pulse, the macroscopic magnetic field returns to itsprior state by emitting simultaneously decreasing electromagneticwaves with the precessional frequency. These waves emitted duringthe relaxation are measurable and represent values which are attributedto the brightness of the individual pixels (picture elements) of whichthe images are composed by the application of sophisticatedmathematical reconstruction algorithms.


There are two types of relaxation. One is the signal decay of thesum vector parallel to the strong external magnetic field, which istermed the longitudinal relaxation or the T1 relaxation. During theT1 relaxation (spin-lattice relaxation), the excess energy is transferredfrom the nuclei to the environment (the term lattice is derived fromcrystalline solids and is used here in a broader meaning). The otherrelaxation is the signal decay of the sum signal vector perpendicularto the strong magnetic field and is designated the transverse or T2relaxation. In T2 relaxation, there is a dispersion of the primarilysynchronized precessional rotation of the spins. One can imagine thespins as an ensemble of ballet dancers, who initially obey theinstructions of the maestro and start all in the same position (they arein phase). After this moment, they show a lack of discipline, and eachballet dancer turns a little faster or slower than the others (loss ofcoherence), resulting in a random distribution of the positions (out ofphase). If we return to the spinning direction, at the beginning of thisprocess we can record the net sum vector of all synchronized (in phase)individual spins, with a rapid decay as they go off phase. The loss ofcoherence is caused by minute local magnetic inhomogeneities aroundthe macromolecules. As the adjacent spins also exchange excitationenergy with each other, T2 relaxation is termed spin-spin relaxation.Signals registered from the biological tissue depend on the water orproton concentration that can be excited and on the relaxationcharacteristics. Pure or so-called free water would show a highconcentration of excitable protons and a slow relaxation caused byonly slightly restricted tumbling of small molecules. On the otherhand, protons bound to macromolecules would show a fast relaxationby dissipating their energy to the environment and a loss of coherence.The MRI characteristics of tissue are defined by the composition ofthese components, represented in this paper in a simplified manner.Manipulation of the MRI examination parameters enables us to enhancethe differences between the local tissues, resulting in a better inherentcontrast. The terms T1-weighted (T1w), proton density-weighted(PDw) or T2-weighted (T2w) characterize MRI sequences or imagesand define the more pronounced biophysical effect of the specificimage information. Proton density (PD)–weighted images are similarto T2-weighted images, but have a shorter echo of 10–50 m and areless dependent on the relation than on the concentration of protons,i.e., water concentration in the tissue (Bösiger 1985). The fluid-attenuated inversion recovery (FLAIR) sequence combines T2-weighting and suppression of the so-called free, not tissue-boundwater.


After intravenous administration of a MRI-specific contrastmedium, such as gadopentate dimeglumine (biologically inert ascomplexly bounded gadolinium, i.e., GD-DTPA® or GD-DOTA®), adifferent take-up by tissues is seen, analogous to the iodized contrastmedium used in CT. The use of contrast medium (in T1-weightedsequences) can further improve the contrast between anatomicaldetails and also between normal and pathological tissues because ofits different signal enhancement. If these contrast-enhancing structuresare embedded in primarily hyperintense tissue (such as the extraocularmuscles, or potential lesions within the retro-orbital fat) the signalswill interfere, resulting in a loss of tissue contrast between theanatomical components. This problem can be solved using a pulsesequence that suppresses the high signal of the native hyperintensetissue. In the case of fat, the sequence is designed to be fat-suppressed(FS). Special MRI protocols enable a differentiation of flowing bloodfrom nonmoving tissue (so-called stationary tissue), the basis for MRangiography. In MR angiography, the signal of stationary tissue issuppressed and the signal of flowing blood is enhanced, without anyapplication of contrast material.

The so-called diffusion-weighted MRI (DWI) is able to imagemolecular diffusion. Tissue-bound water has a restricted moleculardiffusion compared with free water, due to frequent collisions withmacromolecules, in particular proteins. Therefore, tissues with adifferent viscosity and a different ratio of intra- and extracellularspaces show different diffusion properties. For this reason, diffusion-weighted MRI discriminates reliably an arachnoid cyst filled withfree water and an epidermoid tumor of solid tissue whereas in con-ventional sequences, liquor and epidermoid tumor can both give thesame signal intensity (Laing et al. 1999; Gizewski 2001). The so-calledanisotropic diffusion of water molecules in the fiber pathways, whichis much more restricted across the fibers than along them, can also beimaged in different planes (Hajnal et al. 1991). Diffusion-weightedMRI can disclose an acute infarction at a very early stage, and in thecase of elderly patients with multiple chronic infarctions, it helps touncover additional new lesions (Schaefer 2001). It also seems thatdiffusion-weighted sequences image a cystic tumor different to thecentral colliquation of an abscess, so offering an additional tool in thedifferential diagnosis (Kim et al. 1998).

Along with a strong and very homogeneous main magnetic fieldand all devices (antennas or coils) to excite the protons by aradiofrequency pulse and to receive the electromagnetic waves emittedfrom them, there is a need for a space-encoding system. Temporary,


superimposed, magnetic gradient fields cause changes of the Larmorfrequency and the phase of spin populations in small volumes (voxels),with a precise local attribution. Where the magnetic field is stronger,the precessional frequency is higher, and where the magnetic field isweaker, the frequency is lower. It is possible to identify the locationof signal generating spin pools by small space-encoded differences ofthe frequencies, like distinguishing radio stations. Additional space-encoded different phases of precessing spin pools are used.

For more superficially located structures, such as the orbits, theimage resolution can be optimized by using phased-array surface coilsinstead of the conventional head coil. Surface coils are speciallydesigned antennas, which can be applied near the region of interestand fades out disturbing signals from the environment. In case of anexamination of the orbit, they are placed obliquely over both orbits,in order to lighten the orbital apex. It should be emphasized that arelatively small unilateral surface coil (with a diameter of about 4 cm)applied anteriorly over one orbit is only suitable for imaging theipsilateral globe and does not provide a more posterior “illumination”.

Restrictions

Ferromagnetic Material, Pacemaker, Neurostimulator, VentricularShunts with magnetically adjustable valves.

When approaching the temperature of absolute zero, no electricalresistance as e.g., in the coil of the electric magnet is found. For thisreason, the most frequently used modern high-field MRI scanners(0.5–1.5 T) today are based on a superconducting coil of the mainmagnet, a system with a liquid helium-cooled main coil.

This strong main magnetic field necessitates a few precautions.Patients with ferromagnetic implants, e.g., older aneurysm or othervessel clips, pacemakers, neurostimulators, and traumatically incorpo-rated metallic-ferromagnetic foreign bodies (e.g. debris arising fromworking with metal, or old shell splinters), should not be exposed tohigh-field MRI. In addition to the image quality disturbance causedby the so-called susceptibility artifacts of the ferromagnetic material(Lüdeke et al. 1985) this can endanger the patient (Kanal and Shellock1993). Whereas metal devices fixed on bone do not present a dangerif exposed to MR, ferromagnetic foreign bodies, or clips in the lung,abdomen, eye, and adjacent to vessels can twist due to the strongmain magnetic field and lead to a life-threatening complication.Ventricular shunts with transcutaneous magnetically pressure-adjustable valves (Medos and Sophy valves) can be maladjusted inMRI, and therefore the systems have to be checked radiologically


after MRI (Miwa et al. 2001; Ortler et al. 1997). As new magnet-compatible devices (Wichmann et al. 1997) have only been developedin the last decade, MRI is still unavailable to most patients with animplanted pacemaker or neurostimulator. The problems are not onlycaused because of the fact that these devices are usually magneticallyprogrammable, there is an additional risk from the electrodes, whichcan act as antennas and interact with the changing electromagneticfields. One must be always absolutely certain about the individualpatient’s magnet compatibility, probably with the result of a rejectionof the patient for MRI if there remains any doubt.

Claustrophobia, Sedation, Surveillance

To perform a MRI examination, it is necessary to bring the entirepatient into the narrow shaft of the equipment, as the optimalhomogeneity of the magnetic field is in the center of the magnet.Even for an examination of only the head or the orbit, the patient hasto be placed deep inside the MRI. This is mainly a problem forclaustrophobic patients, and thus they need sedation before the MRIexamination. However, a sedated patient placed in this narrow tunnelis not accessible. In case of deep sedation, special magnet-compatiblemonitoring devices are needed for surveillance, including at leastessential peripheral pulse oximetry. In MRI, the acquired data are notseparately sampled sections, as for CT, but the data sampling issimultaneous for all sections of one sequence and the acquisition timedepends on the examination parameters, e.g., the repetition timechosen. Therefore, one MRI sequence may last only a few minutes oreven more than 10 min. If the patient moves during this time, a loss ofimage quality of all sections results. During MRI of the orbit, thepatient should keep the eyes open and try to maintain a midline restingposition. Consequently, in the case of uncooperative patients, whoare not able to remain motionless, the quality of the images will beimpaired.

Optic Pathway Pathology

• congenital pathology/infantile presentations• acquired optic pathway lesions• work-up in systemic diseases• unexpected (incidental) fi ndings

Any neuroimaging procedure should be based on profound clinical(including ophthalmological if appropriate) examination. This shouldallow the neuroradiologist to formulate specific questions.


CONGENITAL PATHOLOGY OF OPTIC PATHWAYS

Infantile Presentations

Micro-ophthalmos/Anophthalmos

Uni- or bilateral micro-ophthalmos/anophthalmos may be seen invarious conditions (Albernaz et al. 1997; Nelson et al. 1991).Neuroimaging is performed to assess orbital anatomy, optic chiasm,and posterior visual pathways as well as possible brain malforma-tions Aicardi syndrome, observed only in girls, is considered to resultfrom an X-linked mutation that is lethal in boys. The relevant triadconsists of a typical optic disk appearance with “chorioretinal lacunae”,infantile spasms, and agenesis of the corpus callosum (Aicardi 1992;Brodsky et al. 1995). In addition, other central nervous systemmalformations are always present, in particular migration anomalies(heterotopias, polymicrogyria) and midline arachnoid cysts.

Ocular Tumors

Retinoblastoma is the most common intraocular tumor in infancy,affecting about 1 in 20,000 infants. The most frequent presentingsymptom is leukokoria, also called “cat’s eye reflex”. Leukokoriagenerally represents an advanced stage of the disease. Computedtomography (CT) (Fig. 19.1) displays punctate or more homogeneousareas of calcification in 95 percent of retinoblastomas (Barkovich 1995).Contrast enhancement of tumor tissue is generally found. Contrastenhancement is also demonstrable with MRI. T1-weighted imagesreveal the tumor as hyperintense, T2-weighted images usually as ahypointense mass Proton density images may assist in the demarcationof the tumor. MRI can occasionally provide evidence of distal opticnerve infiltration. A large proportion of retinoblastomas are geneticallydetermined, and about a third occurs bilaterally. When tumoros tissueis also demonstrated in the pineal region by neuroimaging, it is termedtrilateral retinoblastoma. This may already be present on initialevaluation.

Spasmus Nutans

So-called spasmus nutans typically presents at 6–12 months withdisconjugate nystagmus, torticollis, and findings have been seen ingirls.


Other White Matter Disorders

Apart from PMD, other dysmyelinating conditions can present withcongenital nystagmus. The exact genetic/biochemical basis of theserare conditions is still unknown.

Septo-optic Dysplasia

Septo-optic dysplasia (SOD) typically presents as congenitalnystagmus. Fundus examination reveals bilateral optic nervehypoplasia. In addition, the syndrome consists of an absence of theseptum pellucidum (Hypothalamic-pituitary dysfunction is present ina minority of patients, presenting as neonatal hypoglycemia and/orgrowth retardation (Sorkin et al. 1996). The prognosis is quite variable,ranging from blindness to useful vision. Affected children may bementally retarded. In some children, additional CNS malformationscan be found, in particular hypoplasia of the corpus callosum andcortical dysplasia (Sener 1996). SOD is unlikely to be a homogeneousentity. Hypoplasia of the optic nerves and absent septum are alsoseen as part of the holoprosencephaly complex (Barkovich 1995). Theseptum pellucidum is also mostly missing in rhombencephalosynapsis.It is suggested that SOD is a vascular disruption sequence (Lubinsky1997).

Figs 19.1: CT scan showing trilateral retinoblastoma


Optic Nerve Hypoplasia

Hypoplasia of the optic nerves may be unilateral or bilateral (Figs19.2 and 19.3). It is not a clinical or pathogenetic entity. We have seenseveral children with unilateral optic nerve hypoplasia presenting tothe ophthalmologist with “poor vision” or strabismus. The intracranialanterior optic pathways are usually markedly asymmetric, butadditional anomalies are exceptional.

Figs 19.2A and B: (A) Axial, (B) coronal T2-/FSE MRI of a 3-month-old-girl withoutvisual fixation. Absent septum pellucidum and almost no identifiable optic nerves.Diagnosis: septo-optic dysplasia

Figs 19.3A and B: Patient clinically blind at 1 year (A) Axial, (B) coronal T2-/FSEMRI of a 4-year-old boy. Clinically convergent strabismus and bilateral optic nervehypoplasia. MRI shows absent septum pellucidum. Diagnosis: septo-opticdysplasia


Periventricular Leukomalacia

Periventricular leukomalacia (PVL) is a well-known complication ofprematurity before 34 weeks’ gestational age. PVL affects primarilythe posterior part of the hemispheric white matter. Clinically, it maygo along with spastic diplegia type of cerebral palsy and is oftenaccompanied by delayed visual development (Jacobson et al. 1996;Lanzi et al. 1998; Olsen et al. 1997).

MRI allows the detection of specific residual findings: variablereduction of periventricular white matter predominantly involvingthe posterior aspects, increased size of lateral ventricles, often withan irregular contour (evacuo). The remaining white matter often showsincreased T2 signal, presumably corresponding to gliosis.

Multiple Sclerosis

It is estimated that about 2 percent of patients with multiple sclerosis(MS) present during childhood. Presenting symptoms may be variablesuch as muscular weakness, gait abnormalities, visual symptoms, andseizures (Ghezzi et al. 1997; Hanefeld 1992). Imaging findings inpediatric MS are not considered to be different from those in adults(Barkovich 1995).

Acute Disseminated Encephalomyelitis

Acute disseminated encephalomyelitis (ADEM) or parainfectiousencephalomyelitis is considered an autoimmune response. Thishypothesis is supported by the fact that the gross pathologic andhistologic manifestations resemble those of experimental allergicencephalitis. ADEM involves primarily white matter but can also affectcortical and deep gray matter. Children typically develop acute focalneurologic signs and/or seizures late in the course of a viral illness orpost vaccination). Neuroimaging reveals usually multiple foci of T2hyperintensities; these may be circumscribed, confluent, oroccasionally affect white matter diffusely (Murthy 1998). Variouspatterns of contrast enhancement may be found in the acute/subacutephase. Differentiation of MS from ADEM is not always possible inthe beginning. The prognosis of ADEM is favorable as a rule, leadingto complete clinical recovery, both from the clinical and theneuroimaging points of view. Occasionally, sequelae can be found.

Trauma (Nonaccidental Injury)

Injuries to the optic pathways due to head trauma will not be discussedhere. However, we would like to point to so-called nonaccidental


injury by shaking infants less than 6 months of age. The typicalpresentation is impaired consciousness and convulsions, often result-ing in status epilepticus. Typically, bilateral retinal hemorrhages arepresent. Extensive cerebral damage in this condition usually resultsin permanent neurological sequelae including visual impairment oreven cortical blindness (Ewing-Cobbs et al. 1998). The neuroimagingcorrelation in the acute stage is not spectacular, with evidence of brainswelling and often some interhemispheric blood accumulation. Follow-up neuroimaging as a rule demonstrates extensive cerebral atrophy.

Neurofibromatosis Type 1Neurofibromatosis type 1 (NF1) is an autosomal dominant disorderdue to mutations in the very large NF1 gene at chromosome 17q11.About 50 percent of patients have new germ-line mutations, i.e. theyhave no positive family history. The prevalence in most populationsis about 1:4000 individuals. As is evident from the listing of diagnosticcriteria optic pathway glioma (OPG) is such a criterion. OPG are tumorsof infancy; in larger series, the mean age at diagnosis is 4–5 years(Figs 19.4A and B).

Diagnostic criteria for neurofibromatosis type 1 The presence of twoor more of the following is diagnostic:1. Six or more café-au-lait spots, greater than 5 mm in diameter in

prepubertal children and over 15 mm in post-pubertal individuals.2. Two or more neurofibromas of any type, or one plexiform neurofi

broma.3. Axillary and/or inguinal freckling.4. Optic nerve glioma.5. A distinctive osseous lesion, such as dysplasia of the sphenoid

wing, thinning of long bone cortex, with or without pseudarthrosis.6. A first-degree relative (parent, sibling, or offspring) with NF1

according to the above criteria.OPG are pilocytic astrocytomas. It is important to distinguish

astrocytomas from benign lesions commonly encountered in NF1: T2hyperintensities are often found in the basal ganglia (particularlyglobus pallidus), brainstem, and cerebellum, not enhancing withcontrast and not having space-occupying effects.

Mild proptosis is not uncommon in NF, even in the absence of anoptic nerve glioma. It can be related to sphenoid wing dysplasia, butoften no obvious explanation is evident.

Neurofibromatosis Type 2Neurofibromatosis type 2 (NF2) is an autosomal dominant disorderdue to mutations at chromosome 22q12. The involvement of the brain


structures in NF1 and NF2 are quite different: While NF2 consistentlyaffects the acoustic/vestibular nerve, this is never encountered in NF1.NF2 is not associated with optic pathway gliomas.• Diagnostic criteria for neurofibromatosis type 2. The following are

diagnostic:1. Bilateral vestibular schwannomas; or2. A first-degree relative with NF2 (Figs 19.5A and B), and either a

unilateral vestibular schwannoma or two of the following: menin-gioma (Figs 19.6A and B), schwannoma, glioma, neurofibroma,posterior subcapsular lens opacity, or cerebral calcification; or

3. Two of the following: unilateral vestibular schwannoma multiplemeningiomas either schwannoma, glioma, neurofibroma, posteriorsubcapsular lens opacity, or cerebral calcification.

INTRACRANIAL PATHOLOGY OF THE VISUAL PATHWAY

Intrinsic Lesions, Glioma in Adults

The term glioma stands for the corresponding three types of glialcells. The three major types of gliomas originate from: astrocytomaoligodendroglioma and ependymoma and the so-called mixed gliomasthat contain two or more different cell types in varying proportions,most frequently primarily oligoastrocytoma (Okazaki 1989), whereasintraventricular choroid plexus papilloma and carcinoma are distinctfrom ependymoma (Kleihues and Cavanee 2000).

Figs 19.4A and B: (A) Sagittal T1-weighted, MRI of a 26-year-old patient withNF1. (B) Asymmetrical optic chiasm glioma known for 12 years


Figs 19.5A to D: T1-weighted, contrast-enhanced MRI of newly diagnosed NF2 ina 14-year-old girl. MRI shows bilateral acoustic neuromas, meningioma at tip ofleft temporal lobe, mass (presumably a meningioma) in suprasellar/left parasellar/sphenoid area

Figs 19.6A and B: (A) Axial plain CT, (B) axial CT following administration ofcontrast medium in a 14-year-old-patient prompted by new onset of diplopia.Plain CT reveals calcifying right optic nerve sheath meningioma. Following contrast:left frontal meningioma


Extra-axial TumorsDue to the fact that extrinsic (or extra-axial) tumors are frequentlybenign, the treatment and prognosis are based upon the correctdiagnosis of suspected intracranial extrinsic masses. The use of MRIis mandatory for these tumors because it has the ability to differentiatethe boundary between the brain parenchyma and the mass itself. Thesuperior contrast resolution and multiplanar imaging capacity of MRIenable the identification of anatomic markers as cardinal features ofan extra-axial lesion. Instead of the demonstration of the tissue contrastof extrinsic masses and brain parenchyma, the definition of boundarylayers between the tumor and the brain surface permits the diagnosisof an extra-parenchymal intracranial lesion. The boundary layersrepresent cerebrospinal fluid (CSF), pial blood vessels, and/or thedura. CSF clefts are recognized as crescentic bands, frequently onlyover a portion of the tumor, with signal intensities similar to those ofspinal fluid: low on T1-weighted, isointense on proton density-weighted, and high on T2-weighted images. In SE sequences, bothnormal anatomic and pathologic vessels are identified as rounded orcurvilinear signal voids at specific locations of the lesion margin. Theuse of i.v. contrast agents enables the demonstration of thecompartmentalization of extrinsic lesions, since a large number oftumors show a specific pattern, including extensive signal enhancement(meningioma, metastasis), while others show none (epidermoid anddermoid tumors) (Goldberg et al. 1996).

MetastasisIntracranial metastasis or secondary brain tumors are defined astumors involving the CNS and originate from, but are discontinuouswith, primary systemic neoplasms. They account for 15 to 30 percentof all intracranial tumors in pathologic series (Okazaki 1989; Nelsonet al. 2000). The most frequent primary malignancies include lungcarcinoma (40% metastasize to the brain), breast carcinoma (roughly25 percent metastasize to the brain) (Figs 19.7 and 19.8),hypernephroma, melanoma, and neuroblastoma, the latter occurringpredominantly in children.

All areas of the brain may be affected, with preference for thecorticomedullary junction as the starting point (Okazaki 1989), possiblydue to greater capillarization of this region (Zülch 1986). The sellarregion is the preferred location for hematogenous spread of primarycarcinoma of extracranial origin. In addition to the convexity of thebrain and/or cerebellum, leptomeningeal tumor cells deposit in therecess of the third ventricle but may also invade the parenchyma ofthe hypothalamus and/or chiasm.


Fig. 19.7: A 35-year-old woman with acute vision loss, predominantly of the righteye, and a history of breast carcinoma. Diagnosis: intra- and suprasellar metastasis.MRI: Axial T2-weighted FLAIR sequence showing edema of the chiasm and bothoptic tracts

Figs 19.8A to D: A 38-year-old-woman with chiasm syndrome, diabetes insipidus,and a history of breast carcinoma. Diagnosis: hypothalamic and chiasmalmetastasis of breast carcinoma. T1-weighted MRI: (A) Axial native view showinga slightly hypointense lesion dorsal to the chiasm with apparent invasion.(B) Corresponding contrast-enhanced view, identifying invasion of the chiasmand the proximal optic tracts. (C) Coronal native view. (D) Midsagittal contrast-enhanced view, demonstrating metastatic spread throughout the hypothalamusand pituitary stalk (D with permission of Müller-Forell 2001)


SELLAR TUMORS

Corresponding to the various tissues, a number of pathologic processesmay occur. More than 30 different pathologic entities, primarilyextrinsic lesions, involving and affecting structures of the sellar andjuxtasellar region have been described (Osborn and Rauschning 1994).These tumors involve the brain parenchyma secondarily and are oftencured completely without recurrences even if the lesion has reached aconsiderable size. Intrinsic brain tumors, which often show a recurrentclinical course even for benign tumors, develop less frequently in thesellar region.

Gliomas of the Chiasm

Gliomas of the anterior visual pathway, histologically defined aspilocytic astrocytoma are uncommon lesions, but account forapproximately 65 percent of intrinsic tumors of the optic nerve. Theselesions most frequently occur in children in the first decade of life(Dutton 1994), whereas only 10 percent present in patients older than20 years (Wulc et al. 1989). As most of these gliomas are located in theintraorbital and intracranial part of the optic nerve (Fig. 19.9),additional involvement of the chiasm is seen in about 75 percent ofpatients However, only 7 percent occur in the chiasm itself, and 46percent involve both the chiasm and hypothalamus the latter increasingthe mortality rate to over 50 percent, since no specific therapy altersthe final outcome (Dutton 1994).

They are not associated with NF 1 and uniformly show a fatalcourse of usually less than 1 year (Rush et al. 1982; Mason and Kandal1991; Dutton 1994; Hollander et al. 1999).

Imaging Characteristics: MRI as the method of choice relaxation times.In macroadenomas, MRI enables a high anatomic resolution anddefinition of the neighboring tissue, i.e. intracranial optic nerves,chiasm, and cavernous sinus. In most cases, native, non-contrast-enhanced images allow accurate and conclusive differentiation of thetumor and deformed, compressed, flattened visual structures of theoptic of the pre- and post-contrast images does not routinely enablethe definite prediction of tumor invasion of the cavernous sinus. Onlya carotid artery encasement or an extension lateral of the cavernoussinus towards the temporal lobe is a reliable indicator of cavernoussinus invasion.


Figs 19.9A to F: MRI: (A) Axial T2-weighted view with a very large, space-occupying,isointense lesion located in a widened suprasellar cistern, depressing and spreadingthe basal vessels, (B) Coronal T1-weighted native view demonstrating pressureexertion on the widened third ventricle by the central hypointense (necrotic) tumor,(C) Midsagittal, T1-weighted, contrast-enhanced view with demarcation of theentire enhancing tumor, compressing and displacing the brainstem, and extendinginto the posterior fossa. Note widening of the entrance of the otherwise normallyconfigured sella (arrow), (D) Coronal native view with intra- and suprasellar lesionand inferior chiasmal compression. Note the slightly hypointense signal in thesphenoid sinus, (E) Corresponding contrast-enhanced view with inhomogeneouscontrast enhancement of the intra-/suprasellar, apparently encapsulated lesion,but homogeneous enhancement in the sphenoid sinus. CORR = Sponding tosinus inflammation, note the small leptomeningeal enhancement at the base ofthe left frontal lobe (arrow), (F) Axial contrast-enhanced view with necrotizing,encapsulated tumor and leptomeningeal enhancement of the basal frontal sulci(arrows)


Meningiomas

Meningiomas (Fig. 19.10) associated with hereditary tumor syndromesuch as schwannoma (i.e., in patients with NF2) (Woodruff et al. 2000)mainly occur in younger patients. Approximately 20 percent ofmeningiomas are located in the sellar region, with 50 percent arisingfrom midline structures such as the sphenoid plane tuberculum sellaediaphragm sellae, or the dura of the cavernous sinus Globularmeningiomas of the suprasellar or paraclinoid region may produceearly ophthalmological symptoms because of optic nerve.

Figs 19.10A to C: MRI: (A) Axial view in the region of the chiasm, visualizing thesuperior region of the right sphenoid wing meningioma and an ipsilateral temporalmeningioma. Note the susceptibility artifacts after left temporal craniotomy.(B) Coronal view at the cavernous sinus, showing the entire circumference of themeningioma of the right anterior clinoid process. Note the left temporobasalparenchyma defect after initial surgery. (C) Coronal view in the region of thechiasm with tumor extension to the right chiasmal region. Another frontalmeningioma is demarcated in addition to the known temporal meningioma orchiasmal compression and therefore do not normally exceed 2 cm in diameter


Imaging Characteristics: Due to their high cell density andpsammomatous calcification, meningiomas of the sellar region presenton CT as isodense to hyperdense midline lesions. Diffuse hyperostosisis particularly apparent on CT images of en plaque meningioma). Aperifocal edema is detected only in the rare cases where the cerebralcortex is destroyed by this tumor Apart from the differentiation ofpituitary adenomas, where a trans-sphenoidal approach is thepreferred operative procedure, the most important question forneurosurgeons is the possible invasion of the cavernous sinus and/ornarrowing of the ICA, which is best addressed by MRI.

Craniopharyngioma

They are assumed to arise from Rathke’s pouch epithelium and accountfor 1.2-4.6 percent of all intracranial tumors and thus represent thesecond most frequent tumors of the sellar region after pituitaryadenomas. Craniopharyngiomas (Figs 19.11A to D) show no sex biasbut a bimodal age distribution, with one peak involving children andadolescents and another one involving adults (Adamson et al. 1990;Crotty et al. 1995). A clinicopathologic distinction is made betweenadamantinous and papillary craniopharyngioma. Most adamantinomasare hormone-inactive lesions and present as solid tumors with avariable, at times predominantly cystic component, containingcholesterol-rich, thick, brownish-yellow fluid with the appearance ofmachine oil.

Imaging Characteristics: CT in the axial and coronal views is still justifiedfor the basic and differential diagnosis of craniopharyngiomas, in viewof the characteristic calcification of parts of the tumor seen in 50-70%of cases Even in the absence of calcification, the solid tumor partsappear hyperdense with prominent contrast enhancement, whereasthe cysts seem isodense to CSF and may show enhancement of thewall MRI enables superior delineation of the tumor extent, especiallyon the coronal and sagittal views Morphology and signal patterns aremarked by great variety: adamantinous craniopharyngioma primar-ily shows a combination of T1-weighted hypoin-tense and T2-weightedmassive hyperintense signal character, (whereas in papillarycraniopharyngioma, a hyperintense signal on T1-weighted andhypointensities on T2-weighted sequences may dominate. The solidtumor parts of both types generally show a hyperintense signal onT1-weighted images and prominent enhancement of the tumor andcyst wall).


Astrocytomas

Astrocytic tumors, represent the most frequent entity of primary braintumors with up to 60 percent of all intracranial neoplasms and com-prise a wide range of age and gender distribution, growth potential,extent of invasiveness, morphological features, tendency forprogression, and clinical course (Okazaki 1989; Cavanee et al. 2000).Astrocytomas primarily manifest in adults and may arise at any siteof the CNS, exhibiting a wide range of histopathological features and

Figs 19.11A to D: (A) Coronal, T1-weighted, contrast-enhanced image with caudaldepression of the third ventricle by the predominantly suprasellar, cystic tumor.The contrast-enhanced capsule is visualized, while the chiasm is not seen.(B) Midsagittal view with differentiation of the pituitary stalk (star). Note thedepression, dislocation, and deformation of the brainstem. (C) Axial T2-weightedimage demonstrating the high proton content (high signal) of the oily fluid contentof the cystic tumor region. Note the deformed brainstem. (D) Corresponding T1-weighted, contrast-enhanced image where a remnant of the chiasm (confirmedon operation) is seen at the medial right tumor surface (arrow)


biological behavior. Astrocytomas include, e.g. pilocytic and subepen-dymal giant cell astrocytoma (both WHO I), diffuse low gradeastrocytoma (WHO II), anaplastic astrocytoma (WHO III), andglioblastoma (WHO IV). These different entities reflect the type andsequences of genetic alterations acquired during the process oftransformation, where the progression from low grade to anaplasticastrocytomas and glioblastomas is associated with the cumulativeacquisition of multiple genetic alterations (Cavanee et al. 2000).

Pilocytic Astrocytoma (WHO I)

Pilocytic astrocytomas (WHO I) should be differentiated from diffusegrowing astrocytomas as they are more circumscribed, slow-growinglesions with different location, morphology, genetic profile, andclinical behavior.

High Grade Glioma

Diffuse astrocytoma (WHO II) is characterized by a high degree ofcellular differentiation, slow growth, and diffuse infiltration of theadjacent brain structures. It has a tendency for malignant progressionto anaplastic astrocytoma and, ultimately, glioblastoma). Most of thesepatients are adults (presenting with seizures and clinical symptoms,depending on the localization.

Imaging Characteristic: Although most glial tumors arise from a segmentof only one gyrus (Yasargil 1994), the affected parenchyma (usuallywhite matter, but an involvement of gray matter is often seen)demarcates an ill-defined area, hypodense on CT. On MRI,astrocytomas mostly present as mildly hypointense on T1-weightedand hyperintense on T2-weighted, due to the fact that they representa degenerative microcystic formation, filled with clear fluid, and anirregular, not always clearly distinguished perifocal edema.

Metastasis

Secondary lesions should always be included in differential diagnosticconsiderations of extrinsic and even intrinsic tumors of the sellarregion, particularly with a view to the capacity of some primarilyextracranial tumors to involve the skull base (percontinuitatem) or behematogenous. Metastases involving the cavernous sinuspredominantly arise from malignant tumors of the nasal cavity,growing perineurally or perivascularly via the basal foramina.


Imaging characteristics are nonspecific and similar to thoseencountered in more common tumors of the sellar region.

Cavernoma (Syn. Cavernous Hemangioma)of the Cavernous Sinus

They present as well-defined tumorous lesions with a homogeneous,intermediate signal on T1-weighted views, a hyperintense signal onT2-weighted sequences, and homogeneous, massive enhancementafter gadolinium administration.

The Tolosa-Hunt syndrome

The Tolosa-Hunt syndrome (THS) is an inflammatory disease ofunknown origin, limited to the superior orbital fissure and thecavernous sinus (Smith and Taxdal 1966). The presentation of cranialnerve paresis of one or several of the cranial nerves passing thecavernous sinus (N III, N IV, N VI, and N V1) may coincide with theonset of orbital pain or follow it within a period of up to 2 weeks. Thepain must be relieved within 72 hours after steroid therapy. Althoughhigh resolution CT or MRI can neither exclude nor confirm THS whena lesion compatible with an inflammatory process is visualized, othercausative lesions as, e.g. a malignant tumor must be excluded.

Clinical and neuroradiological follow-up must be done for at least2 years, even in patients with negative findings on imaging at onset.

Cystic Lesions

In the differential diagnosis of suprasellar tumorlike lesions, arachnoidcyst and epidermoid cyst play some important role, along withRathke’s cleft cyst and hypothalamic hamartoma.

Rathke’s cleft cyst, a benign epithelium-lined cyst arising fromremnants of Rathke’s pouch, may become symptomatic in the case ofintra-and suprasellar extension, a rather rare condition (Rose et al.1992). On MRI, signal intensities vary with cyst content from serousto mucoid (Osborn 1994b).

Arachnoid cysts account for about only 1 percent of all intracranialspace-occupying lesions, but 10 percent arise in the suprasellar region(Armstrong et al. 1983). Arachnoidal cysts are filled with CSF; theetiology of these mainly congenital lesions remains poorly under-stood and controversial, but meningeal mal-development is preferred,so that minor aberrations of CSF flow through the loose, primitive,perimedullary mesenchyme are considered to result in a focal splittingof leptomeninges and the formation of a diverticulum or blind pocket


within the arachnoid membrane (Schachenmayr and Friede 1979;Becker et al. 1991). As an arachnoid cyst is a well-defined, sharplydemarcated, extra-axial formation filled with CSF, MRI signal char-acteristics correspond with hypointense signal on T1-weighted andhyper-intensity on T2-weighted images.

Epidermoid cysts probably arise from inclusion of ectodermalepithelial elements at the time of neural tube closure (accounting for0.2–1% of all primary intracranial tumors, 7 percent of them in thesuprasellar region (Osb or n 1994b). Imaging of these well-delineated,tumor-like cystic lesions is not always able to differentiate them fromarachnoid cyst, especially since the MRI signal intensities are similarto CSF in every conventional sequence. DWI confirms the diagnosis.

Multiple Sclerosis

The onset of MS usually occurs in patients aged from 20 to 40 years(15% before 20 years of age, 10 percent after 50 years) with a femalepredominance. Most often, the first and only clinical symptom consistsof impaired vision, presenting as retrobulbar neuritis (RBN), followedor combined with fluctuating periods of sensomotoric or gaitdisturbances. The clinical course of disease progression can be dividedinto a relapsing-remitting and a chronic progressive form (Heaton etal. 1985). For the diagnosis of MS recently published new guidelineson diagnostic criteria of MS enable the physician to define the diagnosisfor MS, possible MS or nor MS, replacing the diagnostic criteria ofPoser et al from 1983 (McDonald et al. 2001). These guidelines includethe evidence of dissemination in time and space of lesions typical forMS, objectively determined with clinical and imaging signs. Theobtained imaging criteria for MS should require evidence of at leastthree of the four following findings:1. One gadolinium enhancing lesion or nine T2-hyperintense lesions

if there is no gadolinium enhancing lesion,2. At least one infratentorial lesion,3. At least one juxtacortical lesion,4. At least three periventricular lesions. Additional fi ndings of CSF

abnormalities with the presence of autochtone IgG production(oligoclonal bands) (McLean et al. 1990), lymphocytic pleocytosis,and abnormal VEP, typical for MS (delayed but with well preservedwave form) provide supplement information (Halliday 1993) toclinical finding of neurological disturbances typical for MS.

Imaging Characteristics: MRI is the imaging tool of choice in suspecteddemyelinating disorders (Sartor 1992; Osborn 1994f; vander Knaap


and Valk 1995a; Edwards-Brown and Bonin 1996; McDonald et al.2001). Although the sensitivity in detecting MS lesions is about 85percent (Lee et al. 1991), the correlation of neurological symptomsand localization of imaging findings is generally poor as most foci areclinically silent (Barkhof et al. 1992), but in some cases a correlation ofclinical and imaging findings is probable The imaging protocol shouldinclude axial and sagittal PD/T2-weighted and FLAIR sequences,where the demyelinated areas demonstrate a high signal (Filippi et al.1999a; Reiche et al. 2000). The sagittal view is best in order to showthe characteristic periventricular/ pericallosal, ovoid lesions (so-calledDawson’s finger), caused by the centripetal course of the medullaryveins, representing the perivascular inflammation (Horowitz et al.1989). T1-weighted native and contrast-enhanced sequencesdemonstrate acute or recurrent inflammatory lesions, which normallyenhance contrast media, caused by BBB disruption (Paty 1997; Fazekaset al. 1999; Reiche et al. 2000). involvement including the optic chiasmand nerves is the most common site of affection (Mirfakhraee et al.1986; Okazaki 1989).

Depending on the character of the lesions (solitary, multiple, ordiffuse disseminating), imaging findings may resemble multiplesclerosis, systemic lupus erythematosus (SLE), non-Hodgkinlymphoma (NHL) or even inflammatory affections like tuberculousmenengitis) (Edwards-Brown and Bonin 1996; Woitalla et al. 2000).As periventricular signal intense lesions are seen in about 50 percentof the patients, the differential diagnosis from multiple sclerosis maybe difficult, but a possible additional leptomeningeal involvementmakes the diagnosis of sarcoidosis more likely (Hayes et al. 1987;Zajicek et al. 1999; Woitalla et al. 2000). In solitary or multiple lesionswhich often demonstrate a contrast enhancement and show apreference for the diencephalon (the floor of the third ventricle,hypothalamus) and suprasellar region, solid tumors of the suprasellarregion should be taken into consideration in the differential diagnosis,along with multiple metastasis, NHL, or Langerhans’ cell histiocytosis67 percent of patients with sarcoidosis, leptomeningeal and/orependymal involvement is found.

Toxoplasmosis

Corresponding to pathological changes, a “target” appearance of thesolitary or multiple ringenhancing masses with perifocal edema iscommon. Rim or focal nodular enhancement following contrastadministration are seen on CT and also on MRI. The most important,


but sometimes hardly distinguishable differential diagnosis is fromprimary CNS lymphoma (Dina 1991). While a periventricular locationand subependymal spread favor lymphoma, more than one lesion,preferentially adjacent to or in the region of the basal ganglia, maketoxoplasmosis likely (Osborn 1994g).

Acute Disseminated Encephalomyelitis (ADEM)

In contrary to multiple sclerosis, ADEM is characterized by an acutemonophasic disorder, predominantly occurring following a viralinfection or vaccination with a mean latent period of 4-6 days or severalweeks; sometimes it is seen without recognized antecedent. ADEMmay occur at any age, but shows a preference for children or youngadults (Consequently, the simultaneous occurrence of polytopicneurological symptoms such as hemi-, di- or tetraplegia, cerebellarataxia or cranial nerve palsies, combined with optic neuritis andbladder dysfunction, may lead to the correct diagnosis.

As in all demyelinating diseases, MRI shows best the mainlysubcortical, confluent, bilateral but slightly asymmetric hyperintensefoci on T2-weighted images. Consequently, along with themonophasic clinical symptoms, if BBB disruption is apparent, a similarenhancement of the lesion is seen, in contrast to MS, where only acutefoci show a T1 time shortening with signal enhancement.

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A

Abducent nerve 132clinical features

deviation 135diplopia 135head posture 135ocular movements 135

course 132cavernous sinus 134orbit 134superior orbital fissure 134

exit from the brain 132lesions 136nucleus 132

Aberrant regeneration of oculomotornerve 121

Acute disseminated encephalomyelitis236, 251

Adrenaline test 67Alexander’s law 34Amaurotic pupil 60Anatomy of the supranuclear

pathways 1Anophthalmos 223Aplasia 151Argyll Robertson pupil 63Astrocytomas 246

B

Bell’s palsy 149Benedict’s syndrome 119Bergmister’s papillae 152Behr syndrome 186Bielschowsky’s head tilting test 127Blepharospasm 201Botulinum toxin injection 139Brainstem syndrome 136Breughel syndrome 202

C

Calcarine sulcus 82Caloric test 43

Carotid-cavernous fistula 216Cavernoma 248Cavernous sinus syndrome 121, 126,

137Central Horner’s syndrome 67Cerebellar disorder 30Cerebellopontine angle tumor 147Chronic progressive external

ophthalmoplegia 200Ciliary ganglion 114, 115Claude’s syndrome 120Cocaine test 67Coloboma of optic disk 153Computed tomography 226

contrast medium 227principles 226

Conjugated palsies 18lesions of the basal ganglia

overactivity 22underactivity 22

lesions of the collicular area 22lesions of the frontal cortex 18

bilateral underactivity 21overactivity 18unilateral underactivity 20

Craniopharyngioma 205, 245Cuneus 83Cystic lesions 248

D

Darkness reflex 59Diplopia 126, 135Dissociated palsies 23

vertical 27Doll’s head phenomenon 50

EEnophthalmos 66Examination of a neuro-

ophthalmology case219

direct light reflex 220examination 219

Index


indirect light reflex 220near reflex 221

CNS examination 225confrontation visual

fields 221diplopia charting 222fundus examination 223Hess charting 222nystagmus 223ocular movements 221other cranial nerve

examination 224reflexes 225visual fields 223

past history 219pupil examination 220swinging flash light test 220testing of color vision 220

F

Facial anhydrosis 67Facial myokymia 203Facial nerve

course 145lesions 147nucleus 145

Foster Kennedy syndrome 192Foville’s syndrome 137Functional visual loss 211

G

Geniculate ganglionitis 148Gliomas 157

of the chiasm 242high grade 247

Gradenigo’s syndrome 137

H

Headache 206Hemifacial spasm 202Hess charting 222Heterochromia iridis 67Hippus 71Horner’s syndrome 66Hummelsheim’s operation 139Hutchinson’s pupil 65, 120Hydroxyamphetamine test 67

Hyperdeviation 126Hypoplasia 151

I

Intermediary tissue of Kuhnt 107International Headache Society 208Internuclear ophthalmoplagia 4, 23

classification 24etiology 24

Intracranial aneurysms 214Intracranial pathology 238

extra-axial tumors 240glioma 238metastasis 240

Ischemic optic neuropathy 193arteritic anterior

classic signs 193differential diagnosis 194etiology 193management 195symptoms 194

posterior 195Isolated fourth nerve palsy 126Isolated ipsilateral tear deficiency 149Isolated sixth nerve palsy 138

J

Jensen operation 139Juvenile pilocytic astrocytoma 157

K

Kearns-Sayre syndrome 200Kjer syndrome 186

L

Lateral geniculate bodies 79, 87Lesions of visual pathways 93

lateral geniculate body lesions 98optic nerve type field defect 93

arcuate nerve fiber bundle 94bitemporal hemianopia 96central bitemporal hemianopia

96junctional scotoma 96lower temoporal quantrantic

defects 98

Index 255

nasal nerve fiber bundledefects 95

papillomacular bundle 93upper temporal quadrantic

defects 97optic radiations and visual cortex

lesion 99occipital lobe lesion 100parietal lobe lesions 100temporal lobe lesions 99

Lid apraxia 203Light-near dissociation 64

M

Macular fibers 87Magnetic resonance imaging 228

claustrophobia, sedation,surveillance 232

optic pathway pathology 232restrictions 231

Malignant gliomas of the optic nerve169

clinical features 169pathology 170prognosis 170radiology 170

Marcus gunn pupil 61Meige’s syndrome 202Meningiomas 244Metastasis 247Meyer’s loop 81Micronystagmus 34Micro-ophthalmos 233Migraine 206Millard-Gubler syndrome 136Miosis 66Morning glory syndrome 155Multiple sclerosis 236, 249Myelineated nerve fibers 152Myotonic dystrophy 201

N

Nasal fibers 86Neurofibromatosis 237Non-optic reflex system disorders 30Nothnagel’s syndrome 119Nuclear fascicular syndrome 125

Nuclear third nerve paresis 118Nystagmus 32

central 51cerebellar 51deviational 36hysterical 51idiopathic congenital 52jerky 34neutral zone 34null zone 34nystagmus blockage syndrome 52ocular 35optokinetic 36-38pathological ocular

amaurotic 41amblyopic 41latent 41Miner’s 41spasmus nutans 41

pendular 33rotational 48vertical vestibular 45

canal paresis 46directional preponderance 47

vestibular 43voluntary 51

O

Ocular myastheniaclinical features 197investigations 198

electromyography 199neostigmine test 198tensilon test 198

treatment 199medical 200optical 19surgical 200

Ocular tumors 233Oculomotor (third cranial) 109

blood supply 117branches 116cavernous sinus 112ciliary ganglion 114course in superior orbital fissure 112course in the orbit 114exit from the brain 110nucleus 109


One and one-half syndrome 26Optic atrophy 185

clinical features 186differential diagnosis 187

Optic chiasma 75Optic disk pit 156Optic nerve 85, 103

blood supplyintracanalicular 107intracranial 107intraocular 108intraorbital 108

courseintracanalicular 103intracranial 103intraocular 104intraorbital 104

relationsintracanalicular 104intracranial 104intraocular 105intraorbital 104

Optic nerve gliomas 157association with neurofibromatosis

160clinical features 158histopathology 162management 167microscopic findings 164presenting signs and symptoms

159radiographic findings 161

Optic nerve head drusen 152Optic nerve hypoplasia 235Optic nerve meningiomas 170

clinical features 171histopathology 174management 178radiology 173signs and symptoms 171

Optic neuritis 187clinical features 188management 189optic neuritis treatment trial 189

Optic radiation 81, 88Optic tract 87Optokinetic nystagmus drum 36Orbital syndrome 121, 126, 138

P

Papilledema 190clinical features 190management 193

Paradoxical papillary reaction 71Paralytic pontine exotropia 26Parinaud’s syndrome 22Partial ipsilateral facial palsy 149Periventricular leukomalacia 236Petrous apex syndrome 137Pharmacology of the pupil 68Phenylephrine test 67Pilocytic astrocytoma 247Pituitary tumors 204Polycoria 72Posterior communicating artery

aneurysm 120Pseudo-Ishihara’s chart 220Pseudo-Argyll Robertson pupil 64Pseudo-Gradenigo’s syndrome 137Pseudo-ophthalmoplegia 17Psychosensory reflex 60Ptosis 66Pupil abnormalities 71Pupil cycle time 60Pupil gaze dyskinesis 121Pupillary pathways 54

accommodation reflex pathway 57convergence near reflex pathway

56papillary dilatation pathway 58pupulloconstrictor light reflex

pathway 54Pupil-sparing isolated third nerve

paresis 121Pursuit disorders 29

RRaymond’s syndrome 136Reader’s syndrome 68Retinoblastoma 233Retinochoroidal coloboma 153

SSaccadic disorders 17Secondary optic nerve tumors 179

Index 257

blood-borne metastasis 180extension from adjacent structures

181extension from the eye 179extension from the meninges and

brain 181Sellar tumors 242Septo-optic dysplasia 234Spasmus nutans 233Subarachnoid hemorrhage 214Subarachnoid space syndrome 126,

137Superior orbital fissure 112, 113, 124Supranuclear eye movement systems 2

non-optic reflex system 12position maintenance system 15pursuit system 6saccadic system 2vergence system 11

Supranuclear lesion 147Swinging flash light test 61, 220

T

Tardive dyskinesia 203Terson’s syndrome 214Third nerve fascicle syndromes 119Tic douloureux 203Tilted disk 155Tolosa-Hunt syndrome 248Tonic pupil 64Tourette’s syndrome 202Toxoplasmosis 250Trauma (nonaccidental injury) 236Trigeminal nerve

exit from the brain 140mandibular division 143maxillary division 143nucleus 140ophthalmic division 141

frontal nerve 142lacrimal nerve 142nasocilliary nerve 142

trigeminal cave 140Trochlear nerve 123

coursecavernous sinus 124exit from the brain 123

exit from the nucleus 123orbital course 124superior orbital fissure 124

lesions 125nucleus 123

U

Uncal herniation syndrome 120

V

Vergence disorders 29Vestibular system disorders 30Visual cortex 83, 88Visual pathways 73

blood supply 89lateral geniculate body 92optic chiasma 91optic nerve 90optic radiations 92optic tract 91retina 90visual cortex 92

lesions 93level 73

lateral geniculate body 79optic chiasma 75optic nerve 73optic radiations 81optic tract 77retina 73visual cortex 82

localization 84lateral geniculate body 87optic chiasma 86optic nerve 85optic radiation 88optic tract 87retina 84visual cortex 88

W

Weber’s syndrome 120Wernicke’s hemianopic pupil 63Wolfram syndrome 186

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