applied anatomy of visual pathway
TRANSCRIPT
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SEMINAR
APPLIED ANATOMY OF VISUAL PATHWAY
MOERATOR-Dr. SUJATA LAKHTAKIA
Dr. SYED IMRAN
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INTRODUCTION
The afferent visual pathway which is responsible for mapping the external world into our consciousness begins with the anterior segment and via the retina, optic nerve, optic chiasm, optic radiations end in the visual cortex.
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INTRODUCTION
Components of afferent visual pathway : Retina - Rods and Cones
Bipolar cells Ganglions cells Optic nerve (Ganglion cell axons) Optic chiasm Optic tracts Lateral geniculate body Optic radiations Visual cortex
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INTRODUCTION
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OPTIC NERVE The optic nerve is formed by the axons of the
ganglion cells .
It represents the second order neurons of the visual pathway.
80% of the fibers originate from the macular region which represents 90% of retinal ganglion cells.
There are 2.2 to 2.4 million fibers in the two optic nerves representing 42% of all fibers entering and leaving the cns.
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OPTIC NERVE
The optic nerve is not really a nerve .it is actually a tract ( a part of cns).
Its axons are myelinated by oligodendrocytes and not schwan cells.
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OPTIC NERVE
Humans have two types of retinal ganglion cell system. P cell system M cell system
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OPTIC NERVE
P cell system : 90% of ganglion cellsSmall cells (small receptive fields)Small caliber axons (slow conduction)
Concentrated in macula Project in parvocellular
layer of LGN(3,4,5,6) Mediate spatial resolution and color perception
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OPTIC NERVE
M cell system 10% of ganglion cellsLarge cells (large receptive field)Large caliber axons (fast conduction)
Concentrated in perepheral retina Project in magnocellular layers of LGN (1,2) Mediate motion detection
This explains in part the high sensitivity we have for light and motion detection (fast transmition) while color detection is slow.
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OPTIC NERVE
Koniocellular pathway : Smallest ganglion cells (W cells in cat)
Very large receptive fieldsTerminate in the interlaminar
zone and superfical layer of LGN Functions not known
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OPTIC NERVE
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OPTIC NERVE
Divisions of optic nerve
Intraocular portion (in the globe)
Intraorbital portion ( in the muscle cone)Intracanalicular
portion ( in the optic canal)Intracranial portion
(in the cranial cavity)
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OPTIC NERVE
Dimensions of optic nerve (in mm)
SEGMENT LENGTH DIAMETER
Intraocular 1.0 1.5 to 1.75
Intraorbital 25 3 to 4
Intracanalicular 4 to 10 3 to 4
Intracranial 10 4 to 7
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OPTIC NERVE Intraocular portion
It is the shortest portion (1mm)
It extends from superficial nerve layer to the posterior margin of sclera
The nerve fibers are non myelinated
It can be divided into Superficial nerve fiber layerPre laminar region Laminar region
Retrolaminar region
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OPTIC NERVE Superficial nerve fiber layer
It is made up of axons of ganglion cells
Nasal fibers
Temporal fibers
Papillomacular bundle
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NERVE FIBRE LAYER ANALYSIS
Technique : Fundus examination(Green light) Confocal scanning technique OCT Scanning laser polarimetry
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OPTIC NERVE
Prelaminar portion It extends from the surface of the optic disc
to the posterior margin of the choroid.
It can be further divided into -Pars retinalis -Pars choroidalis
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OPTIC NERVE
Optic disc or Optic nerve head:
The optic nerve head is a 'plug-hole' down which over 1 million nerve fibers descend through a sieve-like sheath known as the lamina cribrosa
It is -Oval -Horizontally1.5mm -Vertically 1.75
mm
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OPTIC NERVE
Arrangement of nerve fibers within the optic nerve head:
Peripheral retinal fibers – superficial
Central retinal fibers –deep
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OPTIC NERVE
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OPTIC NERVE Laminar portion (pars scleralis)
It is enclosed in the scleral canal Scleral canal is 0.5mm long
Lamina cribrosa It is a sieve like connective tissue
meshwork integrated with the scleraIt has 10 connective
tissue plates with 200 to 300 pores They transmit
axonal bundles
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OPTIC NERVE
Retrolaminar portion Just posterior to pars scleralis
Fibers get myelinated by oligodendrocytes causing a doubling of the thickness of the nerve to 3mm
Nerve gets surrounded by menengial sheaths
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OPTIC NERVE
Intra orbital portion It extends from the back of the eye to the optic canal
It runs backwards and medially
25 to 30 mm long 3 to 4 mm thick
This length is far more than the distance between the back of globe and optic canal which is 18mm
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OPTIC NERVE
For this reason the nerve is slack or S shaped in primary position
It allows eye movements without stretching
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OPTIC NERVE
Annulus of zinn It is a tough fibrous sheath Located at the orbital apexGives origin to the four recti
Because superior and medial recti partly originate from the nerve sheath itself inflammatory optic neuropathy may be associated with pain on ocular movements
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OPTIC NERVE
Intracanalicular portionOptic canal is -8 to 10 mm long
-5 to 7 mm wide It runs superiorly and
medially The optic nerve
passes through the canal accompanied by opthalmic artery (inferiorly ) and sympathetic nerves
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OPTIC NERVE
The nerve inside the canal is immobile and fixed
This makes it highly vulnerable to injury by blunt trauma
Optic nerve edema in this area can produce compartment syndrome further causing nerve damage
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OPTIC NERVE
Intracranial portion Its length varies from 5 to 16 mm Average 10mm Diameter 4.5mmIt is not covered by menenges It is related bellow and temporally to the
anterior loop of internal carotid artery
The anterior cerebral artery crosses over the nerve
It terminates in the chiasm
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OPTIC NERVE
At its intracranial exit the optic nerve passes under a fold of dura ( Falciform ligament ) that may impinge on the nerve, especially if it is elevated by lesion of sphenoid or sella.
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OPTIC CHIASM
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OPTIC CHIASM
It is a junction at which the two optic nerves join to allow hemidecussation of nasal fibers to opposite optic tracts and the direct passage of temporal fibers to the ipsilateral optic tracts.
Thus, all visual information from the right visual space is transmitted to left cerebral cortex and vice versa.
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OPTIC CHIASM It is 12 х 8 х 4mm in size
Situated 10mm above the pituitary and seperated from it by the suprasellar cistern
It is related-- laterally to the supraclinoid segment of carotid arteries
-- inferolaterally to the cavernouss sinuses
It has an inclination of 45˚to the horizontal
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OPTIC CHIASM
1.Optic nerve 2.Optic chiasma 3.Optic tract 4.Tuber cinereum 5.Mamillary bodies 6.Anterior perforated substance 7.Olfactory trigone 8.Pons 9.Uncus
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Upper nasal fibers
Macular fibers
Lower nasal
Anterior clenoid
Pituitary
Third ventricle
Craniopharangioma
Chiasm
Posterior clenoid
Dorsum sellae
Diphragma sellae
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OPTIC CHIASM Chiasmal nerve pathways
Lower nasal :Pass low and anterior More vulnerable to damage by pituitary lesion
Wilibrands knee : Some inferonasal fibers loop forwards into the contralateral optic nerve
It may be affected in lesions of the terminal part of optic nerve
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OPTIC CHIASM
Upper nasal : Pass high and posteriorlly They are involved in lesions above the chiasm
Macular fibers : decussate throughout the chiasm
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LESIONS OF OPTIC CHIASM Anterior Chiasmal Lesions
Damage to ipsilateral optic nerve and Knee of Wilibrand
RE LE
Rt Anterior Chiasmal lesion
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LE RE
HM
CF
Decussating fibersare most vulnerable
VISUAL FIELD DEFECTS IN PITUITARY ADENOMAS
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VISUAL FIELD CHANGES IN CRANIOPHARANGIOMA
LE RE
HM
CF
Posterior crossing fibers most vulnerable
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Meningioma LE RE
Junctional scotoma
Tuberculum Sellameningioma
Olfactory groove meningioma
Sphenoid ridge meningioma
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OPTIC CHIASM
Anatomical variations : Variations in the length of optic nerve alters the relative position of the chiasm to the sellar structures
Central –80%
Prefixed--10%
Postfixed –10%
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CENTRAL 80%
PREFIXED 10% POSTFIXED 10%
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OPTIC TRACTS
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OPTIC TRACTS
Each optic tract contains ipsilateral temporal and contralateral nasal fibers
They wind round the cerebral peduncle of the rostral midbrain and each divide into
Lateral root
Medial root
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OPTIC TRACTS
Lateral root :Large ( 90%)
Concerned with conscious visual functions
Terminates in Lateral geniculate body
Medial root :Small ( 10%)
Not concerned with conscious visual functions
Contains six groups of fibers
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OPTIC TRACTS
Termination of medial root fibers : -Superior Colliculus -three groups Visual grasp reflex Automatic scanning of images
Visual association pathways -Pretectal nucleus
Pupilary light reflex
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OPTIC TRACTS
-Parvocellular reticular formation Arousal function in response to light
-Suprachiasmatic nucleus of hypothalamus It is called Retinoypothalamic tract
Photoperiod regulation Beneficial effect of sunshine on mood
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OPTIC TRACTS
Arrangement of Fibers : Fibers from superior retina remain
superiorly while those from inferior remain inferiorly Fibers from corresponding parts of the retina do not pair This explains the incongruous nature of visual field defects seen in optic tract lesions Magnocellular axons dominate the periphery while Parvocellular dominate the center
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OPTIC TRACTS
As temporal visual is 1.5 times the size of nasal field
The contralateral nasal retina supplies more axons (55% ) than the temporal retina of ipsilateral (45% ) eye
This is the reason for monocular temporal
crescent ( 60 to 90˚) in contralateral visual field caused by damage to the most anteromedial part of occipital cortex
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OPTIC TRACTS
Lesions of optic tract cause incongruous homonymous hemianopia contralateral to the affected optic tract
RE LE
Rt Optic tract lesion
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LATERAL GENICULATE NUCLEUS
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LATERAL GENICULATE NUCLEUS
It is a synaptic zone (relay center ) for higher visual projections
Located in the posteroinferior part of thalamus
It is divided into six layers by medulated nerve fibers
Numbered 1 to 6 from below upwards
Arranged in a dome shaped pattern
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In the early 1960s, David Hubel and Torsten Wiesel (who won the Nobel Prize for Medicine in 1981) were the first to use microelectrodes to explore the receptive fields of the neurons in the lateral geniculate nucleus and the visual cortex
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LATERAL GENICULATE NUCLEUS
Magnocellular fibers layer 1,2 Parvocellular fibers layer 3,4,5,6 Koniocellular fibers interlaminar zone
superficial layers Contralateral axons layer1,4,6 Ipsilateral axons layer 2,3,5
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LATERAL GENICULATE NUCLEUS
In LGN the retinal representation rotates to almost 90˚
Superior fibers move superomediallyInferior fibers move inferolaterally Macular fibers move superolaterally
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LATERAL GENICULATE NUCLEUS
The LGN also receives inputs from cortex, reticular formation, occulomotar center, superior colliculus and pretectal nucleus
The visual impulses are modified in accordance to the impulses from these centers and relayed to the visual cortex
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LATERAL GENICULATE NUCLEUS
Lesions of Lateral geniculate nucleus cause incongruous homonymous hemianopia contralateral to the to the affected optic tract
RE LE
Rt Optic tract lesion
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OPTIC RADIATION
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OPTIC RADIATIONS
Also called Geniculocalcarine tracts
These consists of nerve fiber bundles whose cell bodies lie in the LGN
They terminate in the visual cortex
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OPTIC RADIATIONS
Along the radiations the fibers from corresponding retinal elements lie progressively closer together
This is the reason why lesions in posterior radiations cause more congruous hemianopia than anterior
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LGN
Inferior fibers
Myers loop
Superior fibers
Lateral ventricle(Posterior cornu )
Visual cortex
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LESIONS OF OPTIC RADIATIONS
Temporal Lobe (Myers loop) : Conralateral superior wedge shaped incongruous homonymous
hemianopia (Pie in the sky defect ) sparing the central vision
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LESIONS OF OPTIC RADIATIONS
Parietal lobe : Conralateral inferior wedge shaped incongruous homonymous
hemianopia sparing the central vision
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LESIONS OF OPTIC RADIATIONS
Main radiations : Complete homonymous hemianopia on
contralateral side
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VISUAL CORTEX
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VISUAL CORTEX
It can be divided into 1.Primary visual area ( V1, Area 17, striate cortex )
2. Secondary visual areas -Area V2 ( Area 18 , Parastriate cortex) -Area 19 (Peristriate cortex) -Area V3a and Area V3 -Area V4 -Area V5 ( MT ) -Area V6
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VISUAL CORTEX
To date, researchers have discovered nearly 30 different cortical areas that contribute to visual perception
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VISUAL CORTEX
Primary visual cortex ( Area 17 ) -Also called striate cortex because of
prominent white bands of fibers –the stria of Gennari
-Located within the depths of calcarine sulcus
-Envelops the posterior pole upto 1.5 cm
- Measures 20 to 45 sqcm
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VISUAL CORTEX
Projection of fibers -Superior retinal Upper lip of calcarine
quadrants sulcus
-Inferior retinal Lower lip of calcarine quadrants sulcus
-Macular fibers Posterior most portion of cortex
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VISUAL CORTEX 50 to 60 % of visual cortex responds to central
10˚of retina and 80% of the cortex to central 30˚ of retina
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VISUAL CORTEXHitologically it has 4 different layers Layer 4 is most cellular Called the internal granular layer Optic radiations mainly terminate this layer The predominant cell type not being pyramidal but
small stelate It is further subdivided into 4a,4b and 4cMagnocellular inputs 4c alphaParvocellular inputs 4c beta
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VISUAL CORTEX
The cells of Lamina 2,3 Secondary
visual cortex
Lamina 5 Superior
colliculus Lamina 6 LGN
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VISUAL CORTEX
Secondary visual areas : Nonstriate cortex They are Visual association areas
They lie above and bellow the Area 17 and extend into the lateral surfaces of the cortex
They show the usual six layers but layer 4 is less extensive
They receive inputs from area 17, thalamus, basal ganglia, and other areas of cortex
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VISUAL CORTEX
There connections mainly fallow Dorsal and Ventral pathways
Dorsal outputs (Magnocellular ) V5 in parietal cortex Stereopsis and movement detection
Ventral output (Parvocellular ) to V4 in inferotemporal cortex
Analysis of color and form
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VISUAL CORTEX
Area V2 : Parastriate cortex or Area 18Located adjacent to Area 17
Connected to V1, V3 of same side and V1 and V2 of opposite
Also connects to other areas of cortex and mid brain
It is a site of integration of information
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VISUAL CORTEX
Area V3 andV3a : In lunate and parietooccipital sulciThey are sensitive to motion and
direction Area V4 :
Located in lingual and fusciform gyrus Sensitive to color
Area V5 : Located anterior and lateral to area V4Highly sensitive to speed and direction
of moving stimulus
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LESIONS OF OPTIC RADIATIONS AND VISUAL CORTEX
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Anterior visual cortex dysfunction Caused by PCA occlusion
Contralateral Congruous homonymous hemianopia With Macular sparing
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Macular Cortex lesion Severe hypotension Contralateral Homonymous
hemianopia involving only the Fixation region
Contralateral Monocular temporal crescent is seen in lesions of the most anteromedial part of the visual cortex
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BLOOD SUPPLY
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BLOOD SUPPLY The blood supply of optic nerve varies from
segment to segment
The central retinal artery :Branch of ophtalmic artery It enters the optic nerve 10-12mm
behind the globeIt divides into superior and inferior
arcades
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BLOOD SUPPLY Intraocular Optic nerve
Nerve fiber layer Central retinal artery
Prelaminar Nerve Short post ciliary Recurrent choroidal
arteries Laminar Nerve Short post cillary arteries
Branches from circle of Haller and Zinn Retrolaminar Nerve Pial
Short post cillary arteries
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BLOOD SUPPLY
Intraorbital Part : Proximally Pial vascular network
Branches of Opthalmic artery
Distally Intraneural branches of CRA
Most anteriorly Post cillary arteries
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BLOOD SUPPLY Intracanalicular part Opthalmic artery
Intracranial part Internal carotid arter Opthalmic artery
OPTIC CHIASM Sup hypophysial artery Internal carotid artery
Post communicating artery Ant cerebral artery Ant communicating artery
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BLOOD SUPPLY
OPTIC TRACT Ant chorotdal artery (br of ICA)
LATERAL GENACULATE NUCLEUS Ant choroidal artery Posterolateral choroidal
artery ( br of PCA)
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BLOOD SUPPLY
OPTIC RADIATIONSCommencement Ant choroidal
arteries Posterior fibers Lateral striate (deep optic) branches of PCA
VISUAL CORTEX Penetrating branches of Cortical arteries
mainly Calcarine and parieto-occipital branches of PCA
Anastamosis between MCA and calcarine artery
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REFERENCES
• Ophthalmology, 2nd edition : Yanoff & Duker• Clinical Neuroophthalmology :Walsh & Hoyt΄s• American academy of ophthalmology :Basic and
clinical science course• Clinical Ophthalmology : Kanski• Parson’s basic diseases of the eye : Radhika
Tandon, Ramanjeet Sihota ; 20th edition• Clinical Ophthalmology : A.K. Khurana ; 3rd
edition• Anatomy and Physiology of Eye: A.K. Khurana 2nd
ed.
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Thank You…
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DEVELOPMENT OF OPTIC NERVE
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DEVELOPMENT OF OPTIC NERVE It develops from the optic stalk that connects the
optic vesicle and fore brain The optic stalk is Fluid
filled tube Lined by Neuroectoderm
It has two separate regions Distal crescent shaped invaginated segment
(choroidal fissure)Proximal non invaginated circular
segment
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DEVELOPMENT OF OPTIC NERVE
At the 6th week (17mm stage) nerve fibers begin to grow and the embryonic cleft begins to close
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DEVELOPMENT OF OPTIC NERVE
This results in a double layer of neuroectoderm with obliteration of the fluid filled cavity
The invagination process leads to incorporation of hyaloid vessels and surrounding mesenchyme
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DEVELOPMENT OF OPTIC NERVE
The ganglion cell axons run through the inner neuroectodermal layer towards the brain
At about the end of 6th week, optic nerve fibers penetrate the under surface of forebrain, in 7th week optic chiasm is formed, and at 9thweek optic tracts are formed.
The outer neuroectodermal layer differentiate into peripheral glial mantle and glial components of lamina cribrosa
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DEVELOPMENT OF OPTIC NERVE
Initially there is increase in the number of axons10 to 12 wks – 1.9 million
16th wk - 3.7 million
Later attrition of axons occur 33rd wk - 1.1 million
Myelination Begins in the LGN – 5th month of gestation Reaches Chiasm - 6 to 7th month of gestationLamina cribrosa – Term
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APPLIED ANATOMY
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CONGENITAL ANOMALIES
Prepapillary loop : vascular loop extending from the disc margin into vitreous cavity
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CONGENITAL ANOMALIES
Bergmeister papilla : This cone shaped mass of tissue derived
from the retinal cells is present at the presumptive optic disc during fetal life
It involutes during development The degree of atrophy
determines the depth of physiological cup -Complete atrophy –
Deep cup -Moderate atrophy –Shallow cup -Minimal atrophy --Substantial glial elements present on cup called persistent Bergmeister papilla
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CONGENITAL ANOMALIES
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CONGENITAL ANOMALIES
Medulated nerve fibersSeen in 0.3 to 0.6 % population
Whitish patch with feathery margins usually adjoining the disc margins
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CONGENITAL ANOMALIES
Tilted disc :This occurs due to oblique entry of
optic nerve into the globe
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CONGENITAL ANOMALIES Optic disc pits :
Herniation of dysplastic retina into the nerve substance
Round to oval grey white depression in the disc usually temporally
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CONGENITAL ANOMALIES Optic nerve hypoplegia
Decreased number of axons with normal mesodermal components Small pale disc with surrounding double ring sign
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CONGENITAL ANOMALIES
Megalopapilla : Large optic disc (>2mm)with large CD ratio
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CONGENITAL ANOMALIES
Optic disc Coloboma : An inferior segmental form of optic nerve hypoplasia.
Disc appears enlarged with a sharply demarcated glistening white bowl shaped excavation.
Inferior rim thinner ; only remaining neural tissue lies superiorly in a C shaped / Moon shaped crescent. neural tissue lies superiorly in a C shaped / Moon shaped crescent
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OPTIC DISC DRUSENS
BURRIED EXPOSED
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CONGENITAL ANOMALIES
MORNING GLORY SYNDROME – this is unilateral congenital anomaly, with enlarged and excavated disc with annular pigmented retinal tissue around it.
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PAPILLEDEMA
Optic disc edema, usually bilateral resulting from raised ICP.
Purely hydrostatic, non-inflammatory phenomenon,
Pathophysiology; blockage of axoplasmic transport along with edema and vascular congestion.
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EARLY
CHRONIC
FULLY DEVELOPED
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OPTIC NEURITIS Optic neuritis: Inflammatory, infective or
demyelinating process affecting the optic nerve.
Classified as PapillitsNeuroretinitis Retrobulbar neuritis
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PAPILLITIS NEURO RETINITIS
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OPTIC ATROPHY
Condition of the disc following degeneration of the optic nerve.
Primary Optic Atrophy:
Lesions affecting the visual pathway from the retrolaminar portion of the optic nerve to the LGB.
No ophthalmoscopic evidences of previous local inflammation
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OPTIC ATROPHY
Secondary or Postneuritic optic atrophy:Follows an injury or direct pressure
affecting the visual nerve fibers in any part from lamina cribrosa to LGB, preceded by swelling of optic nerve head.
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PRMARY
Pale Flat discDistinct margins
POSTNEURITIC
Dirty grey disc Indistinct margins
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REFERENCES
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OPTIC NERVE
Meningial sheaths are supplied by sensory nerves, which account
in part for the pain experienced by patients
with inflammatory optic nerve diseases
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OPTIC NERVE
Microglia
They are immune derived cells
Protect the optic nerve from infections
Apoptosis of ganglion cells which occur in various diseases and during development is modulated by these cells
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OPTIC NERVE
Oligodendrocytes These are specialized glial cells
Provide myelination to axons
In up to 0.6% myelination may extend to the peripapillary retinal nerve fiber layer
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OPTIC NERVE
Meningial sheaths Pia materArachnoid materDura mater
Pia materIt is the inner most layer
It sends numerous septa into the nerve dividing the nerve axons into bundles
These septa continue throughout the nerve and end just before the chiasm
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OPTIC NERVE
Dura mater Anteriorly it fuses to the outer layer of sclera
Posteriorly it splits at the orbital opening, majority continuing around the optic nerve and a thin portion blending with the periostium around the optic canal
This completely immobilizes the nerve Blunt trauma to brow area may transmit forces
to this area causing tear between dural sheath and its attachment .This leads to interruption of blood vessels and severe nerve damage
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OPTIC NERVE Arachnoid mater It is connected to the pia across the
subarachnoid space by vascular trabeculae
The subarachnoid space ends anteriorly at the lamina cribrosa and posteriorly it is continious with the subarachnoid space of the brain
The central retinal vessels cross the subarachnoid space and are therefore vulnerable particularly the vein in case
of raised ICT
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OPTIC NERVE
Astrocytes These are specialized glial cells They have extensive neurofibrilary processes spread among nerve fibers Functions :
Formation Forms blood brain barrier Provide nutrition and support to axons
When axons are lost they proliferate and fill the empty space