Nystagmus

a rhythmic oscillation of the eyes. It has many different patterns, and may be physiological or pathological

Physiological Nystagmus

not due to a disease process Has no benefit, except as a diagnostic tool End point nystagmus Postrotational nystagmus Induced caloric testing Optokinetic nystagmus Voluntary nystagmus

Pathological nystagmus

Classification

When describing the nature of nystagmus, the following terms should be used:» Congenital/acquired» Jerk/Pendular» Direction of fast phase» Frequency» Amplitude» Grading system for gaze

Pendular Nystagmus:

Usually congenital, or onset in early childhood,

due to low vision Both phases have similar speed.

Jerk Nystagmus:

can be congenital or acquired. Vision is reduced by varying degree (unpredictable),

but is the result rather than the cause of the nystagmus Wave form: slow movement (pursuit) in one direction

(the defect) fast movement (saccade) in other direction (the

correction).

Grading System: eg for right beating nystagmus

Grade 1 = present in right gaze only Grade 2 = present in right gaze and primary

position Grade 3 = present even in left gaze

CONGENITAL NYSTAGMUS

due to a congenital anomaly of the motor system or to a congenital disorder of vision.

may appear during early childhood but is rarely present at birth.

Low Vision Nystagmus (syn. Pendular nystagmus)

Characterised by slow pendular oscillations generally the wave form is very variable. Established pendular nystagmus (by about 6 months in congenital visual deprivation) has a

poor visual prognosis. Rarely ever better than 6/36. Causes:

» Failure of the fixation reflexes during the critical period (first 3 months) due to

» eg bilateral corneal scarring, infantile glaucoma, dense cataracts, ocular albinism, optic nerve hypoplasia, optic atrophy, macular hypoplasia, rod monochromatism, Leber’s amourosis.

Nystagmus with relatively normal vision

Congenital idiopathic jerk nystagmus all types of manifest nystagmus without a

primary visual defect, either present at birth or developing during the first few weeks of life as the visual fixation reflexes develop

Bilateral nystagmus Eyes otherwise healthy Predominantly in one plane, usually horizontal May start as pendular, but becomes jerky with fast phase to

right on right gaze and left on left gaze. Null zone somewhere in between, where acuity usually

quite good. Vision often improves on convergence Intensity of the nystagmus increases on attempting fixation

May have a superimposed latent component Reduced lid closure Oscillopsia is rare Often face turn, voluntary convergence or head shaking or

nodding to minimise nystagmus Commonly hereditary (irregular X-linked dominant) Precise mechanism unknown

Management :

treatment rarely required, unless an extreme AHP is adopted to achieve maximum VA, when prisms or surgery to centralise the null point can be tried.

Occasionally base-out prism to induce convergence

Latent and Manifest Latent Nystagmus

Horizontal jerk nystagmus presents when the light stimulus is reduced to either eye (eg by occluding).

In latent, no observable movement is present on uncovering and full BSV is restored.

In manifest latent nystagmus the nystagmus has a reduced amplitude but remains when both eyes are open.

ACQUIRED NYSTAGMUS

Occurs in many CNS disorders, especially those involving the cerebellum, brainstem and vestibular mechanism.

More common in adults» labyrithitis, » central vestibular disease/tumour, » cerebellar damage» gaze evoked nystagmus» convergence retraction nystagmus (Parinaud,s syndrome)

» INO

Nystagmus

The presence of nystagmus should be treated as a sign, rather than a diagnosis and there is great variation and variability in its appearance

However there are characteristics of the different types which can aid diagnosis, whilst not being conclusive eg direction, speed and persistence.

Nystagmus may be the first sign of a serious neurological defect, and this should always be considered.

Two acquired conditions occurring in childhood are as follows:

Spasmus Nutans See-Saw nystagmus

Spasmus Nutans Nystagmus, involuntary head movements, AHP Onset 3-18 months of age Fine rapid eye movements; jerky, small amplitude, high

frequency Horizontal, vertical or rotary, or a combination of these Considerable variation in nystagmus in different positions

of gaze Involuntary head movements comprising nodding or

shaking, or a combination of both; variable.

Spasmus Nutans These do not appear to compensate for eye movement as

they are of different frequency Most cases resolve spontaneously by age 3 years. Benign, but can be associated with CNS disease, therefore

should be investigated.

See-Saw nystagmus

Usually an acquired motility disorder associated with chiasmal lesions

where one eye elevates and intorts followed by depression and extorsion of the other eye

Rare

Clinical procedure for nystagmus cases

Close questioning as to the onset of the nystagmus, family history, general health, medication, history of CNS disorders, associated symptoms (oscillopsia, vertigo, unsteadiness and loss of vision all imply acquired forms)

Carefully note the type of nystagmus, distance/near, latency, AHP etc VA recorded uni- and binocularly, with and without AHP, dist and

near and compared Full ophthalmoscopic, slit-lamp (transillumination), and binocular

vision assessment

Unless 100% sure the nystagmus is congenital or longstanding, refer for further investigation.

Neurological causes are rare, but serious and diagnosis of congenital nystagmus should only be made by exclusion of other causes.

electro-diagnosis is very valuable as Lebers amaurosis or rod monochromatism cannot be detected ophthalmoscopically.

SUPRANUCLEAR GAZE CONTROL

Signals which control ocular movement are initiated in the cerebral hemispheres.

They are then transmitted to the gaze centres and oculomotor nuclei in the midbrain and pons, and leave the brain in the 3rd, 4th and 6th cranial nerves

Supranuclear neuronal pathways: conduct impulses from cerebral hemispheres to gaze centres

Internuclear pathways: conduct impulses from gaze centres to ocular motor nucleii

Infranuclear pathways: 3rd, 4th and 6th cranial nerves There are three forms of conjugate eye movement (ie as a yoked pair), and

each has a different control centre.

Saccades =contralateral frontal pre-motor area Pursuit= ipsilateral occipito-parietal area Vestibular reflexes= vestibular nuclei in the pons

Conjugate eye movementControl centre

These impulses are transmitted to the gaze centres, which mediate the conjugate eye movement.

Horizontal and vertical gaze control are quite separate, and therefore should be investigated separately.

The horizontal gaze centre is in the pons at the level of the 6th nerve nucleus. Horizontal movement to the left is controlled by the left horizontal gaze

centre, and vice-versa for theright.

The vertical gaze centre is in the midbrain but not much is known about vertical gaze control.

Gaze Palsies

An inability to make a conjugate ocular movement in one direction.

This does not cause diplopia since the visual axes remain parallel.

By investigating each reflex and conjugate movement in turn, it is possible to establish where a lesion exists

GAZE PALSIES Examples

supranuclear lesions do not affect vestibular reflexes, so these remain intact (test by calorics or dolls head reflex)

frontal lesions cause unilateral saccadic palsies occipital lesions cause unilateral pursuit palsies pontine lesions affect horizontal gaze but not vertical upper midbrain lesions affect vertical gaze Horizontal saccadic gaze palsies are most common

Parinauds Syndrome

Vertical gaze palsies usually form part of a triad of signs, which is known as Parinauds syndrome.

This is relatively rare and is caused by lesions in the upper midbrain.

The signs are» vertical gaze palsy (saccadic upgaze affected first» loss of light reflex (near reflex intact)» convergence retraction nystagmus

Parinauds Syndrome

The convergence retraction nystagmus is seen spontaneously or (more usually) on attempted upgaze.

The lesion is thought to cause disinhibition of the ocular motor nuclei allowing bursts of co-firing of the extra-ocular muscles.

As the MR is the most powerful muscle this results in convergence and a retraction of the globe

Causes:» Tumours of the pineal gland *(most common)» Atherosclerosis» Embolism, Vasculitis

Internuclear Ophthalmoplegia Caused by lesions in the medial longitudinal fasciculus (MLF),

the area carrying internuclear neurones between 6th and 3rd nerves. Type depends on the precise location of the lesion in MLF. It can be unilateral or bilateral: Unilateral: interneurones from one 6th nerve nucleus affected,

causing loss of adduction of the affected MR on attempted conjugate gaze.

Saccadic, pursuit and vestibular systems are all affected. Also get abducting nystagmus of the other eye (reason for this is

not clear) Convergence can remain intact

Internuclear Ophthalmoplegia

Bilateral:interneurones from both 6th nerve nuclei affected. Often assymetric.

Patients rarely complain of diplopia Cause; MS is the commonest cause of unilateral (&often bilateral)

INO in the younger patient (may be the presenting feature) In the older patient, small blood vessel occlusion is likely in

unilateral INO, and tumour is a possibility in bilateral Most spontaneously recover, except if tumour.

Paralytic Pontine Exotropia (The “One and a half” syndrome)

Lesion affecting both the horizontal gaze centre and the adjacent MLF = gaze palsy + INO.

The only remaining horizontal movement is abduction of the unaffected LR with abducting nystagmus ie gaze palsy to one side, INO to the other.

Complete “one and a half” syndromes are uncommon, but partial is more common.

Cause : tumour is likely.

Pseudostrabismus

Epicanthus in infants can be more or less pronounced. Epicanthus can obscure the inner canthus giving rise to the

appearance of esotropia when none is present. In time epicanthal fold usually disappears with the

development of the bridge of the nose Other examples of pseudostrabismus include

» facial asymmetry» failure of the optical (centres of the cornea and lens) and

visual axis (fovea to fixation point) to coincide