Nystagmus

Involuntary abnormalities of fixation

Jerk nystagmus

• Abnormal slow movement away from fixation with a fast correcting movement

Pendular nystagmus

• Abnormal slow movement away from fixation with a slow correcting movement

Oscillations

• Both the movement away from fixation and the correcting movement are fast
• Eg. square-wave jerks, ocular past-pointing, opsoclonus (saccadomania), ocular flutter
• Associated with cerebellar and brainstem disease

Direction may be

• Horizontal 
• Vertical
• Rotatory

Most forms of nystagmus are not localizable to a particular brain structure (except see-saw nystagmus).

Many forms are associated with brainstem and/or cerebellar pathology including periodic alternating, upbeat and downbeat.

Physiological

End point nystagmus: physiological fine jerk nystagmus in extremes of gazes

Optokinetic nystagmus: physiological jerk nystagmus induced by moving repetitive targets

• With targets moving left

• The left parieto-occipital-temporal cortex controls the smooth pursuit component (to the left)

• The left frontal cortex controls the saccadic movement (to the right)
• Useful in assessing
• Functional visual loss
• Homonymous hemianopia (Cogan’s law will guide where the pathology may be)

Vestibular 

• Vestibular inputs to horizontal gaze centres
• Elicited by caloric testing
• Cold water in left ear will cause right jerk nystagmus
• Warm water in left ear will cause left jerk nystagmus
• Cold water in both ears: upward jerk nystagmus
• Warm water in both ears: downward jerk nystagmus

Infantile nystagmus syndrome

Onset in infancy typically means the nystagmus does not produce oscillopsia

• Idiopathic infantile nystagmus:
• Conjugate horizontal jerk nystagmus
• Early onset (<2 months)
• Mild reduced VA, strabismus
• 40% inherited

• Slow phase velocity accelerates over time (cp with latent nystagmus)

• Infantile nystagmus with ocular/visual pathway disease (ie. sensory deprivation nystagmus):

• Erratic waveform or roving eye movements
• Reduced VA 

• Associated with cataract, albinism, cone-rod dystrophy, optic nerve hypoplasia, achromatopsia, Leber’s congenital amaurosis

• Fusion maldevelopment nystagmus (latent or manifest latent nystagmus):

• Secondary to poor fusion: no nystagmus with both eyes open, but becomes apparent on covering one eye

• Conjugate horizontal jerk nystagmus: waveform shows exponential decrease in slow phase velocity

• Fast phase is towards fixating eye
• Improves with gaze towards slow phase, worsens with gaze towards fast phase

• Head turn towards fixing eye to take advantage of null point

• Associated with infantile esotropia and dissociated vertical deviation

Congenital nystagmus mnemonic

• Convergence dampens nystagmus (nystagmus blockage syndrome with esotropia)

• In nystagmus block syndrome, the patient develops an esodeviation which aims to dampen the nystagmus and stabilise the foveal image. As the fixing eye adducts, the head turns in the opposite direction to allow fixation (which may alternate)

• Oscillopsia is absent
• Null zone 
• Gaze position does not change direction
• Equal amplitude and frequency in each eye
• Near acuity is good
• Inversion of optokinetic response
• Turning head achieves null point
• Abolished during sleep
• Latent nystagmus is present

Spasmus nutans

Rare benign idiopathic acquired nystagmus within first 2 years of life

• High frequency, small amplitude nystagmus (‘shimmering’)
• Usually horizontal and bilateral
• Head bobbing
• Torticollis

• Requires imaging to exclude intracranial lesions (midbrain pathology) and EDTs to exclude retinal dystrophy

• Typically resolves by 3-4 years old but glioma should also be considered
• Increased incidence of strabismus

Acquired conjugate

Conjugate: equal/consistent in both eyes

Associated with oscillopsia and other neurological abnormalities

Gaze-evoked nystagmus (cerebellar disease primarily, but is non-localising)

• Conjugate horizontal jerk nystagmus on eccentric gaze

• Slow-drift back to primary position then fast recovery in the direction of eccentric gaze

• Fast phase in direction of gaze

• May be due to CNS depression (fatigue, alcohol, anticonvulsants, barbiturates) or structural pathology of the brainstem/cerebellum

• Rebound nystagmus: occurs after prolonged eccentric gaze (localises to cerebellar disease)

• On returning to the primary position from eccentric gaze, there is residual tone pushing the eye eccentrically. In rebound nystagmus there is a slow deviation back in the direction of eccentric gaze and then a fast correction back to primary position.

Periodic alternating nystagmus

• Conjugate horizontal jerk nystagmus in the primary position
• Periodically changes direction
• Waxes and wanes: lasts 90s with a 10s ‘null’ period

• Typically due to vestibulocerebellar disease: oculocutaneous albinism (most common association), demyelination, Arnold-Chiari malformation, drugs (see below), may be congenital

• Patient may demonstrate alternating head turning to take advantage of shifting null position

• Can be treated with baclofen

Peripheral vestibular nystagmus

• Compare to physiological vestibular nystagmus as above
• Conjugate horizontal jerk nystagmus
• Improves with fixation
• Worsens with gaze towards fast phase or change in head position

• Destructive lesions of the vestibular system: labyrinthitis, vestibular neuritis; or irritative disease like Meniere’s

• Associated with vertigo, deafness, tinnitus

Central vestibular/cerebellar/brainstem nystagmus

• Conjugate jerk nystagmus: horizontal, vertical or torsional
• Does not change with fixation
• Horizontal
• Lesions of the vestibular nuclei or cerebellum
• Upbeat

• Cerebellar or lower brainstem (medulla) pathology: demyelination, infarction, tumour, encephalitis, Wernicke’s (thiamine deficiency)

• Downbeat: fast phase beating down

• Arnold-Chiari malformation, spinocerebellar degenerations, CVA, tumour, demyelination, drug-induced (lithium, phenytoin, carbamazepine)

Convergence-retraction nystagmus

• Can be induced by an OKN drum rotating downward: on the upward saccade, the eyes converge
• Due to co-contraction of medial recti
• Classically also shows retraction of the globe
• Associated with Parinaud’s (dorsal midbrain) syndrome

Pharmacological causes of nystagmus

• Carbamazepine
• Lithium
• Phenytoin
• Amiodarone
• Morphine
• Fomepizole
• Ketamine
• Nutmeg

## Acquired disconjugate

Unilateral or unequal between the two eyes

Acquired pendular

• May be horizontal, vertical or torsional
• Associated with brainstem and cerebellar disease including toluene abuse (paint thinner)
• Oculopalatal myoclonus
• Bilateral acquired nystagmus
• Vertical and pendular
• Associated rhythmic movements of the face, soft palate, pharynx, tongue

• Caused by brainstem stroke affecting the central tegmental tract (a triangle of circuits between the cerebellar flocculus, inferior olivary nucleus (medulla) and red nucleus (midbrain))

• Nystagmus develops months or years after the stroke

Superior oblique myokymia (a form of oscillopsia)

• Unilateral (almost always) high frequency low amplitude torsional nystagmus: may only be detectable on the slit lamp

• May cause diplopia and/or ‘jumping’ of the vision in one eye
• May be triggered by head tilt towards the affected side to stress the superior oblique

• Rarely due to underlying disease (MS and pontine tumours, or vascular compression) causing irritation of the CN IV, usually neurologically normal (idiopathic)

• Treatment
• Systemic anti-epileptics (carbamazepine, phenytoin) 
• Topical timolol
• Surgical superior oblique tenotomy

Internuclear ophthalmoplegia

• See above
• Nystagmus of the abducting eye

See-saw nystagmus

• One eye elevates and intorts, the other depresses and extorts
• Congenital form may be isolated, or related to achiasma or septo-optic dysplasia

• Acquired implies midbrain or parasellar pathology: therefore may be associated with bitemporal hemianopia due to chiasmal compression by a lesion, therefore often found alongside bilateral optic atrophy

• Pituitary adenoma
• Craniopharyngioma 

Treatment

• Difficult
• GABA-ergics eg gabapentin
• Anticholinergics eg hyoscine
• Memantine
• Optical devices 
• Surgery
• Retrobulbar botox