Nystagmus

Involuntary, rhythmic, repetitive oscillation of the eyes. Jerk nystagmus has a slow drift followed by a fast corrective phase (named for the fast phase); pendular nystagmus has equal velocity in both directions.

• Physiological: end point nystagmus, optokinetic and vestibular nystagmus during head rotation.
• Infantile (congenital) nystagmus syndrome: onset in the first 6 months, with null zone, oscillations dampened on convergence, inversion of optokinetic response. Caused by idiopathic mechanisms, albinism, achromatopsia, Leber congenital amaurosis, optic nerve hypoplasia, congenital cataract, and aniridia.
• Acquired nystagmus: peripheral vestibular (unidirectional horizontal torsional, suppressed with fixation), central (downbeat from cervicomedullary lesions such as Chiari, upbeat from medullary or midbrain lesions, see saw from parasellar lesions, periodic alternating, gaze evoked), drug induced (phenytoin, carbamazepine, lithium, alcohol, barbiturates), Wernicke, multiple sclerosis (acquired pendular), oculopalatal tremor, and spasmus nutans (nystagmus, head nodding, torticollis in infants, which needs exclusion of optic pathway glioma).
• Latent nystagmus: occurs on covering one eye, associated with infantile esotropia.

• Oscillopsia in acquired nystagmus (not present in infantile type); reduced acuity (particularly in infantile nystagmus, poor foveation); abnormal head posture to use a null point.
• Waveform helps: pendular, jerk, exponential velocity slow phase in infantile, linear slow phase in vestibular.
• Direction, gaze dependence, effect of fixation removal (Frenzel goggles) and position testing.
• Central signs: vertigo, ataxia, dysarthria, diplopia, dysmetria, skew deviation, headaches.

• Detailed history: onset, family history, medications, alcohol, vertigo, trauma.
• Visual acuity, refraction, cycloplegic refraction, slit lamp for cataract and iris transillumination (albinism), fundus (foveal hypoplasia, optic nerve hypoplasia, retinal dystrophy).
• Eye movement recording (video oculography) to define the waveform, direction and null point.
• Electroretinogram in infants with poor vision and normal looking fundi (Leber congenital amaurosis, achromatopsia, congenital stationary night blindness).
• Neurological: head impulse test, Dix-Hallpike manoeuvre, caloric testing; MRI brain with posterior fossa and craniocervical junction thin cuts for acquired central nystagmus or any neurological sign. Spasmus nutans: MRI brain and orbits.
• Genetic testing (FRMD7 for X-linked infantile nystagmus; PAX6, TYR, OCA2, GPR143 in related syndromes).
• Thiamine level or empirical treatment if alcohol or malnutrition suspected; drug levels (phenytoin, lithium).

• Treat the cause: stop offending drugs, thiamine 500 mg IV 3 times daily for 3 days in Wernicke, surgery for Chiari decompression, repair of cataract, and spectacle correction.
• Optical: correct refractive error; contact lenses often dampen infantile nystagmus better than glasses; prisms to move gaze to the null point or induce convergence (base out prism with minus lenses).
• Drug therapy:
  • Gabapentin 300 mg three times daily, titrated to 900 to 2400 mg daily, for acquired pendular and infantile nystagmus.
  • Memantine 5 mg once daily, increasing by 5 mg weekly to 10 mg twice daily (maximum 40 mg), for acquired pendular nystagmus in multiple sclerosis.
  • Baclofen 5 mg three times daily, increasing to 10 mg three times daily, for periodic alternating nystagmus.
  • 4-aminopyridine 5 mg two to three times daily (up to 10 mg three times daily) or 3,4-diaminopyridine 10 mg three times daily for downbeat nystagmus; acetazolamide 250 mg twice daily (up to 500 mg twice daily) for episodic ataxia type 2.
  • Clonazepam 0.5 mg twice daily or topical drugs (brinzolamide) in selected cases.
• Botulinum toxin to the extraocular muscles (2.5 to 5 units) when drugs fail; reserved for severe oscillopsia.
• Surgery: horizontal recession of rectus muscles with tenotomy and reattachment, or Anderson-Kestenbaum procedure (recession and resection of horizontal muscles to move the null zone to primary position), mainly for abnormal head posture in infantile nystagmus.
• Low vision aids, driving counselling and education support. Children need amblyopia assessment and patching only when strabismic amblyopia is present.