Nystagmus

Educational Objectives

The goal of this program is to improve the diagnosis and treatment of balance disorders. After hearing and assimilating this program, the clinician will be better able to:

1. Characterize, describe, and classify various patterns of nystagmus.

2. Explain various forms of treatment available for nystagmus.

Summary

Definition: involuntary rapid rhythmic oscillatory eye movements with at least 1 slow phase; distinguish jerk nystagmus, which has slow and rapid phase as in vestibular nystagmus, from pendular nystagmus, which has only slow phases; differentiate from saccadic intrusions or oscillations such as square wave jerks or ocular flutters on examination; other conditions such as opsoclonus lack slow phase movements (saccade generated)

Terminology: direction — choose reference frame in description of eye movements such as eye, head, or gravity coordinates; torsion — common source of miscommunication; clockwise or counterclockwise should specify patient’s vantage point and refer to quick phase; binocularity — most vestibular nystagmus binocular; bilateral or unilateral refers more to direction, ie, present to right, present to left; conjugacy — both eyes rotating together in same direction by same amount (most vestibular nystagmus); may be disconjugate either because dissociated (amplitude different in each eye) or disjunctive (direction different between eyes); waveform — pendular, horizontal, vertical, purely torsional, mixture, elliptical or circular if perfectly out of phase; pendular nystagmus commonly visually disabling, as eye continuously moving; waveform described as constant velocity (eg sawtooth, accelerating or decelerating; velocity — slow-phase velocity most useful quantifier of intensity, although difficult to estimate at bedside; use of frequency helpful, mainly with low-frequency nystagmus (1 or 2 Hz); amplitude — distance from start to end of slow or quick phase; by itself provides little useful information; intensity — qualitative gauge of product of frequency and amplitude, rough estimate of velocity

Other characteristics: continuous, paroxysmal, or continuous but varying in direction or amplitude; useful to observe nystagmus in different gaze positions, including 9 cardinal directions; effects of visual fixation — observe during binocular and monocular vision; induce monocular gaze with Frenzel lenses, video oculography, covering or shining bright light in 1 eye

Saccadic intrusions: square wave jerks — small movements that bring eye away from target and back with small intersaccadic interval; usually asymptomatic but in cerebellar disease may have larger macrosaccadic oscillations; ocular flutter or opsoclonus — horizontal or multidirectional back-to-back saccades; voluntary saccadic oscillations, voluntary nystagmus or functional saccadic intrusions — ranges from “party trick” in some subjects who can induce nystagmus with convergence to more diagnostically challenging patients with functional disorder

Nystagmus-like movements: spasmus nutans — brief shimmering eye movements associated with head movement in infants; usually disappears over time; superior oblique myokymia — monocular condition involving brief paroxysms of torsional shimmering eye movement related to brief contraction of superior oblique muscle, often due to something extrinsic (eg, blood vessel compressing trochlear nerve); ping-pong gaze — slow back-and-forth eye movements seen in coma patients

Physiologic forms: may see tiny amount of end-point nystagmus with extreme gaze; often challenging to differentiate from pathologic gaze-evoked nystagmus; optokinetic, optokinetic after-nystagmus, per- or postrotational nystagmus may all be elicited in otherwise healthy patients in laboratory

Pathologic nystagmus: speaker classifies as spontaneous, gaze-evoked, or elicited by provocative maneuvers

Spontaneous nystagmus: many forms; present with head stationary, and patient sitting upright with eyes straight ahead; challenge involves differentiating spontaneous vestibular nystagmus from forms of central origin; spontaneous peripheral-type vestibular nystagmus most common, but lesions within vestibular nuclei in brainstem can cause similar-appearing nystagmus; definition — spontaneous vestibular nystagmus defined as spontaneous jerk nystagmus believed due to imbalance in vestibular tone; peripheral vestibular nystagmus normally binocular, conjugate, moves in same head-referenced coordinates regardless of direction of gaze (consistent with dysfunction in ≥1 semicircular canals); always beats in same plane and direction (obeys Alexander law); suppressed by visual fixation; if measured, has constant-velocity slow phases

Central vs peripheral patterns: stimulation of individual semicircular canals elicits different patterns of slow-phase eye movements; summation yields mixed horizontal torsional nystagmus, denoting peripheral pattern; purely downbeat, upbeat, or torsional nystagmus usually reflects central lesion; speaker gives example of pure downbeat nystagmus in patient with paraneoplastic cerebellar degeneration; upbeat and torsional nystagmus less well-localizing; upbeat most commonly localized to central medulla, while torsional nystagmus localizes medulla or midbrain

Infantile or congenital nystagmus: conjugate horizontal nystagmus; present from birth or early infancy; often coexisting jerk and pendular waveforms with brief foveation periods; may have normal vision or other afferent visual disorders; often increases significantly with lateral gaze; typically has null zone of minimal symptoms, so patient may adopt head position to compensate

Latent nystagmus: conjugate horizontal jerk nystagmus; absent during binocular vision, apparent only during monocular occlusion; typically seen with congenital strabismus, especially esotropic strabismus; may persist even after strabismus surgery; may have normal vision, amblyopia, or poor binocular vision

Acquired pendular nystagmus: only slow phases; can be horizontal, vertical, torsional or combination; conjugate, sometimes dissociated in its amplitude; commonly associated with multiple sclerosis (MS), in which case usually high frequency, low amplitude; often disabling visually; medication helpful; oculopalatal tremor defined as specific subtype; distinct because of large amplitude, low frequency oscillation combined with synchronous movements of soft palate or other facial or pharyngeal muscles; reflects dysfunction of Mollaret triangle, leading to degeneration of inferior olivary nuclei

Periodic alternating nystagmus: conjugate binocular horizontal jerk nystagmus that spontaneously reverses direction every ≈2 min

See-saw nystagmus: uncommon; eye that goes up intorts, eye that goes down extorts; can occur in jerk or pendular form; lesion usually in midbrain

Pathologic gaze-evoked nystagmus: may be due to leaky neural integrator or first-degree peripheral vestibular nystagmus; other clues (eg, abnormal head impulse test) can help differentiate

Triggered nystagmus: positional, head-shaking induced, smooth-pursuit-induced (sometimes seen with lesions of middle cerebellar peduncle); Tullio phenomenon

Treatment: peripheral vestibular nystagmus — resolves in few days; treat vertigo and nausea as needed; downbeat nystagmus — 4-aminopyridine (4AP) long available in Europe, obtainable in United States through compounding pharmacies; now available as long-acting MS drug dalfampridine (Ampyra; not approved for other indications); acquired pendular nystagmus in MS and oculopalatal tremor — can respond to gabapentin and sometimes memantine; Alzheimer drug; often challenging to obtain insurance coverage for younger patients); periodic alternating nystagmus — effectively treated with baclofen, gamma-aminobutyric acid (GABA) agonist that replaces loss of Purkinje cell inhibitory output; some of these drugs helpful in treating congenital nystagmus but more effective if no additional afferent visual problems present; surgical procedures also used; calcium channelopathies (eg, episodic ataxia type 2) — acetazolamide (Diamox) helpful, as well as 4AP

 

Readings

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