Clinical manifestations

Presentation and course

Nystagmus refers to rhythmic involuntary oscillations of one or both eyes. It can be physiologic or pathologic. There may be associated ophthalmologic or neurologic findings, such as visual loss or ophthalmoparesis. Nystagmus can be described by various qualities, including frequency (number of oscillations per unit of time), amplitude (degree of excursion), and involvement of one or both eyes. Nystagmus may be conjugate (both eyes move together in the same direction) or dysconjugate. Most of the time, nystagmus is present to the same degree in both eyes, but in dissociated nystagmus, there is a difference in the amplitude of the nystagmus between the two eyes. The pattern of nystagmus often varies in different positions of gaze, and in some cases, it is present only in certain positions.

The oscillations in nystagmus can be jerk or pendular in waveform. Jerk nystagmus is much more common and is characterized by a slow phase, during which the eyes move slowly in one direction. Each slow phase is interrupted by a fast phase, during which the eyes move in the opposite direction with a faster velocity. These two phases of different velocity and in opposite directions characterize jerk nystagmus. The direction of the jerk nystagmus is defined by the fast phase (ie, “right-beating nystagmus” refers to fast phase to the right and slow phase to the left). In contrast, in pendular nystagmus, the eyes move back and forth in opposite directions with the same velocity. These “sinusoidal” movements can be in the horizontal, vertical, or torsional planes. A combination of vectors produces circular or elliptical nystagmus.

I. Physiologic nystagmus.

Physiologic gaze-evoked nystagmus. Nystagmus induced by moving the eyes into an eccentric position in the orbit is called gaze-evoked nystagmus. By definition, it is not present when the eyes are in the primary position. In a normal subject, lateral gaze beyond 30 degrees from midline may produce jerk nystagmus that beats in the direction of gaze. This physiologic gaze-evoked nystagmus is also known as end point nystagmus. It is typically nonsustained (few beats only), conjugate, and symmetric on eccentric gaze to the left and right (06; 23). There are a few caveats. With extended maintenance of extreme lateral gaze, nystagmus may be sustained, thought to be due to fatigue from maintaining extreme gaze (29). It should still be symmetric on gaze to the left and right. Additionally, in some cases of physiologic nystagmus, there may be dissociation, with greater amplitude in the abducting eye.

Caloric nystagmus. This form of jerk nystagmus is induced by instillation of cold or warm water into the external auditory canal. Injecting water into an ear creates a current in the endolymph of the horizontal semicircular canal. This causes unequal vestibular activation, simulating head rotation. For example, when warm water is instilled into the left ear, the left vestibular system becomes more active compared to the right. The vestibulo-ocular reflex causes the eyes to drift to the right and, in an awake patient, a corrective left-beating nystagmus attempts to bring the eyes back onto the target of fixation. In the opposite manner, when cold water is instilled into the left ear, there is slow drift of the eyes towards the tested ear, with a corrective fast phase away from the tested ear, resulting in right-beating nystagmus. It must be remembered that the often-used mnemonic “COWS” (referring to “Cold Opposite, Warm Same”) describes the expected direction of fast-phase corrective nystagmus in an awake patient, not the reflexive slow-phase eye movement produced by the vestibular manipulation. Caloric vestibular testing in comatose patients with intact brainstem reflexes produces slow-phase drifting of the eyes, but nystagmus is absent because the corrective fast phase requires cortical function.

Optokinetic nystagmus. The optokinetic reflex allows tracking of a target while it is moving across the visual field (eg, looking outside at passing trees from a moving train). It can be elicited on examination with an optokinetic strip that is made up of stripes. The stripes are moved in a direction (vertical or horizontal), and the patient is asked to silently count the number of stripes. Optokinetic nystagmus is characterized by smooth pursuit in the direction of the movement of the stripes with saccades in the opposite direction to fixate onto the next target that appears within the field of view.

Testing for optokinetic nystagmus can be useful in a variety of ways. Asymmetric loss of optokinetic nystagmus in one direction has localizing value; a deep parietal lobe lesion will often impair smooth pursuit of a stimulus that is moving towards the side of the lesion (41). Another way in which optokinetic nystagmus testing can be helpful is in revealing adduction weakness suggestive of internuclear ophthalmoplegia (29). Vertical optokinetic nystagmus testing can be used to elicit subtle convergence retraction nystagmus, as seen with dorsal midbrain dysfunction. Reverse optokinetic nystagmus (saccades in the same direction of optokinetic nystagmus strip movement and smooth pursuit in the opposite direction) is a finding seen only with congenital nystagmus. Additionally, an intact optokinetic nystagmus response can provide evidence of at least rudimentary visual function in infants or in individuals who are feigning complete visual loss.

II. Pathologic nystagmus.

Congenital nystagmus. Congenital, (now more commonly called “infantile”) nystagmus is typically noted within 6 months of birth. Although the term “congenital” suggests onset at birth, most infantile nystagmus begins at 2 to 3 months of age rather than at birth (31). It usually involves both eyes and is conjugate and horizontal. Its features typically change over the course of development, with decrease in amplitude and increase in frequency. The waveform may be pendular or jerk but is usually a combination of both. It may be found in the presence of ophthalmic disorders that diminish vision (“sensory” form) or may be an isolated manifestation (“motor” form). The principal causes of vision loss in the “sensory” form of congenital nystagmus are corneal and lens opacities, albinism, aniridia, achromatopsia, Leber congenital amaurosis, and optic neuropathy (21).

The distinguishing features of congenital nystagmus can be remembered with the mnemonic CONGENITAL: Convergence and eye closure dampen the nystagmus; Oscillopsia is usually absent; Null zone is present (there is a gaze position at which nystagmus is at its minimum); Gaze position does not change the plane of the nystagmus; Equal amplitude and frequency of nystagmus in each eye; Near acuity is good because convergence dampens the nystagmus; Inversion of optokinetic nystagmus occurs; Turning of head or abnormal head posture to allow eyes to enter a null zone leads to better visual acuity; Absent nystagmus during sleep; Latent nystagmus (see below) occurs (21).

Less than 20% of childhood nystagmus is acquired. Features suggestive of acquired nystagmus include age of onset after 4 months, oscillopsia, dissociated nystagmus, afferent pupillary defect, papilledema, and other associated neurologic signs (11).

• Latent nystagmus. Latent nystagmus (also called “fusion maldevelopment nystagmus”) is a type of congenital jerk nystagmus that is present only when one eye is covered. Therefore, it is usually not recognized until later in life, when one eye is occluded while testing visual acuity during an eye examination. Covering one eye in these patients produces conjugate nystagmus of the eyes away from the covered eye. Some patients may have an associated finding termed dissociated vertical deviation, in which there is upward deviation of the covered eye (08). Latent nystagmus is often associated with infantile esotropia. It does not result from acquired postnatal lesions. Latent nystagmus is usually benign but can be seen in association with periventricular leukomalacia. In “manifest latent nystagmus”, monocular vision loss of any cause results in the nystagmus being present even when both eyes are uncovered (24).

• Periodic alternating nystagmus. See section below on acquired nystagmus.

• Seesaw nystagmus. See section below on acquired nystagmus.

Acquired nystagmus.

• Jerk nystagmus.

- Downbeat nystagmus. Downbeat nystagmus refers to jerk nystagmus with the fast phase beating downward. It is present in primary position of gaze but is often easiest to appreciate when the eyes are in down-and-lateral gaze (39). It is associated with impaired downward smooth pursuit. Downbeat nystagmus is usually caused by impaired function of the cerebellar floccular lobe (15; 38) or a disorder of the cervicomedullary junction (39), such as an Arnold-Chiari malformation (05).

Other etiologies include autoimmune or paraneoplastic spinocerebellar degeneration, celiac disease, hereditary spinocerebellar degeneration, anticonvulsant intoxication (04), magnesium deficiency, brainstem encephalitis (14), lithium use (40), alcoholic cerebellar degeneration (12), and vitamin E deficiency. Patients with downbeat nystagmus should be imaged using an MRI dedicated to the cervicomedullary junction. Paraneoplastic and autoimmune assays as well as magnesium and vitamin E levels can be checked. Of note, the cause of isolated downbeat nystagmus remains idiopathic in up to 40% of cases (12; 38).

- Upbeat nystagmus. This nystagmus is present on primary gaze with the fast phase beating upward. It is virtually always a sign of acquired disease of the brainstem but may localize anywhere from the midbrain to the medulla or to the cerebellum. Upbeat nystagmus with increased amplitude in upgaze is secondary to a cerebellar vermis lesion; upbeat nystagmus that decreases in upgaze suggests a lower brainstem lesion (07). Degenerative conditions, tumors, strokes, intoxications (including nicotine intoxication), and inflammatory processes may be responsible.

- Periodic alternating nystagmus. This form of nystagmus can be acquired or congenital. It is seen on primary gaze and characterized by horizontal jerk nystagmus that periodically changes direction. The usual sequence consists of approximately 90 seconds of nystagmus in 1 direction, followed by 10 to 15 seconds without nystagmus, then nystagmus in the opposite direction. This sequence repeats continuously. This form of nystagmus remains horizontal in vertical gaze. Periodic alternating nystagmus typically localizes to the cervicomedullary junction or flocculonodular lobe of the cerebellum, and possible etiologies include Arnold-Chiari malformation, multiple sclerosis, cerebellar pathology, brainstem infarction, and anticonvulsant toxicity. Brain MRI should be performed (23).

- Nystagmus secondary to internuclear ophthalmoplegia. Nystagmus secondary to internuclear ophthalmoplegia is a manifestation of a lesion within the medial longitudinal fasciculus, most commonly demyelination or ischemia. One component of internuclear ophthalmoplegia is a dissociated nystagmus of the abducting eye on lateral gaze. This form of nystagmus is not usually evident in primary position, becoming evident only when the patient looks in the direction of incomplete adduction (29). The abduction nystagmus is thought to reflect an attempt to overcome adduction weakness in the other eye. Zee and colleagues based this idea on Hering’s law of equal innervation, that an attempt to increase innervation to a weak muscle in one eye must be accompanied by a commensurate increase in innervation to the yoke muscle in the other eye (42).

- Pathologic gaze-evoked nystagmus. In comparison to physiologic gaze-evoked nystagmus (described above), the pathologic form is usually sustained, greater amplitude, present at smaller degrees of eccentric gaze, and asymmetric in different directions of gaze. Pathologic gaze-evoked nystagmus occurs because of difficulty maintaining the eyes in an eccentric position. Due to elastic forces in the orbit, the eyes drift back toward the central position of gaze, whereas corrective fast phase eye movements attempt to return the eyes to the desired eccentric position (23). Pathologic gaze-evoked nystagmus reflects dysfunction of a network of neurons called the neural integrator system that normally allows for eccentric gaze to be sustained. Etiologies include toxic-metabolic processes (eg, sedatives and antiepileptic medications), and lesions in the brainstem or cerebellum causing central vestibular dysfunction.

- Rebound nystagmus. Rebound nystagmus is a phenomenon that occurs when the eyes are held in eccentric gaze and then returned quickly to primary gaze. Transient jerk nystagmus in the opposite direction of the eccentric gaze is seen. Rebound nystagmus is often seen with pathologic gaze-evoked nystagmus and typically signifies a cerebellar lesion. Alcoholic degeneration is a common cause.

- Peripheral vestibular nystagmus. Peripheral vestibular dysfunction can cause various types of nystagmus that depend primarily on whether the process is activating or destructive. Benign peripheral positional vertigo (BPPV) is a common disorder in which there is abnormal activation of a semicircular canal. The type of nystagmus depends on which semicircular canal is involved. In posterior canal BPPV, which is most common, an upbeating torsional nystagmus towards the dependent ear is seen when the Dix-Hallpike maneuver is performed. When the patient is laid down during the maneuver, there is an initial brief latency period without nystagmus that is then followed by the characteristic nystagmus. When the nystagmus begins, it gets progressively faster and then slows down before dissipating. The nystagmus is brief and typically lasts less than 60 seconds. In horizontal canal BPPV, which is less common, horizontal nystagmus is evident during the Supine Roll maneuver. It can either beat towards the ground, referred to as “geotropic,” or away from the ground, referred to as “apogeotropic.” By determining the type of horizontal nystagmus (geotropic or apogeotropic) and whether the nystagmus is more intense with the left or right ear down, one can determine which horizontal canal, left or right, is affected. The rarest type of BPPV involves the anterior canal, and it is sometimes caused iatrogenically after canalith repositioning maneuvers have been performed to treat posterior canal or horizontal canal BPPV. Typically, a downbeating-torsional nystagmus is seen on the Dix-Hallpike maneuver.

Based on the canal that is affected in BPPV, the clinician can perform the appropriate canalith repositioning maneuver. For example, the Epley maneuver is often used to treat posterior canal BPPV and can be initiated directly from a positive Dix-Hallpike maneuver. Once the pathognomonic upbeat-torsional nystagmus elicited on the Dix-Hallpike maneuver subsides, the head is rotated 90 degrees away from the affected ear and held in position for 30 seconds. The head is then rotated another 90 degrees in the same direction and held for 30 seconds before the patient is returned to sitting position. Canalith repositioning maneuvers can be very effective but sometimes need to be repeated (13).

Vestibular neuritis is an inflammatory process affecting the peripheral vestibular system, and often presents with intense vertigo. An imbalance in tonic inputs from the right and left vestibular systems with less input from the affected side results in an involuntary slow phase eye movement towards and a fast phase away from the affected ear. The nystagmus is typically horizontal with a torsional component. Peripheral vestibular nystagmus conforms to Alexander’s law, meaning that the amplitude of the nystagmus is greatest when the eyes are in the direction of the fast phase movement. As an example, a patient with right vestibular neuritis would have left-beating nystagmus that is most apparent in left gaze. If nystagmus is present in right gaze, it would have lower amplitude but would still be left-beating. Unlike central pathologic gaze-evoked nystagmus, peripheral vestibular nystagmus does not change directions in different directions of gaze. Another feature of peripheral vestibular nystagmus is that it is exacerbated when visual fixation is removed. Frenzel goggles or techniques (described in the diagnostic workup section) can be used to remove fixation and see whether the nystagmus becomes more apparent (23).

- Central vestibular nystagmus. In this form of nystagmus, which owes to a lesion in the brainstem vestibular pathway, nystagmus can be spontaneous or triggered by positional change and have horizontal, vertical, and torsional trajectories (30).

Nystagmus trajectories that suggest a central cause include purely torsional, purely vertical, and horizontal direction-changing nystagmus (left-beating in left gaze, right-beating in right gaze). A study found that the presence of a central pattern of nystagmus, a normal head impulse test, or skew deviation was 100% sensitive and 96% specific for stroke in a patient presenting with acute vertigo. This combination of observations has been termed “HINTS” (Head Impulse, Nystagmus, and Test of Skew). The bedside HINTS examination was more sensitive for brainstem stroke than diffusion-weighted brain MRI within the first 48 hours of symptom onset (17). However, the observations were made by a single neuro-ophthalmologist, which may limit their generalizability. In a larger subsequent study that included examiners of different backgrounds, the sensitivity and specificity of the HINTS exam were not as high (18). However, this larger study also included patients without nystagmus in whom the HINTS may not be applicable (27).

- Bruns nystagmus. Bruns nystagmus is characterized by a combination of two different types of nystagmus. Gaze away from the lesion elicits a small-amplitude, high-frequency nystagmus that beats away from the side of the lesion due to ipsilateral vestibular nerve dysfunction. Gaze towards the lesion elicits a coarse, low frequency gaze-evoked nystagmus that beats towards the lesion due to compression of the brainstem. The most likely cause is a large cerebellopontine angle tumor.

- Convergence-retraction “nystagmus.” This eye movement abnormality is seen in dorsal midbrain dysfunction. On attempted upgaze, there is co-contraction of antagonistic extraocular muscles accompanying small upward excursions of the eye, resulting in a nystagmoid appearance. However, this is not a true nystagmus as there is no slow phase. If the convergence retraction nystagmus is subtle, a downgoing optokinetic nystagmus flag can be used to accentuate the finding. Associated findings seen in dorsal midbrain syndrome (Parinaud syndrome) include upgaze palsy, pupillary light-near dissociation, and bilateral lid retraction (Collier sign).

• Pendular nystagmus.

- Spasmus nutans (in children). Spasmus nutans refers to a triad of head tilt, head nodding, and nystagmus. Its onset is usually between 4 and 14 months of age. It typically persists for months to years but usually disappears spontaneously by 5 years of age. The nystagmus often appears to be monocular but is frequently binocular and markedly asymmetric. It is pendular in the horizontal or vertical plane and characterized by high frequency and low amplitude shimmering movements. Head nodding usually appears first and disappears with sleep or changes in head position. Although spasmus nutans is usually benign, similar nystagmus has been reported in optic nerve and chiasmal glioma (32), third ventricular tumor (01), and degenerative disorders. Therefore, the diagnosis of spasmus nutans should be one of exclusion, and children with an acquired monocular or primarily monocular oscillation should be imaged, preferably with an MRI study dedicated to the perichiasmal area.

- Seesaw nystagmus. Seesaw nystagmus is characterized by a binocular pendular nystagmus consisting of alternating elevation and intorsion of one eye and depression and extorsion of the other eye. It may be congenital or acquired. When acquired, this form of nystagmus is usually secondary to large parasellar lesions expanding into the third ventricle. Patients with this form of nystagmus should undergo visual field examination to investigate the possibility of a bitemporal hemianopia (26). An MRI of the brain with attention to the parasellar area should be performed. In the congenital form, there may be no torsional component, or the direction of torsion may be reversed such that the elevating eye extorts and the depressing eye intorts. Hemi-seesaw nystagmus, which can have a jerk waveform, is seen with midbrain lesions.

- Oculopalatal tremor. This term refers to the combination of pendular nystagmus and palatal tremor. There may also be rhythmic movements of other muscles, including the pharynx and the diaphragm. The nystagmus has a frequency of 1 to 3Hz and continues during sleep. Oculopalatal tremor typically appears months after brainstem infarction or hemorrhage. This phenomenon results from disruption of the central tegmental tract of Mollaret’s triangle, which involves the ipsilateral red nucleus, ipsilateral inferior olive, and contralateral dentate nucleus. On MRI, olivary hypertrophy may be seen.

- Oculomasticatory myorhythmia. This rare condition refers to a pendular convergence nystagmus with slow rhythmic movements of the jaw occurring at 1Hz. It is associated with Whipple disease.

- Heimann-Bielscholwsky phenomenon. This phenomenon describes a monocular, coarse, low frequency, pendular vertical nystagmus in an eye with significantly impaired vision. Associated symptoms of diplopia and oscillopsia are rare (09).

Prognosis and complications

Prognosis and complications depend on the form and etiology of the nystagmus.

Clinical vignette

Case 1. A 40-year-old man presented to the office complaining of vertigo. He said that the spinning sensation began suddenly when he turned his head. He also experienced nausea and felt unsteady when he walked. His wife said that he walked as though he were drunk. On examination, the patient’s visual function was normal, including visual acuity, color vision, visual fields, and funduscopic examination. On ocular motility testing, the patient had right-beating nystagmus, which increased in amplitude on looking to the right. There was no nystagmus in left gaze. The nystagmus became more obvious when one eye was shined with light and the other eye was intermittently covered. This is an example of an acute left vestibular neuritis.

Case 2. An 18-year-old man presented with complaints of frequent falls over the past 6 months. His brother reported that “he sounds like he has marbles in his mouth.” When asked, the patient reported that his vision was blurry. He had downbeat nystagmus in primary position that increased in down-and-lateral gaze. An MRI of the brain was performed that revealed an Arnold-Chiari malformation with 16 mm downward herniation of the cerebellar tonsils. He underwent an occipital decompression with improvement in his speech and ataxia. There was slight improvement in the nystagmus.

Case 3. A 25-year-old woman presented with headache, diplopia, and difficulty walking of 4 months duration. On examination, in addition to right fifth, sixth, seventh, and eighth cranial nerve palsies, she had marked gait ataxia. Left plantar was extensor. Examination of eye movements revealed a low frequency, coarse right-beating nystagmus on looking to the right and a high frequency, small amplitude, left-beating nystagmus on looking to the left. MRI of the brain showed a large right cerebello-pontine angle tumor. The combination of these two types of nystagmus is characteristic of Bruns nystagmus.

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Biological basis

Etiology and pathogenesis

Three separate mechanisms are at work to maintain steady gaze: fixation, the vestibulo-ocular reflex, and the neural integrator. Fixation involves the visual system’s ability to detect an eye drift and then program an appropriate corrective movement of the eyes. The vestibulo-ocular reflex produces eye movements to compensate for head movements, thereby providing clear vision when a person is moving. The neural integrator is responsible for sustaining eyes at a desired eccentric position in the orbit against forces of the opposing orbital tissues. Failure of any of these mechanisms may cause the eyes to drift, producing the slow phase of acquired nystagmus (02). Various neurotransmitters are involved in the vestibulo-ocular reflex and other smooth eye movements. Excitatory transmission is probably affected by glutamine and by substance P. Acetylcholine facilitates transmission. Glycine is the inhibitory neurotransmitter for the horizontal vestibulo-ocular reflex. GABA is the inhibitory neurotransmitter for the vertical vestibulo-ocular reflex (33).

Regarding idiopathic infantile nystagmus (infantile nystagmus without associated systemic or ocular abnormalities), the most common form has an X-linked inheritance pattern with mutations in the FRMD7 gene (Xq26.2). Penetrance rates of 100% in males and 53% in females have been reported (31). Forms with an autosomal dominant inheritance pattern have also been reported and mapped to chromosome 6p12 (19), 7p11 (20), and 13q (11). Rare forms with an autosomal recessive inheritance pattern have been described. Clear genotype-phenotype correlations have not been found (11).

Differential diagnosis

The differential diagnosis of the cause of nystagmus depends on the type of waveform and contributory history, and neurologic and systemic abnormalities (see Diagnostic workup, below).

Diagnostic workup

History should elicit whether the patient appreciates oscillopsia (the subjective perception of illusory visual motion), which is not present in congenital nystagmus. Examination includes assessment of visual acuity as well as other tests of optic nerve function, including color vision, visual fields, and pupillary responses.

The eye movements should then be assessed, but the examiner should first note whether the eyes are still as they fixate a target straight ahead (primary gaze position). The patient should then be instructed to follow a moving finger into the extremes of horizontal and vertical gaze. The smoothness and amplitude of tracking should be noted. In some cases, nystagmus may be suppressed by fixation. Therefore, equipment and techniques to remove fixation may be helpful. Frenzel goggles not only magnify the eyes for the examiner but also remove fixation. If these goggles are unavailable, an alternative method is to use an ophthalmoscope. One eye is covered, and the other eye is examined with an ophthalmoscope. The light from the ophthalmoscope removes fixation in the uncovered eye. When using this technique, however, it is important to remember that the direction of optic disc movement seen through the ophthalmoscope is in the opposite direction of the nystagmus (ie, if the optic disc appears to be left-beating through the ophthalmoscope, the nystagmus is actually right-beating). A similar effect of suppressing fixation can also be achieved by shining a bright light on one eye and covering the other eye (28). The amplitude, frequency, and waveform (pendular versus jerk) of nystagmus should be recorded in various fields of gaze.

Finally, a complete neurologic examination should be performed to determine whether any other localizing signs are present. An MRI of the brain should be dedicated to the specific area of possible pathology as determined by the form of nystagmus.

Management

Attempts to reduce nystagmus amplitude, and thereby improve visual acuity or reduce oscillopsia, have been of limited benefit. Current therapies for nystagmus include pharmacologic treatment, optical devices, botulinum toxin injections, and eye muscle surgery.

Various pharmacologic agents are available for different types of nystagmus (37). For downbeat nystagmus, potassium channel blockers 4-aminopyridine and 3,4-diaminopyridine effectively suppress downbeat nystagmus. Main side effects include insomnia, dizziness, headache, and paresthesias. Notably, these medications are contraindicated in patients with a history of seizures as they can increase seizure risk. Clonazepam is also commonly used for downbeat nystagmus. For upbeat nystagmus, first-line drugs include memantine, 4-aminopyridine, and baclofen (37). Baclofen has been found to reduce the slow phase of the nystagmus and the distressing oscillopsia in some patients with downbeat and upbeat nystagmus (10). Periodic alternating nystagmus is most effectively treated with baclofen and memantine (16).

Most nystagmus from acute peripheral vestibular dysfunction, such as vestibular neuritis, resolves spontaneously. Treatment is aimed at reducing vertiginous symptoms, and commonly used medications include benzodiazepines and antihistamines, such as meclizine and diphenhydramine. Using these medications for longer than 3 days is not advised because it may interfere with central nervous system compensation. When performed correctly, canalith repositioning maneuvers are highly effective for the treatment of BPPV (13).

For pendular nystagmus seen in multiple sclerosis and oculopalatal tremor, gabapentin and memantine can be used. A multicenter double-blind crossover trial found that gabapentin 900 mg/day was more effective than standard doses of baclofen in the treatment of acquired pendular nystagmus and resulted in improved visual acuity (03). Gabapentin significantly reduced the movements in all planes whereas baclofen reduced movement only in the vertical plane. In an unmasked study involving 11 patients with pendular nystagmus from multiple sclerosis, those who were given memantine had complete cessation of nystagmus (36). For seesaw nystagmus, drugs that have been used include clonazepam, memantine, baclofen, and gabapentin (24; 37; 25).

Patients with congenital nystagmus whose nystagmus amplitude is reduced by convergence may gain slight improvement in visual acuity from spectacle prisms that elicit convergence as the patient fixates distant targets.

An optical device that stabilizes images on the retina has also been somewhat beneficial in improving oscillopsia and visual acuity in patients with acquired periodic alternating nystagmus (35).

Injection of botulinum toxin into the extraocular muscles or retrobulbar space has been used to temporarily reduce or abolish acquired nystagmus (22). However, its usefulness has been limited by need for repeated injections and complications, including diplopia and ptosis.

Surgical weakening of the extraocular muscles has also been used in treatment of acquired pendular nystagmus with limited success. Surgical procedures designed to improve visual acuity in patients with congenital nystagmus have been somewhat more successful. The Kestenbaum operation for congenital nystagmus moves the attachment of the extraocular muscles so that the null or quiet zone of nystagmus corresponds to the primary position of gaze (33). It is performed after measuring the nystagmus intensity in various positions of gaze and determining the null point. The Kestenbaum procedure shifts and broadens the null point and dampens the nystagmus in other positions of gaze. It is generally not indicated unless the patient has a large face turn, and visual acuity is much better when the eyes are positioned in the null zone than outside the null zone. A second surgical procedure is the artificial divergence procedure of Cuppers. It is helpful only in patients with congenital nystagmus whose nystagmus markedly dampens and visual acuity improves at reading distance. Neurosurgical decompression of Arnold-Chiari malformation may reduce the amplitude of downbeat nystagmus, but patients should be advised that substantial lessening of oscillopsia after surgery is not likely (23).