Acquired nystamusHistoryImportant aspects of the history include the following: Age of onset of the nystagmus, whether it is constant or intermittent, the presence of any aggravating or alleviating factors (eg, head position) Presence or absence of vertigo, oscillopsia (an illusory motion of the seen world),[10]and sensation of disequilibration suggest a lesion of the vestibular system. Deafness or tinnitus is present with peripheral lesions of the vestibular system. Presence of diplopia, particularly in certain positions of gaze: Patients with INO may report diplopia only on lateral gaze or intermittent blurring of vision. Ask questions regarding the presence of any associated symptoms, such as symptoms related to demyelinating disease (eg, a history of loss of vision, eye pain, or numbness or weakness of the extremities), symptoms related to cerebrovascular accident (eg, hemiplegia).PhysicalA complete neuro-ophthalmic examination is imperative in patients with nystagmus. Aside from a complete ophthalmic examination, including visual acuity, measurement and reactivity of the pupils to light and accommodation, measurement of intraocular pressure, testing the function of extraocular muscles, and anterior and dilated posterior segment examination, other important aspects of the examination include the following: Observing the nystagmus with regard to type (eg, horizontal, vertical), frequency, amplitude, direction, and conjugate/disconjugate is important. Pure vertical, pure horizontal, or pure rotary nystagmus almost always represents central vestibular dysfunction. Note whether the character of the nystagmus changes in certain directions of gaze. Nystagmus due to vestibular disease increases in intensity when the eyes are turned in the direction of the saccade (fast phase), ie, Alexander law. A horizontal nystagmus due to peripheral vestibular imbalance remains horizontal on upward and downward gaze. Note the presence or absence of head nodding or torticollis (spasmus nutans). Note whether the nystagmus dampens with fixation. Fixation inhibits nystagmus and vertigo due to peripheral lesions of the vestibular system. Optokinetic nystagmus (OKN) drum: The optokinetic reflex allows us to follow objects in motion when the head remains stationary (eg, observing individual telephone poles on the side of the road as one travels by them in a car). The reflex develops at about age 6 months. The normal eye movements that one observes depend upon the orientation of the drum in front of the patient. If the drum is held in front of the patient with the bars directed vertically and is spun to the left (the patient's right), one would observe a slow pursuit movement of the eyes to the patient's right as a moving bar is followed, then a quick saccade to the patient's left as the patient searches for the next moving bar to fixate on and again follows that bar with a slow pursuit movement to the patient's right. This reflex is abnormal in patients with congenital nystagmus. One may observe a paradoxical reversal of the optokinetic nystagmus response. Patients with horizontal nystagmus with unilateral hemispheric lesions, especially parietal or parietal-occipital lesions, show impaired optokinetic nystagmus when the drum is rotated toward the side of the lesion. The OKN drum may be used as an estimate of visual acuity. The striped drum is equivalent to a vision of counting fingers when held at a distance of 3-5 feet from the patient. The further the drum is from the patient, the better the visual acuity must be to respond normally to the moving drum. Confrontational visual field testing may reveal gross field defects that may help determine the presence and/or location of an intracranial lesion. For Romberg testing have the patient stand with eyes closed and feet together. If a defect in the vestibular system is present, the patient tends to fall toward the side of the lesion. Oculocephalic reflex (doll's head phenomenon) The oculocephalic reflex develops within the first week of life and essentially represents a vestibulo-ocular reflex normally suppressed in a conscious individual that attempts to turn the head to fixate on an object. This test consists of the rapid rotation of the patient's head in a horizontal or vertical direction. With intact vestibular nuclei and medial longitudinal fasciculi, the eyes move conjugately in the opposite direction of the head turn. Alternatively, the test may be performed by having the patient extend the arm out in front of the body and fixate on the outstretched thumb. Patients should be instructed to rotate their torso back and forth about their longitudinal axis such that the thumb remains in front of the body at all times. Patients with the ability to suppress the oculocephalic reflex should be able to maintain fixation on their thumb while rotating. An abnormal test result would show the patient continuously losing fixation of the thumb. Inability to suppress the oculocephalic reflex is common in patients with vestibular imbalance. Caloric testing Instilling cold or warm water into the external auditory canal can reproduce the same movement of endolymph in the semicircular canals produced by rotations of the head. Instillation of water into the external auditory canal causes endolymph convection currents that in turn induce nystagmus. While sitting erect, the patient tilts the head back 60. While in supine, the patient elevates the head 30; this brings the horizontal semicircular canals into the vertical plane. The external auditory canal is irrigated with cold or hot water. Cold water instilled into the right ear causes the endolymph in the right semicircular canal to cool and sink. This movement of endolymph is the same movement induced by a rotation of the head to the left, inducing a horizontal nystagmus directed to the left (ie, to the opposite side the water was placed). Warm water in the same ear produces the opposite effect (ie, a horizontal nystagmus directed to the right or toward the same side the water was placed); ie, cold-opposite, warm-same (COWS). Note whether the character of the nystagmus changes with otolithic stimulation. Failure to respond to otolithic stimuli implies peripheral vestibular disease.Causes Seesaw nystagmus Rostral midbrain lesions Parasellar lesions (eg, pituitary tumors) Visual loss secondary to retinitis pigmentosa Downbeat nystagmus Lesions of the vestibulocerebellum and underlying medulla, including the following: Arnold-Chiari malformation Demyelination (eg, multiple sclerosis)[14] Microvascular disease with vertebrobasilar insufficiency Brain stem encephalitis Tumors at the foramen magnum (eg, meningioma, cerebellar hemangioma) Trauma Drugs (eg, alcohol, lithium, antiseizure medications) Nutritional (eg, Wernicke encephalopathy, parenteral feeding, magnesium deficiency) Heat stroke Approximately 50% have no identifiable cause. Upbeat nystagmus Medullary lesions, including perihypoglossal nuclei, the adjacent medial vestibular nucleus, and the nucleus intercalatus (structures important in gaze holding) Lesions of the anterior vermis of the cerebellum Benign paroxysmal positional vertigo Periodic alternating nystagmus Arnold-Chiari malformation Demyelinating disease Spinocerebellar degeneration Lesions of the vestibular nuclei Head trauma Encephalitis Syphilis Posterior fossa tumors Binocular visual deprivation (eg, ocular media opacities) Pendular nystagmus Demyelinating disease Monocular or binocular visual deprivation Oculopalatal myoclonus Internuclear ophthalmoplegia Brain stem or cerebellar dysfunction Spasmus nutans Usually occurs in otherwise healthy children Chiasmal, suprachiasmal, or third ventricle gliomas may cause a condition that mimics spasmus nutans. Torsional - Lateral medullary syndrome (Wallenberg syndrome) Abducting nystagmus of internuclear ophthalmoplegia Demyelinating disease Brain stem stroke Gaze evoked Drugs - Anticonvulsants (eg, phenobarbital, phenytoin, carbamazepine) at therapeutic dosages AlcoholCongenital nystagmus HistoryThere is often a known family history of this disorder. The pattern of heredity is usually sex-linked, with dominant being more common.Establishing the precise age of onset is helpful in differentiating between sensory deficit and idiopathic infantile forms. Spasmus nutans rarely is seen prior to age 4 months. Onset prior to age 2 months, particularly in the setting of gaze-associated variable intensity and torticollis, strongly suggests idiopathic infantile nystagmus.Patients with infantile nystagmus due to albinism may have a positive family history and often appear photosensitive. A history of infantile strabismus increases the likelihood of latent or manifest latent nystagmus.A history of abnormal head movements (bobbing or nodding) or torticollis raises the possibility of spasmus nutans.CNS disease can produce many other forms of nystagmus and always must be considered. A history of failure to thrive or other evidence of neurologic dysfunction should prompt immediate investigation.Older children and adults with a history of infantile nystagmus typically deny oscillopsia but frequently may have signs and symptoms of accommodative dysfunction. These signs and symptoms include asthenopia, headaches, avoidance of near tasks, tearing, and blurry vision.Both idiopathic infantile nystagmus and many forms of sensory deficit nystagmus have a familial pattern. X-linked, autosomal dominant, and autosomal recessive modes of inheritance have been reported.PhysicalBoth sensory deficit nystagmus and idiopathic infantile nystagmus are almost always bilateral, symmetric, and conjugate.[2]Eye movements usually are horizontal and remain so during vertical gaze (uniplanar) rather than changing to a gaze-evoked vertical nystagmus. The nystagmus disappears during sleep.The nystagmus movements may be pendular or jerk in nature. The nystagmus may be intermittent or continuous. The congenital nystagmus patient may have good vision or poor vision. There is no oscillopsia. There may be an inversion of the optokinetic reflex.Nystagmus intensity (a product of the frequency and amplitude) often increases with fixation effort, attention, or anxiety, and diminishes with convergence.Various waveforms have been described. Both pendular and jerk types have been documented to occur in idiopathic infantile and sensory deficit nystagmus. Nystagmus associated with albinism has characteristics similar to idiopathic infantile nystagmus. Latent and manifest latent nystagmus always are jerk-type with the fast phase in the direction of the fixing eye and decreasing velocity of the slow phase; the nystagmus is larger in the amblyopic or nonfixing eye, and amplitude decreases in adduction. Spasmus nutans classically is a triad of nystagmus, head nodding, and torticollis. The nystagmus is disconjugate, high frequency, small amplitude, pendular, and intermittent. It is suppressed with head nodding. A head tilt often is present. Spasmus nutans often disappears after a few years.The hallmark of idiopathic infantile nystagmus is a gaze-dependent, variable intensity resulting in a "null zone" where nystagmus is least marked and visual acuity is maximized. This often corresponds to adoption of an anomalous head posture and is frequently the stated reason for referral.CausesIdiopathic infantile nystagmus is believed to be due to a primary abnormality in oculomotor control. Increasing evidence suggests a genetic mechanism with one gene mapped to the X chromosome and another gene mapped to band 6p12. Hackett et al have found evidence that mutations in the calcium/calmodulin-dependent serine protein kinase (CASK) gene are frequently associated with congenital nystagmus and X-linked mental retardation.[3]Many ocular disorders have been associated with sensory deficit nystagmus. This is not meant to be an exhaustive listing. The variety of sensory causes suggests that the underlying cause is a failure of sensorimotor integration due to reduced vision and/or contrast sensitivity. See the following: Early (usually bilateral) visual deprivation (eg), congenital cataracts, severe glaucoma, Peters anomaly[4] Foveal hypoplasia (eg, aniridia, albinism [nystagmus associated with albinism has characteristics similar to idiopathic infantile nystagmus]) Retinal disease (eg, Leber congenital amaurosis, achromatopsia, macular toxoplasmosis [especially if bilateral]) Retinal detachment (eg, severe retinopathy of prematurity, posterior persistent hyperplastic primary vitreous, familial exudative vitreoretinopathy) Optic nerve abnormalities (eg, hypoplasia, coloboma, atrophy) Cortical visual impairment from perinatal insult or structural CNS abnormalityNystagmus associated with albinism is the result of multifactorial visual impairment. Anatomical findings include abnormal ocular pigmentation, foveal hypoplasia, abnormally increased chiasmal decussation, and high cylindrical refractive errors. Several subtypes have been described. Most are autosomal recessive, but all modes of inheritance have been described.Latent nystagmus is a conjugate, jerk nystagmus with the fast phase toward the side of the fixing eye. It is often seen in patients with congenital esotropia and following surgery for infantile esotropia, probably resulting from subnormal binocular interaction. Latent nystagmus can coexist with manifest nystagmus (in which case the nystagmus amplitude increases with occlusion). Latent nystagmus is a jerk nystagmus with the fast phase toward the side of the fixing eye. It often is seen following surgery for infantile esotropia and probably results from subnormal binocular interaction. Visual acuity measurement should be performed using the polarized vectograph or blurring one eye with a high plus lens to avoid iatrogenic reduction of acuity with occlusion. So-called manifest latent nystagmus can occur if monocular visual loss occurs in this setting.The cause of spasmus nutans is unknown. Some studies have found an association with children from lower socioeconomic status, as well as coexisting strabismus and refractive error. Chiasmal glioma can present with an identical appearing nystagmus prior to affecting the anterior visual pathway. It may be more common in African Americans and in LatinosTREATMENTS- hertleThere are a number of signs and symptoms due to nystagmus that are amenable to treatment. The rst and most obvious is decreased vision (central visual acuity, gaze- angle acuity, near acuity). Correction of signi cant refractive errors in children with nystagmus is the single most powerful therapeutic intervention for improving vision and visual function in these patients. Refractive etiologies of decreased vision include either one or a combination of conditionse.g., myopia, hyperopia, astigmatism, and anisometropia. These refractive conditions can contribute signi cantly to already impaired vision in patients with other organic etiologies of decreased visione.g., amblyopia, optic nerve and / or retinal disease, oscillopsia, and the oscillation itself. The second

Optical Treatments13Convergence prisms provide one optical approach for patients with congenital or acquired nystagmus whose nystagmus dampens when they view a near target (242,523); a useful starting point is 7.00-diopter base-out prisms combined with -1.00-diopter spheres to compensate for accommodation (although the spherical correction may not be needed in presbyopic individuals). In some patients with congenital nystagmus, the resultant improvement of vision is sufficient for them to qualify for a driver's license. Patients whose nystagmus is worse during near viewing may benefit from wearing base-in (divergence) prisms (64).Theoretically, it should be possible to use prisms to help patients whose nystagmus is reduced or absent when the eyes are moved into a particular position in the orbit: the null region. For patients with congenital nystagmus, there is usually some horizontal eye position in which the nystagmus is minimized, whereas downbeat nystagmus may decrease or disappear in upgaze. In practice, patients use head turns to bring their eyes to the optimum position, and only rarely are prisms that produce a conjugate shift helpful.A different approach to the treatment of nystagmus has been the use of an optical system that stabilizes images on the retina (524). This system consists of a high-plus spectacle lens worn in combination with a high-minus contact lens. The system is designed on the principle that stabilization of images on the retina could be achieved if the power of the spectacle lens focused the primary image close to the center of rotation of the eye. However, such images are then defocused, and a contact lens is required to extend the clear image back onto the retina. Since the contact lens moves with the eye, it does not negate the effect of retinal image stabilization produced by the spectacle lens. With such a system, it is possible to achieve up to about 90% stabilization of images upon the retina. There are several limitations to the system, however. One is that it disables all eye movements (including the vestibulo-ocular reflex and vergence) and thus is useful only when the patient is stationary and is viewing monocularly. Another limitation is that with the highest-power components (contact lens of -58.00 diopters and spectacle lens of +32diopters), the field of view is limited. Some patients with ataxia or tremor (such as those with MS) have difficulty inserting the contact lens. However, initial problems posed by rigid polymethyl methacrylate contact lenses can be overcome by using gas-permeable, or even soft contact lenses (525). Most patients do not need the highest power components for oscillopsia to be abolished, and vision to be improved. We have found that in selected patients the device may prove useful for limited periods of time, for example, if the patient wishes to watch a television program (526).Contact lenses alone sometimes suppress congenital nystagmus (527). This effect is not from the mass of the lenses but is probably mediated via trigeminal afferents (528); this issue is discussed further below.A more recent innovation has been to use an electronic circuit to distinguish between the nystagmus oscillations and normal eye movements (529). This approach is most applicable in patients with pendular nystagmus. Eye movements are measured using an infrared sensor and, after filtering, fed to a phase-locked loop that generates a signal similar to the nystagmus but is insensitive to other eye movements, such as saccades. This electronic signal is then used to rotate Risley prisms, through which the patient views the environment. When the Risley prisms rotate in synchrony with the patients nystagmus, they negate the visual effects of the ocular oscillations. Improvement and miniaturization of a prototype device may eventually lead to a spectacle-mounted device that selectively cancels out the visual effects of pathological nystagmus (529,530).The main therapy for latent nystagmus consists of measures to improve vision, particularly patching for amblyopia in children (531).

Surgical Procedures for NystagmusTwo surgical procedures may be effective for certain patients with congenital nystagmus. One is the Anderson-Kestenbaum operation (538,539,540). This procedure is designed to move the attachments of the extraocular muscles so that the new central position of the eyes is at the null position. It is performed after first making careful eye movement measurements of nystagmus intensity with the eyes in various positions of gaze and determining the approximate null position. The appropriate extraocular muscles are then weakened or strengthened as necessary to achieve the required shift in the position of the null (541,542,543). The Anderson-Kestenbaum procedure not only shifts and broadens the null region, but also results in decreased nystagmus outside the region. It is of uncertain value in the treatment of acquired forms of nystagmus.The second procedure is an artificial divergence operation (544,545). It may be helpful in patients with congenital nystagmus that dampens or is suppressed during near viewing and who have stereopsis. Studies comparing these two methods indicate that the artificial divergence operation generally P.1165

results in a better visual outcome than the Anderson-Kestenbaum procedure alone (543,545,546,547).Several authors have recommended performing large recessions of all of the horizontal rectus muscles for treatment of patients with congenital nystagmus (548,549). Based on a long experience, Dell'Osso noted that any surgical procedure that detached and reattached the extraocular muscles tended to suppress congenital nystagmus. This led him to suggest that simply dissecting the perimuscular fascia and then reattaching the muscles at the same site on the globe might prove effective, especially in cases when convergence does not dampen the nystagmus. Results of this procedure on a canine model for congenital nystagmus supported this hypothesis (550). Reported lack of effect in monkeys concerns latent nystagmus, not typical congenital nystagmus (551,552). Preliminary results of a large, controlled clinical trial suggest that the operation is effective in some patients (242,553).How could such a procedure damp congenital nystagmus? Recent studies by Bttner-Ennever and colleagues have indicated that the terminal portion of the extraocular muscles, near their site of their attachment, contains multiply-innervated muscle fibers (554). Using rabies toxin as an anatomic tracer, it has been possible to show that a separate group of ocular motor neurons (distinct from the classic oculomotor, trochlear, and abducens nuclei, and surrounding each of them) innervates these multiply-innervated fibers.Finally, it is known that ocular proprioceptors (the pallisade organs) lie at the insertion site of the extraocular muscles (554). Thus, procedures similar to those proposed by Dell'Osso may work by disrupting a proprioceptive feedback pathway that normally sets the tone of the extraocular muscles.There is also some evidence that the tendino-scleral junction may contain neurovascular abnormalities in the eyes of patients with congenital nystagmus (555). This suggestion, and the orbital revolution set in motion by the discovery of pulleys for the extraocular muscles by Miller and Demer, promise the development of new therapies for congenital nystagmus (556).The role of surgery in the treatment of acquired nystagmus is not well established, although individual patients may benefit from recession operations (506,557). However, it is clear that suboccipital decompression improves downbeat nystagmus in Chiari syndromes and also prevents progression of other neurologic deficits (558,559,560).As noted above, SOM that does not respond to treatment with medication may respond to extraocular muscle surgery. The procedure used by most surgeons is a superior oblique tenectomy combined with myectomy of the ipsilateral inferior oblique muscle (414,415,417,422,561). However, Kosmorsky and colleagues reported successful treatment of a patient with SOM by performing a nasal transposition of the anterior portion of the affected superior oblique tendon, thereby weakening cyclorotation (562).Other Forms of TreatmentA variety of methods other than those described above have been used to treat nystagmus, principally the congenital variety. Electrical stimulation or vibration over the forehead may suppress congenital nystagmus (264). The mechanism of vibration on eye movements is uncertain, since vibration over the mastoid in patients who have lost vestibular function induces ocular torsion (563). However, it is postulated that the suppressive effect on congenital nystagmus, as well as suppression induced by wearing contact lenses (528), may be exerted via the trigeminal system, which receives extraocular proprioception (264,554).Acupuncture administered to the neck muscles may suppress congenital nystagmus in some patients via a similar mechanism (564,565). Biofeedback has also been reported to help some patients with congenital nystagmus (566,567). The role of any of these treatments in clinical practice has yet to be demonstrated.

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