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CONGENITAL NYSTAGMUS (CN)

Timothy C. Hain, MD Page last modified: December 30, 2007

Congenital nystagmus (CN) is a term which is applied a diverse group of abnormal eye movements which are noted at birth or shortly thereafter. Congenital nystagmus is included under the category of disorders of fixation because it can frequently present as a severe gaze-evoked nystagmus, and because it is often increased by attempts at fixation. Congenital nystagmus is universal in albinism and also occurs in achromatopsia. Such patients usually show rounding of slow-phases, with convexity in the direction of gaze. Such "increasing exponential velocity profiles" are typical of congenital nystagmus.

CN is often (although not always - -see torsional movie above) a dramatic nystagmus, difficult to miss if one looks at the eyes at all. No special procedure is required to elicit congenital nystagmus, other than that described for registration of gaze-evoked nystagmus, saccades or spontaneous nystagmus. The saccade protocol is most suitable because CN often varies with orbital position and is strongest in the light.

Once again, congenital nystagmus, contrary to vestibular nystagmus, is generally increased by fixation and reduced in the dark. This is an important distinguishing feature.

In this movie of jerk type Congenital nystagmus in dark (3 megabytes), the same patient as above is being recorded with a video system in complete darkness. Note that the nystagmus has nearly abated.

Another typical feature of congenital nystagmus is that there is often a "null". This is a position of the eyes in the orbit where the eyes are nearly still. Often people with CN adopt a head posture which allows them to put their eyes into this "null", to improve their visual acuity.

Persons with CN generally do as well in life as persons without CN. Ordinary testing for dizziness (such as an ENG or rotatory chair testing) is difficult to interpret in persons with CN, and generally we tend to avoid doing it, except in difficult cases.

Differential diagnosis of CN

Generally diagnosis of CN is easily made by observing a typical nystagmus as described above, obtaining a history of nystagmus since an early age, and noticing that the nystagmus is decreased in the dark.

Nevertheless, there are several types of acquired nystagmus that appear similar to congenital nystagmus.

Nystagmus of the blind is a constantly present nystagmus which may undergo periodic changes in direction. It may be jerk or pendular.

Periodic alternating nystagmus (PAN) may also resemble jerk type CN. The congenital form usually has a short cycle as shown in this movie. This individual's cycle is about 2 seconds, while the usual type of aquired PAN has a cycle of about 200 seconds.

Spasmus Nutans. Notice the pendular nystagmus, about 1 cycle/second. Recording method: ENG. (c) Timothy C. Hain, M.D.

Spasmus nutans (see figure above) consists of a pendular, dysconjugate nystagmus accompanied by head-nodding, which occurs in children. Ocular recordings in patients with spasmus nutans may show a phase difference between oscillations in each eye, or in other words, may dissociated. Spasmus nutans usually remits within 1-2 years of onset although it may persist for eight years or more.

Similar acquired pendular nystagmus in adults can be caused by multiple sclerosis, and follow brainstem infarcts. An example is oculopalatal myoclonus syndrome.

Acquired pendular nystagmus may have components about any axis - -horizontal, vertical or torsional. Sometimes it is present in both horizontal and vertical planes, creating a diagonal or elliptical pattern. Ellipses are due to two sine-waves that have different phases. While there probably is a combination of torsional with horizontal/vertical plane, the resulting "elliptical" nystagmus has never been reported.

Differences in phase or amplitude between eyes is often seen in acquired pendular nystagmus. Acquired pendular nystagmus may be temporarily suppressed by saccades.

Occasional central nystagmus patterns, such as those related to Wernicke's encephalopathy, may have increasing-exponential velocity profiles similar to those seen in some forms of congenital nystagmus.

Occasional central nystagmus patterns may also present simply with a primary position nystagmus (such as this torsional nystagmus due to a midbrain lesion).

An autosomal dominant pedigree linked to chromosome 6p12 was recently described (Kerrison JB et al, 1998).

One must be cautious when using infrared oculography for registration of congenital nystagmus and gaze-evoked nystagmus because artifact due to transducer nonlinearity can cause an ordinary gaze-evoked nystagmus to resemble the increasing exponential pattern described above. Care must be also taken that an unusually intense gaze-evoked nystagmus (usually due to a cerebellar problem) is not mistaken for congenital nystagmus. A distinguishing factor here is that CN generally is present in central gaze, while gaze-evoked nystagmus is generally not. However, even this rule can be broken in persons with a combined vestibular nystagmus and gaze-evoked (i.e. Alexander's law).

Latent Nystagmus

Supplemental material on the site DVD: Video of latent nystagmus

Latent nystagmus is a variant of congenital nystagmus although some authors prefer to reserve the term congenital nystagmus for other variants. It is mainly encountered in persons with strabismus and amblyopia. In the most common form, the nystagmus appears only when one eye is covered. When both eyes are viewing, no nystagmus is seen. This is the reason why it is called "latent" nystagmus. It can be recognized because the eyes always move with their slow-phase towards the nose for the viewing eye. In other words, the direction of the nystagmus in both eyes changes with the viewing eye. The figure below shows a right beating nystagmus, associated with left eye viewing. Recording method is infrared.

 

Latent nystagmus can be very confusing to people attempting to do an ENG. The eyes may jump left or right seemingly at random, and even worse, the unfavored eye commonly deviates to one side depending on which eye is viewing. In a person with a strong latent nystagmus, it can be difficult to make much of anything out of the ENG. The author has encountered patients who were misdiagnosed by ENT doctors as having more serious conditions (such as a perilymph fistula), because the otherwise quite expert examiner simply did not recognize a strong latent nystagmus.

There are a few variants of latent nystagmus.

The most common variant of latent nystagmus is difficult to see with both eyes viewing, and becomes apparent only when one or the other eye is blocked. This is just called "latent nystagmus".

Manifest latent nystagmus is latent nystagmus that can be seen even with both eyes viewing. MLN can be acquired, presumably due to a change in the eye that one habitually views.

In voluntary latent nystagmus, people purposefully view out of either eye, and thus make their eyes jump in either direction at will.

Dissociated vertical deviation or DVD is a vertical strabismus characterized by a slow upward rotation of one eye without movement of the other.

Often persons with latent nystagmus develop a torsional deviation to their eye when they look away from center, which has to be corrected when they return fixation to center. This can be a way of spotting latent nystagmus using video frenzel goggles, during the saccade test.

Treatment of congenital nystagmus

Gabapentin is often useful in reducing the speed of congenital nystagmus. Gabapentin increases an inhitory neurotransmitter used in oculomotor function. We nearly always offer the option of taking gabapentin to patients with CN in our clinic setting in Chicago.

Recently, it has also been reported that Memantine (an agent which acts on asparate, glutamate and dopamine) is also helpful (Mclean et al, 2007). Glutamate is a major excitatory neurotransmitter. Memantine was used in doses of 40 mg -- greater than is commonly prescribed for other uses.

Surgical treatment is also sometimes offered -- mainly involving moving the eye so that the "null" is located more centrally. We have not found this to be very helpful.

References:

Congenital Nystagmus
Copyright August 3, 2016 , Timothy C. Hain, M.D. All rights reserved. Last saved on August 3, 2016