Timothy C. Hain, MD Page last modified: December 28, 2014
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 often show unusual slow-phases, with convexity in the direction of gaze. Such "increasing exponential velocity profiles" are typical of congenital nystagmus.
In albinism anomalous connections through the optic chiasm may result in reversed circuitry for feedback of eye velocity. This positive feedback loop may result in pendular nystagmus or increasing exponential nystagmus as shown above. Most white cats and all Siamese cats are at least partly albinos and all have nystagmus.
Common features of CN:
CN is often (although not always - -see torsional movie above) a dramatic nystagmus, difficult to miss if one looks at the eyes carefully. No special procedure is required to elicit congenital nystagmus, other than that described for registration of gaze-evoked nystagmus, saccades or spontaneous nystagmus. The spontaneous nystagmus shows the characteristic worsening in the light. 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. This page shows a series of images from an rotatory chair from a patient with CN. It can easily be appreciated that there is little vestibular diagnostic information, although it is very clear that the patient has CN.
The following three traces (case1) are from a patient with CN due to an early life visual disorder.
|CN: Much stronger nystagmus is typical in the light (fixation) than in the dark. This is the easiest way to tell CN from nearly any other type of nystagmus.|
|CN: horizontal pursuit is interrupted by strong nystagmus||Tracking is reversed -- slow phases go in opposite direction as pursuit stimulus.|
|CN: OKN may be absent (as here) or inverted. In case2, OKN is overwhelmed by 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:
This is a constant 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. Some persons with CN alternate -- in central gaze, their eyes first jerk to the left and to the right, often at very short intervals. This is not a true PAN, but rather an adaption to CN.
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.
These 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 (see also this page)
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.
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. It seems likely that pregabalin would work too, but we have not tried it as yet. Pregabilin costs more than gabapentin, but is easier to dose.
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. We have never found a patient who responded to memantine, but we have not tried it often.
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, and think in general that it is a bad idea.
|© Copyright December 28, 2014 , Timothy C. Hain, M.D. All rights reserved. Last saved on December 28, 2014|