A condition in which there is involuntary movement of the eyes.
In the most common type, jerky nystagmus, the eyes repeatedly move slowly in one direction and then rapidly in the other. Less commonly, nystagmus is “pendular”, with the eyes moving evenly from side to side.
Nystagmus may be congenital, in which case the cause is unknown. It also occurs in albinism and as a result of any very severe defect of vision present at birth, such as congenital cataract.
Persistent nystagmus appearing later in life usually indicates a nervous system disorder (such as multiple sclerosis, a brain tumour, or an alcohol-related disorder), or a disorder of the balancing mechanism in the inner ear. Adultonset nystagmus is occasionally seen as an occupational disorder in people who work in poor light.
Electronystagmography, a method of recording eye movements, may be used to identify the type of nystagmus.
See under EYE, DISORDERS OF.
n. rapid involuntary movements of the eyes, which may be from side to side, up and down, rotatory, or a mixture. Nystagmus may be congenital and associated with poor sight; it also occurs in disorders of the part of the brain responsible for eye movements and their coordination (e.g. multiple sclerosis) and in disorders of the organ of balance in the ear or the associated parts of the brain. Certain drugs, especially in excessive doses (e.g. phenytoin), also cause nystagmus. Optokinetic nystagmus occurs in normal people when they try to look at a succession of objects moving quickly across their line of sight. Jerking eye movements sometimes occur in normal people when tired, on concentrating their gaze in any direction. These are called nystagmoid jerks and they do not imply disease.
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