Nystagmus is an involuntary, repetitive eye movement which usually results in some degree of visual loss, and may be associated with other, more serious conditions that limit vision. The degree and direction of eye movement, amount of visual loss and resulting impairment varies greatly from person to person. Nystagmus may be one of several infantile types or may be acquired later in life.
Nystagmus which occurs in infancy has many names including Congenital Nystagmus(CN), Infantile Nystagmus(IN) and early onset Nystagmus. Many people with these disorders lead normal, active lives. Those with very poor vision usually have associated sensory deficits responsible for the greater part of their vision loss.
Each year thousands of adults develop(acquire) nystagmus,due to other medical conditions such as strokes and Multiple Sclerosis(MS). These are often associated with oscillopsia (the experience of the world ‘wiggling’), poor vision, and loss of balance. Often acquired nystagmus is a result of neurological problems and may respond to certain drugs, depending on the cause of the nystagmus.
DEPTH OF FIELD VISION is not reduced by nystagmus; it results from strabismus (misalignment of the eyes). Strabismus may sometimes accompany CN. Sufferers of strabismus do not develop strong stereoscopic (3-dimensional) vision and may be prone to tripping or clumsiness. Coordination is usually adequate for most tasks, but strabismus sufferers are unlikely to excel at sports needing good hand to eye coordination.
INCIDENCE. Experts agree that congenital nystagmus affects about one in several thousand people. One survey in Oxfordshire, England identified one in every 670 children by the age of two.
CAUSES. Nystagmus may be inherited, be idiopathic (no known cause), or be associated with a sensory problem; its direct cause is an instability in the motor system controlling the eyes. Rarely, CN can develop in later life; acquired nystagmus may be a result of an accident or a range of illnesses, especially those affecting the motor system. You should always consult a doctor if you or a member of your family has nystagmus.
EFFECTS. Nystagmus affects different people in different ways. While there are general patterns, good advice for one person may be inappropriate or even bad for another, especially where other eye problems are present.
Below are some observations which apply in MOST cases:
- Glasses or contact lenses do not correct nystagmus although they may damp (reduce) CN; they should be worn to correct other vision problems. Vision may vary during the day and is likely to be affected by emotional and physical factors such as stress, tiredness, nervousness or unfamiliar surroundings. Most people with CN and no other visual problems can see well enough to drive a car.
- The angle of vision is important. Most individuals with CN have a null point (a gaze angle where the CN damps); this point can be found and used by looking to one side or the other, where the eye movement is reduced and vision improved. Those with a null point will often adopt a head posture to make best use of their vision. Sitting to one side of a screen, blackboard, etc. does not help because it reduces the angle at which the screen is viewed, causing ‘crowding’. A better solution is to sit directly in front and adopt the preferred head turn or have corrective surgery (or use prisms) to eliminate the head turn.
- Small print. Many can read very small print if it is close enough or with use of a visual aid. However, the option of large print material should be available and all written matter should be clear. It isvery hard to share a book with someone because it will probably be too far away or at the wrong angle.
- Good lighting is important. If in doubt get the advice of a specialist, particularly as some people are also light sensitive. Computers are used by many people with nystagmus, who benefit from them as they can position screens to suit their own needs and adjust brightness, character size etc. However some find it difficult to read computer screens. Reading speed is not usually reduced by nystagmus itself, but by other associated visual deficits. CN should not be taken as a predictor of poor reading.
- Balance can be a problem in acquired nystagmus, which can make it difficult to go up and down stairs. Finally, a widespread lack of understanding of the various types of nystagmus is often as much a source of difficulty as nystagmus itself. We are doing our best to overcome this problem and would be glad if you could help in this aim.
Grateful acknowledgement is made to the Nystagmus Network (U.K.) for permission to use this text, with minor revisions.