Nystagmus

[Guest guest]

Nystagmus is characterized by an involuntary movement of the eyes, which may

reduce vision or be associated with other, more serious, conditions that

limit vision. Nystagmus may be one of several infantile types or may be

acquired later in life.

The most common types of infantile nystagmus are 'congenital nystagmus' (CN)

and latent/manifest latent nystagmus (LMLN). Many people with CN are also

partially sighted; some are registered blind; few of these can drive a car,

most encounter some difficulties in everyday life -- both practical and

social -- and some lose out on education and employment opportunities.

However, CN or LMLN by themselves do not necessarily reduce acuity

substantially and 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.

There are many types of adult-onset acquired nystagmus. 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

and always acccompanies LMLN. 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.

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.

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.

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.

For more information:

http://www.nystagmus.org/ (in the US)

http://www.nystagmusnet.org/ (in the UK)

http://www.cnib.ca/ (in Canada)

http://www.visinfo.dk/ (in Denmark)

http://www.rvib.org.au/ (in Australia)

http://www.rnzfb.org.nz/ (in New Zealand)