General Information about Nystagmus
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.
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. The flautist James Galway is probably the best known
person with congenital nystagmus.
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
Grateful acknowledgement is made to
the Nystagmus Network (U.K.)
for permission to use this text, with minor revisions.
ANN, Inc. Caveat: Though discussions
on specific problems are permissible and expected, remember that no posting
here shall constitute professional health care or medical advice, and you
should never rely on any contribution to this, or any, Internet discussion
forum on important medical or professional health care questions.
Indeed, no Internet discussion forum is a substitute for the careful advice
and treatment of a competent professional health care provider or doctor.
ANN, Inc. is a volunteer, nonprofit
organization for persons and families involved with nystagmus. ANN, Inc.
does not diagnose or treat, or provide professional counseling. It is involved
in self-help, while trying to promote research and education, among other
goals contained in its mission statement.
Copyright © 1996-2002, American
Nystagmus Network. Last Revised: February 21, 2002.
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