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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. Most frequently it is composed of a mixture of slow and fast movements
of the eyes. Nystagmus can occur normally, such as when tracking a visual
pattern. Nystagmus may also be abnormal, usually in situations where one would
want the eyes to be still, but they are in motion.
The involuntary eye movements of nystagmus are caused by abnormal function in
the areas of the brain that control eye movements. The exact nature of these
disorders is poorly understood.
Muscles of the eye
There are six muscles that control the movement of each eye ball. The image
shows the six muscles of the right eye.
Nystagmus may be either congenital (present at birth) or may be acquired
(caused by disease or injury later in life).
Congenital Nystagmus:
It is the most common. It is usually mild, does not change in severity, and is
not associated with any other disorder. Affected people are not aware of the eye
movements, although they may be noticed by a careful observer. If the movements
are of large amplitude, visual acuity (sharpness of vision) may be less than
20/20. Surgery may improve visual acuity.
Acquired Nystagmus: A less common cause of nystagmus is disease or
injury of the central nervous system. The most common cause of acquired
nystagmus is head injury from motor vehicle accidents in young people. In older
people the most common cause is
stroke (blood vessel blockage in the brain). Any disease of the brain (such
as
multiple sclerosis or brain tumors) can cause nystagmus if the areas
controlling eye movements are damaged. Because control of eye movements is
affected by input from the labyrinth (the part of the inner ear that senses
movement and position), inner ear disorders (such as Meniere's disease) can also
lead to acquired nystagmus. Other causes include Dilantin (an antiseizure
medication), toxicity, and alcohol intoxication.
Nystagmus can be classified depending upon the type of motion of the eyes.
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In pendular nystagmus the speed of motion of the eyes is the same
in both directions.
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In jerk nystagmus there is a slow and fast phase. The eyes move
slowly in one direction and then seem to jerk back in the other direction.
"Rule" for
Sensory (Pendular) Nystagmus
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Vision loss
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Nystagmus
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Before 2 years*
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Always
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Before 4 years
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Often
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After 6 years
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Never
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* This nystagmus
is not present at birth but develops by approximately 6 months.
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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.
There are many causes of nystagmus. Nystagmus may be present at birth. It may be
a result of the lack of development of normal binocular fixation early on in
life. This can occur if there is a cataract at birth or a problem is some other
part of the visual system.
Some other conditions that nystagmus may be associated with include:
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Albinism. This condition is caused by a decrease in pigmentation and
may affect the eyes.
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Disorders of the eyes. This may include optic atrophy, color
blindness, very high nearsightedness (myopia) or severe astigmatism, or
opacities in the structures of the eyes.
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Acute labyrinthitis. This is an inflammation in the inner ear.
The patient may have dizziness (vertigo), nausea and vomiting, and nystagmus.
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Brain lesions. Disease in many parts of the brain can result in
nystagmus.
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Alcohol and drugs. Alcohol and some medications (e.g.,
anti-epilepsy medications) can induce or exaggerate nystagmus.
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Multiple sclerosis. A disease of the central nervous system.
Nystagmus can run
in families, and it has been known to be passed down to the next
generation, but can also skip generations.
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Diagnosis is made clinically based on the medical history and physical
examination.
Diagnostic tests that may be performed include:
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CT scan of the head or MRI of the head
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Electro-oculography: An electrical method of measuring eye movements
using tiny electrodes.
 Motion
sickness medicines sometimes help. But the reaction will dissipate if
continuously evoked. Each morning a patient is asked to produce the symptom by
moving his or her head around until it no longer happens. This prevents it from
returning for several hours or the entire day.
Prisms, contact lenses, eyeglasses, or eye muscle surgery are some
possible treatments. These therapies may reduce the nystagmus but may not
alleviate it. Again, because nystagmus may be a symptom, it is important to
determine the cause.
 Adjunctive
therapeutic modes (e.g., Fresnel prisms (Prisms that make up a Fresnel lens bend
and magnify light rays, creating a single, concentrated beam of light) and
orthoptic (Orthoptics refers to how well the two eyes work together as a team)
exercises) can also be beneficial. PAN and see-saw nystagmus can be treated with
baclofen. Downbeat nystagmus may respond to clonazepam therapy, and prisms may
help if the nystagmus can be modified with convergence. Congenital nystagmus may
respond minimally to drugs (e.g., baclofen), but prisms or surgical procedures,
or both, are still the primary treatment modalities.
Near Point of
Convergence Exercises:
�An accommodative target, such as the point of a pencil (i.e.,
pencil push-ups), is placed remote to the patient�s near point of
convergence and gradually brought toward the tip of the nose with
the patient converging to avoid diplopia. Just before there is a
break in fusion, the patient holds fixation the target for 10
seconds. This so-called push-up is repeated 10 times, 2-4 times a
day, until the patient is able to hold fixation to the tip of the
nose. The exercises can be tapered and then used on an as-needed
basis when the patient notices a recurrence of symptoms.�
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Diet and Nystagmus
Two case reports illustrate the therapeutic response of congenital nystagmus to
a diet eliminating synthetic food colors, synthetic food flavors, the
antioxidant preservatives butylated hydroxytoluene (BHT) and butylated
hydroxyanisole (BHA), and a small group of foods thought to contain a natural
salicylate radical. For more.
click here
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