Nystagmus refers to rapid involuntary movements of the eyes that may be:

• Side to side (horizontal nystagmus)
• Up and down (vertical nystagmus)
• Rotary

Depending on the cause, these movements may be in both eyes or in just one eye. The term "dancing eyes" has been used in regional dialect to describe nystagmus.

Uncontrollable eye movements are involuntary, rapid, and repetitive movement of the eyes.

The involuntary eye movements of nystagmus are caused by abnormal function in the areas of the brain that control eye movements. The part of the inner ear that senses movement and position (the labyrinth) helps control eye movements.

The exact nature of these disorders is poorly understood.

There are two forms of nystagmus:

• Congenital nystagmus is present at birth. This is the most common type.
• Acquired nystagmus develops later in life because of a disease or injury.

CONGENITAL NYSTAGMUS

Congenital nystagmus 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 magnitude, visual acuity (sharpness of vision) may be less than 20/20. Surgery may improve visual acuity.

Rarely, nystagmus occurs as a result of congenital diseases of the eye that cause poor vision. Although this is rare, an ophthalmologist should evaluate any child with nystagmus to check for eye disease.

ACQUIRED NYSTAGMUS

Inner ear disorders such as labyrinthitis or Meniere's disease can lead to acquired nystagmus. However, the most common cause is probably toxic -- certain drugs or medication, including Dilantin (an antiseizure medication), alcohol intoxication, or any sedating medicines can harm the labyrinth.

In young people, a common, serious cause of acquired nystagmus is head injury from motor vehicle accidents.

In older people, a common, serious 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.

There is no therapy for most cases of congenital nystagmus. Availability of treatment for acquired nystagmus will vary with the cause. In most cases, except for those caused by Dilantin or alcohol intoxication, nystagmus is irreversible.

Call your health care provider if nystagmus is detected or suspected.

Nystagmus may be observed through the following procedure: If the affected person spins around for about 30 seconds, stops, and tries to stare at an object, the eyes will first move slowly in one direction, then move rapidly in the opposite direction. If you have nystagmus due to a medical condition, these eye movements depend on the underyling cause.

Your health care provider will take a careful history and perform a thorough physical examination, which will emphasize the nervous system and inner ear. The doctor may ask you to wear a pair of goggles that magnify the eyes for part of the neurological examination.

Questions asked in a medical history may cover the following areas:

• When was it first noticed?
• How often does it occur?
• Has it ever happened before?
• Is it getting better, worse, or staying the same?
• Are there side-to-side eye movements?
• Are there up-and-down eye movements?
• What medications are being taken?
• What other symptoms are present?

Diagnostic tests that may be performed include:

• CT scan of the head or MRI of the head
• Electro-oculography: An electrical method of measuring eye movements using tiny electrodes.
• Vestibular testing – recording the movements of the eyes and response to caloric stimulation

There is no therapy for most cases of congenital nystagmus. Treatment for acquired nystagmus depends on the cause. In some cases, nystagmus is irreversible. In cases due to medications or infection, the nystagmus usually goes away after the initial cause has resolved.

Baloh R. Neuro-ophthalmology. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 450.

Goodwin J. Cranial nerves III, IV, and VI: The oculomotor system. In: Goetz, CG, ed. Textbook of Clinical Neurology. 3rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 9.