Nystagmus refers to rapid involuntary movements of the eyes that may be from side to side (horizontal nystagmus), up and down (vertical nystagmus) or 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.
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. Nystagmus may be either congenital (present at birth) or may be acquired (caused by disease or injury later in life).
CONGENITAL NYSTAGMUS
Congenital nystagmus is more common than acquired nystagmus. 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 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 this.
ACQUIRED NYSTAGMUS
A less common cause of nystagmus is disease or injury of the central nervous system.
In young people the most common cause of acquired nystagmus is head injury from motor vehicle accidents. 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 may include Dilantin (an antiseizure medication) or alcohol intoxication.
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. The orientation of these alternating movements (side to side, up and down, or in a circular pattern) depends on the type of nystagmus.
