Nystagmus is a term to describe fast, uncontrollable movements of the eyes that may be:
- Side to side (Horizontal Nystagmus)
- Up and down (Vertical Nystagmus)
- Rotary (Rotary or Torsional Nystagmus)
Depending on the cause, these movements may be in both eyes or in just one eye. The term "dancing eyes" has been used 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 part of the inner ear that senses movement and position (the labyrinth) helps control eye movements.
There are two forms of nystagmus:
- Infantile nystagmus syndrome (INS) is congenital.
- Acquired nystagmus develops later in life because of a disease or injury.
The cause for pathological nystagmus may be congenital, idiopathic, or secondary to a pre-existing neurological disorder. It also may be induced temporarily by disorientation (such as on roller coaster rides) or by certain drugs (alcohol and other central nervous system depressants, inhalant drugs, and stimulants).