This is an involuntary rapid tracking movement of the eyes. It usually affects both eyes, and is often exaggerated or stopped by looking in a particular direction.

The eyes may move from side to side (horizontal nystagmus), up and down (vertical nystagmus), circular (rotatory nystagmus) or a combination of these.

The most common types are motor and sensory nystagmus:

• Motor nystagmus is usually hereditary and present shortly after birth
• Sensory nystagmus is an acquired condition usually beginning in infancy

If the underlying cause is known it may be treatable.