Involuntary rhythmic movements of the eyes. Most commonly, movements consist of a slow movement of both eyes in one direction, followed by a fast corrective movement (a jerk) in the opposite direction. Nystagmus can be either a sign of disease in eye movement pathways (in brainstem or cerebellum) or a normal physiological response to certain stimuli like rotation of the body. See caloric nystagmus, optokinetic nystagmus and postrotational nystagmus.