Small, involuntary jerky movements of tremors of the eyes. Everyone shows such movements to some extent, but it is usually considered to be abnormal when it occurs spontaneously. Vertical nystagmus, which occurs much less frequently than horizontal nystagmus, can be a sign of serious brain damage. Railway or optokinetic nystagmus occurs when a person is on a moving train and looking at a stationary object, and the eyes follow the object and then jerk back to start again. This type of nystagmus is used to test vision and balance or postural control in young infants. Post-rotational nystagmus occurs when there are large, slow eye movements sustained in the opposite direction to that of the (rapid) rotation after it is stopped. Once again, this is used to test young infants, but now to evaluate the integrity of the vestibular system.
See Eye movements, Medulloblastoma, Postural control, Vestibular system