(nis-tag′mŭs)

[Gr. nystagmos, nodding]
Involuntary back-and-forth or cyclical movements of the eyes. The movements may be rotatory, horizontal, or vertical and often are most noticeable when the patient gazes at objects moving by rapidly or at fixed objects in the peripheral field of view.

ETIOLOGY
Lesions of the labyrinth, vestibular nerve, cerebellum, and brainstem commonly produce rhythmic eye movements. Drug intoxications, e.g., with alcohol or phenytoin, also may be responsible.

aural nystagmus

Nystagmus due to a disorder in the labyrinth of the ear. Eye movement is spasmodic.

bidirectional nystagmus

Nystagmus that occurs both to the left and the right, or up and down. It is a characteristic of a central nervous system lesion.

Cheyne nystagmus

SEE: Cheyne nystagmus

convergence nystagmus

Slow abduction of eyes followed by rapid adduction.

dissociated nystagmus

Nystagmus in one eye that is not synchronized with that in the other eye.

end-position nystagmus

Nystagmus that occurs when eyes are turned to extreme positions. It may occur normally in debilitation or fatigue, or it may be due to pathology of the subcortical centers for conjugate gaze. VAR: end-point nystagmus.

fixation nystagmus

Nystagmus that occurs only when the eyes gaze at an object.

gaze-evoked nystagmus

Nystagmus upon holding the eyes in an eccentric position. It is due to dysfunction of the brainstem, or it may be caused by drugs such as sedatives or anticonvulsants. The direction of the nystagmus may change when the individual is fatigued or returns fixation to the primary position. This is called rebound nystagmus.

induced nystagmus

Nystagmus that results from active examination of the patient, e.g., while turning the patient's head.

jerk nystagmus

SEE: Rhythmic nystagmus.

labyrinthine nystagmus

Nystagmus due to disease of the labyrinthine vestibular apparatus.

latent nystagmus

Nystagmus that occurs only when one eye is covered.

lateral nystagmus

Horizontal movement of the eyes from side to side.

manifest nystagmus

Nystagmus present at all times whether or not one's gaze is directed toward a visual stimulus.

miner's nystagmus

Nystagmus occurring in those who work in comparative darkness for long periods.

opticokinetic nystagmus

A rhythmic jerk nystagmus occurring when one is looking at constantly moving objects, e.g., viewing telephone poles from a moving car or train.

paretic nystagmus

Weakness of the extraocular muscles that produces abnormal eye movement, either side to side or up and down.

pendular nystagmus

Nystagmus characterized by movement that is approx. equal in both directions. It is usually seen in those who have bilateral congenital absence of central vision or who lost it before the age of 2.

positional nystagmus

Nystagmus induced by a change in the position of one's head.

postrotatory nystagmus

A form of vestibular nystagmus that occurs when the body is rotated and then the rotation is stopped. If, while sitting upright in a chair that can be swiveled, the body is rapidly rotated to the right, the nystagmus during rotation has its slow component to the left. When the rotation stops, the slow component is to the right. Stimulation of the semicircular canals causes this type of nystagmus, and it is a normal reaction.

rebound nystagmus

SEE: gaze-evoked nystagmus

retraction nystagmus

Nystagmus associated with the drawing of the eye backward into the orbit.

rhythmic nystagmus

Nystagmus in which the eyes move slowly in one direction and then jerk back rapidly.
SYN: SEE: jerk nystagmus

rotatory nystagmus

Nystagmus in which eyes rotate about the visual axis. VAR: torsional nystagmus.

seesaw nystagmus

Nystagmus in which the inturning eye moves up and the opposite eye moves down, and then both eyes move in the opposite direction.

spontaneous nystagmus

Nystagmus present when one's head is still. It is often caused by an acute vestibular disease and usually resolves within seven days.

vertical nystagmus

Involuntary up-and-down ocular movements.

vestibular nystagmus

Nystagmus caused by disease of the vestibular apparatus of the ear or due to normal stimuli produced when the semicircular canals are tested by rotating the body.
SEE: postrotatory nystagmus

voluntary nystagmus

A rare type of pendular nystagmus in those who have learned to oscillate their eyes rapidly, usually by extreme convergence.