EVOKED NYSTAGMUS

Timothy C. Hain, MD

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Nystagmus is defined as involuntary movement of the eyes. Most frequently it is composed of a mixture of slow and fast movements of the eyes. Nystagmus can occur normally, such as when tracking a visual pattern. Nystagmus may also be abnormal, usually in situations where one would want the eyes to be still, but they are in motion. Vertigo (a sensation of spinning), is often accompanied by nystagmus.

Evoked nystagmus is nystagmus that is caused by a particular maneuver such as looking to one side (gaze evoked nystagmus), turning the head back and forth (head-shaking nystagmus), etc. These are the types that are covered primarily on associated pages.

GAZE EVOKED NYSTAGMUS

Gaze-evoked nystagmus is the nystagmus that is provoked by particular directions of gaze. See this page for more information.

Head-shaking Nystagmus

Head-shaking nystagmus is the nystagmus evoked by moving the head sinusoidally, typically for 20 cycles. See this page for more information.

Hyperventilation Induced Nystagmus (see here for more detail)

Hyperventilation induced nystagmus has been reported in patients with acoustic neuroma and other CP angle tumors, in microvascular compression, in perilymph fistula, and in patients with MS and patients with cerebellar dysfunction. In hyperventilation induced nystagmus, the nystagmus beats towards the lesion. This is opposite to the direction of vibration induced nystagmus.

Reference:

Supplemental material : Video of hyperventilation induced nystagmus in person with right sided acoustic neuroma

Caloric nystagmus

Caloric nystagmus is a vestibular nystagmus induced by a temperature differential across a semicircular canal, that is not perpendicular to the gravitational axis. Caloric testing is routinely used to evaluate vestibular function. See this page for more information.

Optokinetic nystamus (OKN) testing and OKAN


In optokinetic testing a large pattern is rotated around the subject or a handheld drum is used to evoke pursuit. OKN is much less useful than is rotatory chair testing as it is rarely affected substantially by disease. Optokinetic afternystagmus (OKAN) describes the eye movements that occur after the lights are turned out for OKN, and the subject is in complete darkness. OKAN is only elicited by large field stimuli. OKAN is more sensitive to disease than OKN, but it is variable in normal subjects, which again limits its usefulness.

References:

Vibration Induced Nystagmus (follow link for much more)

Under video Frenzel goggles, it is common to see nystagmus provoked by vibration over the ears, over the front or back of the neck. This nystagmus is presently under investigation by several groups. In persons with unilateral vestibular loss, a nystagmus occurs nearly 100% of the time on vibration over the sternocleidomastoid muscles, with slow-phases directed toward the side of lesion. While the slow-phase velocity may not be very high, the nystagmus can easily be seen as being different from normal fixation behavior. In many normal individuals nystagmus is produced that beats to the left on stimulation of the left side and to the right on the right side. This is not associated with any known pathology.

Hamman KF, Schuster EM. Vibration-induced nystagmus -- A sign of unilateral vestibular deficit. ORL J. 1999 Mar-Apr 61(2) 74-9

Positional Nystagmus

There are many subvarieties of positional nystagmus --

An attempt to provide a differential diagnosis for positional nystagmus is found here.