Cranial Nerves: Nystagmus

Published on 09/04/2015 by admin

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Last modified 22/04/2025

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Cranial Nerves

Nystagmus

BACKGROUND

Nystagmus is an oscillation of the eyes. This can be a symmetrical oscillation—pendular nystagmus—or faster in one direction—jerk nystagmus. In jerk nystagmus there is a slow drift in one direction with a fast correction in the opposite direction. It is conventional to describe the nystagmus in the direction of the fast phase. If the oscillation is a twisting movement, this is torsional or rotatory nystagmus.

Nystagmus can be:

• physiological: oculokinetic nystagmus (as seen in people looking out of the windows of trains)

• peripheral: due to abnormalities of the vestibular system in the ear, the eighth nerve nucleus or the nerve itself

• central: due to abnormalities of the central vestibular connections or cerebellum

• retinal: due to the inability to fixate.

WHAT TO DO

Ask the patient to follow your finger with both eyes. Move the finger in turn up, down and to each side. Hold the finger briefly in each position at a point where the finger can easily be seen by both eyes.

Watch for nystagmus. Note:

• whether it is symmetrical, moving at the same speed in both directions (pendular nystagmus), or if there is a fast phase in one direction with a slow phase in the other (jerk nystagmus)

• the direction of the fast phase—is it in the horizontal plane, in the vertical plane or rotatory?

• the position of the eye when nystagmus occurs and when it is most marked

• whether it occurs only towards the direction of gaze (first degree), in the primary position of gaze (second degree) and whether it occurs with the fast phase going away from the direction of gaze (third degree)

• whether it affects the abducting eye more than the adducting eye

• whether it occurs in one direction only

• whether it occurs in the direction of gaze in more than one direction (multidirectional gaze-evoked nystagmus).

To decide whether it is central or peripheral, note:

• whether it persists or fatigues

• whether it is associated with a feeling of vertigo

• whether it improves with visual fixation.

COMMON MISTAKES

• At the extreme of lateral gaze, one or two nystagmoid jerks can be seen normally, especially if the target is too close—ensure that the target remains within binocular vision.

• If nystagmoid jerks are found, repeat the test. If this is true nystagmus, it will appear at less than extreme lateral gaze.

Special test: optokinetic nystagmus (OKN)

This can be tested when a striped drum is spun in front of the eyes; this normally evokes nystagmus in the opposite direction to the direction of spin. This is a useful test for patients with hysterical blindness.

Tests for benign positional vertigo are described in Chapter 12.