Nystagmus

Nystagmus is defined as an involuntary 'to and fro' movement of the eyes in a horizontal, vertical, rotatory or mixed direction. The presence and characteristics of such movements help localise to the site of neurological disease.

Nystagmus may be pendular - equal velocity and amplitude in all directions, or jerk - with a fast phase (specifying the direction) and a slow phase.

The normal maintenance of ocular posture and alignment of the eyes with the environment depends upon:

Retinal input

Labyrinthine input

Retinal input

Labyrinthine input

Cerebral cortex

Central connections in brain stem with vestibular nuclei/cerebellum

Central connections in brain stem with vestibular nuclei/cerebellum

Nystagmus may result from:

- retinal disease

- labyrinthine disease, or

- disorders affecting the cerebellum or a substantial portion of the brain stem. Examination for nystagmus

'Nystagmoid' movements of the eyes are present in many people at extremes of gaze. Nystagmus present with the eyes deviated less than 30 from the midline is abnormal.

When nystagmus is present only with the eyes deviated to one side - 1st degree nystagmus.

With eyes deviated to one side and in the midline position also - 2nd degree nystagmus.

When present in all directions of gaze - 3rd degree nystagmus.

If nystagmus is detected, note the type (jerk or pendular), direction (of fast phase) and degree. Nystagmus suppressed by visual fixation may appear in darkness, but this requires specialised techniques (electronystagmography - see page 62) to demonstrate.

RETINAL OR OCULAR nystagmus

Physiological: following moving objects beyond the limits of gaze - opticokinetic nystagmus.

Pathological: occurs when vision is defective. Fixation is impaired and the eyes vainly search.

Nystagmus is: Rapid

Pendular (lacks slow and fast phase) Increased when looking to sides Persistent throughout lifetime

180 Occurs in congenital cataract, congenital macular defect, albinism.

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