Nystagmus

Nystagmus is rapid involuntary rhythmic eye movement, with the eyes moving quickly in one direction (quick phase), and then slowly in the other (slow phase). The direction of nystagmus is defined by the direction of its quick phase (e.g., right nystagmus is due to a right moving quick phase). Nystagmus may occur in the vertical or horizontal directions, and also in a semicircular movement, and thus are called downbeat nystagmus, upbeat nystagmus, seesaw nystagmus, periodic alternating nystagmus, and pendular nystagmus. There are other similar alterations in periodic eye movements (saccadic oscillations) such as opsoclonus or ocular flutter. One can accurately think of nystagmus as the combination of a slow adjusting eye movement (slow phase) like would be seen with the vestibulo-ocular reflex, followed by a quick saccade (quick phase) when the eye has reached the limit of its rotation.

Related Topics:
Eye movement - Opsoclonus - Ocular flutter - Vestibulo-ocular reflex - Saccade

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In medicine, the clinical importance of nystagmus is that it indicates that the patient's spatial sensory system perceives rotation and is rotating the eyes to adjust. Thus it depends on the coordination of activities between two major physiological systems: the vision and the vestibular apparatus (which controls posture and balance). This may be physiological (or normal) or pathological.

Related Topics:
Medicine - Vision - Vestibular apparatus - Posture - Balance - Physiological - Pathological

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An easy way of inducing physiological nystagmus is by having the person close her or his eyes and spin around. After a few spins, there is a distinct jerking of the eyes from side to side when they are reopened: this is rotatory-induced nystagmus. Strobe lights also produce nystagmus. The degree of physiological nystagmus varies greatly between people and even in the same person at different times. Another type of physiological nystagmus is the optokinetic nystagmus (OKN). It can be induced by presenting a moving pattern. The eyes tend to track the pattern, but snap back regularly. Nystagmus is distinguished from normal involuntary eye activity by the rapidity and repetitive pattern of the movement.

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