Nystagmus is a rhythmic oscillation ofthe eyes, analogous to a tremor in other parts of the body. Its causes are multiple, including impairment of vision in early life, disorders ofthe labyrinth and the cerebellar system, and drug toxicity. Nystagmus oc-
Direction of the Quick and Slow Components
Example: Nystagmus to the Left—A Slow Drift to the Right, Then a Quick Jerk to the Left in Each Eye
o curs normally when a person watches a rapidly moving object (e.g., a passing train). Observe the three characteristics of nystagmus listed below and on the following page. Then refer to textbooks of neurology for differential diagnosis.
Nystagmus usually has both fast and slow movements, but is defined by its fast phase. For example, if the eyes jerk quickly to the patient's left and drift back slowly to the right, the patient is said to have nystagmus to the left.
Occasionally, nystagmus consists only of coarse oscillations without quick and slow components. It is then said to be pendular.
The movements of nystagmus may occur in one or more planes (i.e., horizontal, vertical, or rotary). It is the plane of the movements, not the direction of the gaze, that defines this variable.
Direction of Gaze in Which Nystagmus Appears
Example: Nystagmus on Right Lateral Gaze
Nystagmus Present (Right Lateral Gaze)
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