Episodic Disorders of Vision

Introduction. Of all our senses, vision is most commonly associated with patient distress, if not overt alarm, when abruptly compromised. Despite patient concern, a rare, or rarely recognizable, clinical entity is perhaps of less significance to the physician than to the patient. When the broad spectrum of episodic disturbance of vision is closely examined, it becomes apparent that these visual symptoms are indeed of common occurrence in the population at large. Surprisingly, despite their ultimate effect on the eye, a majority of the clinical entities that produce episodic disturbance of vision are neurologic (Fig 1 ). Episodic is defined as being " ... made up of separate, loosely connected episodes."* In turn, an episode is " .. . a usually brief unit of action ... an occurrence or connected series of occurrences and developments which may be viewed as distinctive and apart, although part of a larger or more comprehensive series ."* In binocular man, episodic visual change has two essential parameters of basic diagnostic significance: Time and laterality. In terms of time, an episode has both duration and frequency. Although both characteristics are of diagnostic value, duration is the one most frequently used in discussing disorders of vision. Episodes may vary in duration from seconds to as long as months (Fig I). A no less important element is the laterality of