Sudden transitory impairment, or loss, of vision. It usually aﬀects only one eye, and is commonly due to circulatory failure. In its simplest form it occurs in normal people on rising suddenly from the sitting or recumbent position, when it is due to the eﬀects of gravity. It also occurs in migraine. A not uncommon cause, particularly in elderly people, is transient ocular ISCHAEMIA, resulting from blockage of the circulation to the retina (see EYE) by emboli (see EMBOLISM) from the common carotid artery or the heart. Treatment in this last group of cases consists of control of the blood pressure if this is raised, as it often is in such cases; and the administration of drugs that reduce the stickiness of blood platelets, such as aspirin. In some instances, removal of the part of the carotid artery from which the emboli are coming may be indicated.
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