Transient monocular blindness
Temporary loss of vision in one eye, termed transient monocular blindness (TMB), is the most important visual symptom of arteriosclerotic vascular disease, arteritis and states of altered coagulability, and thrombocytosis. In most patients, the visual disturbance during each individual attack of TMB is stereotypic. It may recur over a period of months or over a much briefer span of hours, days, or weeks. A meticulous history of the attack and duration of the visual disturbance will permit classification of the TMB occurrence into one of four types. Type I is due to transient retinal ischemia, type II to retinal vascular insufficiency and type III to vasospasm. Type IV occurs in association with antiphospholipid antibodies but includes cases of unknown etiology (Table 9.1 (Wray, 1988; Burde, 1989)).
TMB type I
TMB type I is characterized by a sudden, brief attack of partial or complete dimming or obscuration of vision, lasting seconds to minutes, followed by total recovery. Partial impairment is described as a greyout, or as an ascending or descending curtain or a blind moving sideways across the eye. Occasionally, the patient will describe moving tracks of light. Ipsilateral headache is rare (Wilson et al., 1979). Fisher (1952) drew attention to the association of TMB of this brevity with contralateral hemiplegia. Episodic attacks of fleeting blindness occur as arteriosclerotic plaques progressively narrow the lumen of the ipsilateral internal carotid artery (ICA), leading to periodic reduction in blood flow, reduced pressure in the ophthalmic artery, transient ocular ischemia, or vascular insufficiency.