INTRODUCTION TEMPORARY obscuration of vision, unilateral or bilateral is not uncommon, especially if under that heading one includes the transient amaurosis associated with spasm of accommodation, glaucoma, and hysteria. The visual disturbance accompanying migraine is another common example. Rarer causes of intermittent blindness include eclampsia, lead poisoning, ergot poisoning, malaria, quinine and tobacco intoxication, polycythaemia rubra vera, and paroxysmal hemoglobinuria. Circulatory deficiency in the territory of the basilar and posterior cerebral arteries may also occasion transient disturbances in vision. The bizarre, rapidly changing field defects complained of in the presence of papilledema, particularly when it is due to intracranial venous thrombosis, are less well known. In addition to the above types, however, there is a fairly large number of cases of periodic blindness in which the principal derangement is an interruption of the retinal blood flow, usually of one eye only. It is this group of cases which is under
M. Fisher (Fri,) studied this question.