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Abstract
The ultrastructure of old neovascular preretinal membranes was examined in both eyes of a patient with proliferative diabetic retinopathy treated in one eye with photocoagulation. Membranes in both eyes consisted of a matrix rich in mature collagen surrounding viable new vessels and "ghost vessels." Viable vessels of different calibers frequently showed endothelial fenestrae bridged by diaphragms. Occasionally tight junctions between endothelial cells appeared altered. Fenestrae and incompetent junctions may account for the characteristic "leakiness" of newly formed vessels.