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    The trypsin digest—a light microscopic study of retinal blood vessels—on the right highlights an early change of diabetic retinopathy: loss of pericytes, the supportive cells of the retinal vasculature, which are more numerous in the normal digest on the left. Endothelial cells are lost later. These abnormalities are followed by the formation of microaneurysms, leaky outpouchings of the capillary walls that represent the first clinically detectable evidence of diabetic retinopathy. Other sequelae include abnormal permeability, capillary nonperfusion, and neovascularization.