The natural history of the first clinically visible features of diabetic retinopathy.

Microaneurysms are the first features of human diabetic retinopathy that can be detected with common clinical techniques. These are found, most often, in photographic field 2 (that is, an area occupying 30 degrees of the ocular fundus centered on the middle of the macula). After the first microaneurysms develop, there will be a tendency for more to appear; however, over time many of the original microaneurysms will become no longer visible with clinical techniques, while other, newer, microaneurysms mature. After the onset of microaneurysms, several years may pass before any other diabetic retinopathic lesions develop. Lesions other than microaneurysms were uncommon in this study; the following is a list in decreasing frequency: retinal hemorrhages, soft exudates, IRMA, hard exudates, and venous beading. During the 4 years of this study, there were no other diabetic retinopathic lesions detected. The duration of insulin-dependent diabetes mellitus was related to the rate of change in microaneurysm counts. The age and sex of patients did not affect this rate of change. The accuracy of metabolic control, as determined by glycosylated hemoglobin levels, may influence this rate of change; however, this was detected only at the extremes of measurement in this study. The equipment available to most ophthalmologists can detect the earliest clinical aspects of diabetic retinopathy. These features can be quantified in a reproducible manner with standardized photographic techniques to permit satisfactory data analysis.