SUMMARY As diabetic retinopathy progresses, the non-perfused area in the retina gradually enlarges as the capillaries are obstructed. To elucidate the process of capillary obstruction we examined macular capillaries in 104 diabetics, using fluorescein angiography. The follow-up period was three to eight years. We found that some capillaries in the macula were obstructed, then became unobstructed. Reflow of blood into the macula after the obstruction was observed in nine patients (8.7%). The time between obstruction and reflow varied from two months to four years. There were four cases of simple, three of preproliferative, and two of proliferative retinopathy. Reflow in the capillaries was confirmed as occurring at the same position and in vessels with the same diameter as seen before the obstruction. There was no leakage of the fluorescein dye from the capillary where reflow took place. We tentatively conclude that one of the causes of this phenomenon is a functional obstruction.It is generally accepted that diabetic retinopathy is a form of microangiopathy. As the retinopathy progresses, the non-perfused area in the retina gradually enlarges as a result of obstruction of the capillaries.Although several ophthalmologists reported this phenomenon, each report was of one case and the state of the capillaries before the obstruction was not described.'" Almost all reported that this phenomenon occurred after photocoagulation. We therefore examined the occurrence rate of the reflow of the obstructed capillaries, the type of capillary reflow, and the possible relation to photocoagulation. Subjects and methodsFluorescein angiography was carried out from 1977 to 1985 on 104 eyes of 104 diabetics aged 16 to 78 years. All were treated by diabetologists and the follow-up was for three to eight years. Thirty were cases of insulin-dependent diabetes mellitus (IDDM) and 74 of non-insulin-dependent diabetes mellitus (NIDDM). Diabetics without retinopathy, deterCorrcspondcncc to Yasuo Yamana. MD, Yamana Eye Clinic, 10-Nabeyama Nakama-shi Fukuoka, 809 Japan. mined by ophthalmoscopy, numbered 22. In 58 cases there was a simple retinopathy, 18 had a preproliferative retinopathy, and six a proliferative retinopathy.All patients were examined by ophthalmoscopy after the pupil had been dilated with 10% phenylephrine and 0-5% cyclopentolate. Fluorescein fundus angiography and colour photography were carried out periodically, the frequency depending on the severity of the diabetic retinopathy. 5 ml of 10% sodium fluorescein was given intravenously.We examined coagulation and platelet aggregation at the time of occlusion, and adenosine-5'-diphosphate (ADP) and coagulation were examined at the time of occlusion and after reflow in patient 1 and after reflow in eight patients.