Autoregulation of retinal blood flow in diabetic retinopathy measured by the blue-light entoptic technique.

Autoregulation of retinal blood flow was measured in 23 diabetic patients, 9 with nonproliferative retinopathy, 9 with proliferative retinopathy, and 5 with photocoagulated retinopathy. Three of the proliferative patients were studied on two occasions, at the proliferative stage and after photocoagulation. The stimuli to autoregulation used were isocapnic hyperoxia and hypoxia. Flow velocity of leukocytes in the perifoveal circulation was measured using the blue-field entoptic technique, and retinal artery and vein diameters were measured using a computerized digitizing system. Results under conditions of isocapnic hypoxia showed a mean increase in flow velocity of 41.0 +/- 33.0% (P less than 0.05) in nonproliferative retinopathy, 3.5 +/- 17.0% (not significant) in proliferative retinopathy, and 30.0 +/- 17.0% (P less than 0.05) after photocoagulation. In hyperoxia, flow velocity fell by a mean of 21.0 +/- 21.6% (P less than 0.05) in nonproliferative retinopathy, 33.0 +/- 19.9% (P less than 0.005) in proliferative retinopathy, and 21.0 +/- 26.0% (not significant) in photocoagulated retinopathy. The results are compared with a group of nondiabetic subjects reported previously.