Retinal blood flow in normal and diabetic dogs.

We have found retinal blood flow to be decreased in diabetic dogs 5 months after the onset of diabetes, which is long before they can be expected to develop morphological changes of diabetic retinopathy. Retinal blood flow was determined using radionuclide labelled microspheres. In eight alloxan diabetic dogs without retinopathy, the retinal blood flow was 0.53 +/- 0.08 (mean +/- SE) ml/min/gm dry tissue weight. This compares with 0.91 +/- 0.17 (mean +/- SE) ml/min/gm dry tissue weight in seven normal dogs. The decreased blood flow in diabetic retinas is statistically significant (P = 0.05). Blood glucose levels did not significantly affect retinal blood flow. This data suggest that changes in retinal blood flow and oxidative metabolism may precede the morphological signs of diabetic retinopathy.