Measurement Of Retinal Blood Flow Rate In Diabetic Rats: Disparity Between Techniques Due To Shunting Of Capillary Flow

The objective of this study was to clarify whether retinal blood flow (RBF) rates are altered in rats during streptozotocin (STZ)‐induced diabetes. Reports of this possibility in the literature are mixed, possibly due to the different techniques used to measure RBF. STZ (or vehicle alone, in controls) was injected into the rats (30 mg/kg for 3 days) to induce a model of type I diabetes. Eight weeks later, RBF rates were measured in the anesthetized rats using intravital microscopy and a fluorescent tracer (FITC‐dextran) in a mean circulation (transit) time index of flow. In separate rats, RBF was measured using a microsphere infusion technique. The induction of diabetes resulted in a 30–35% decrease in RBF (***p<0.001) in the STZ rats as determined by the microsphere measurement. However, in a striking contrast to these results, the mean transit times of injected FITC‐dextran were ~3× faster in the STZ rats compared with the controls (**p<0.01). We hypothesize that this discrepancy is due to shunting of RBF away from the deep retinal capillary layers in the STZ rats, with the altered flow pattern allowing the rapid transit of tracer from the arterioles into the venules. Funded by NIH EY017599 (NRH).