Diabetic retinopathy is the leading cause of new cases of blindness in the western world. Inflammation and hypoxia are thought to play a significant role in the pathogenesis of retinopathy; however, the mechanisms remain unclear. A potential mechanism for the development of retinopathy is a decrease in retinal blood flow (possibly mediated by thromboxane, TxA₂) leading to an increase in hypoxia and the hypoxia transcription factors HIF-1α and HIF-2α. Mice and rats were injected with streptozotocin (STZ) to render the rodents hyperglycemic and citrate buffer for control. At early time points following induction of hyperglycemia, retinal arteriolar and venular diameters, velocity of blood, and retinal blood flow were measured using intravital microscopy. Immunofluorescent labeling was used to quantify changes in thromboxane synthase (TxS), the enzyme responsible for converting prostaglandin H ₂ to TxA₂ in the arachidonic acid pathway, and its receptor the thromboxane-prostanoid (TP) receptor. The transcription factors HIF-1α and HIF-2α were quantified using immunofluorescent labeling. Following four weeks of hyperglycemia in STZ-injected mice, retinal arteriolar diameters, velocity, and flow were decreased. The decrease in arteriolar diameter was attenuated following an acute infusion of Ozagrel, a thromboxane synthase inhibitor and Vapiprost, a thromboxane receptor antagonist. Total retinal blood was decreased following four weeks of hyperglycemia. This decrease in total retinal blood flow was attenuated following three weeks of daily treatment with vapiprost. Despite the apparent role for thromboxane in decreasing retinal arteriolar diameters and flow, there was no difference in TxS staining between control and STZ-injected mice or rats following four weeks of hyperglycemia. There was no difference in the TP receptor in mice but there was a trend towards an increase in the TP receptor staining in rats in the photoreceptor inner segment. There was no increase in HIF-1α or HIF-2α following four weeks of hyperglycemia in mice or rats. In conclusion, early decreases in retinal arteriolar blood flow are attenuated by thromboxane receptor antagonism. The early decreases in retinal blood flow do not induce up-regulation of hypoxia-induced transcription factors following four weeks of hyperglycemia.