Blood flow after retinal ischemia in cats.

PURPOSE To determine the changes in blood flow in the cat retina after 1 hour of ischemia. METHODS Blood flow in the retina and choroid of adult cats anesthetized with chloralose, acepromazine, and halothane was measured using sequential injections of radioactively labeled microspheres. Ischemia was induced by elevation of intraocular pressure above systolic arterial pressure. Measurements were carried out before (baseline) and during ischemia, and at 5, 10, 15, 60, 120, and 240 minutes after the return of ocular circulation. In another two series of cats, blood flow was measured at comparable time periods without ischemia (controls). Arterial blood gas tension, systemic arterial pressure, hematocrit, and anesthetic level were controlled in each experiment. RESULTS Retinal blood flow was decreased to 6%, and choroidal blood flow to 0.6%, of baseline value during ischemia. Within 5 minutes of the return of ocular circulation, retinal blood flow was approximately 200% of baseline, and choroidal blood flow was 108% of baseline. Blood flow 1 hour after the return of ocular circulation was not significantly different from baseline. There was no late decrease in blood flow after the ischemic period. CONCLUSION As does cerebral ischemia, retinal ischemia results in a hyperemic response but no delayed hypoperfusion. The mechanism of this effect is unknown.