BLOOD-FLOW AFTER RETINAL ISCHEMIA IN CATS

Purpose. To determine the changes in blood flow in the cat retina afte r 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 micr ospheres. Ischemia was induced by elevation of intraocular pressure ab ove systolic arterial pressure. Measurements were carried out before ( baseline) and during ischemia, and at 5, 10, 15, 60, 120, and 240 minu tes after the return of ocular circulation. In another two series of c ats, blood flow was measured at comparable time periods without ischem ia (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 t he 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 significan tly different from baseline. There was no late decrease in blood flow after the ischemic period. Conclusion. As does cerebral ischemia, reti nal ischemia results in a hyperemic response but no delayed hypoperfus ion. The mechanism of this effect is unknown.