Comparison of retinal transit times and retinal blood flow: A study in monkeys

PURPOSE. TO determine the correlation between transit times of retinal bloo d now calculated from fluorescein angiograms and retinal blood flow determi ned by the microsphere method. METHODS. Two fluorescein angiograms were obtained in each eye of six monkey s, followed by determination of retinal blood flow with labeled microsphere s. Angiograms in 10 eyes were analyzed for mean transit time (MTT) and arte riovenous passage time (AVP). MTT was determined in two ways: from dye curv es reconstructed by extrapolation of semilogarithmic plots of the recorded curves (MTT) and by a new technique based on an impulse-response analysis ( MTTir). RESULTS. Mean values (+/-SD) for retinal blood flow in 10 eyes were 23.2 +/ - 6.9 mg/min. Corresponding values for MTTslope, and AVP were 2.22 +/- 0.38 , 4.89 +/- 5.89, and 1.08 +/- MTT 0.14 seconds. There was a weak, but not s tatistically significant, correlation between retinal blood flow and MTTir (r -0.60, P = 0.06) but no useful correlation between retinal blood now and either MTTslope or AVP. slope CONCLUSIONS. The relationship between retinal blood flow and transit times determined from fluorescein angiograms is weak. Of the three transit parame ters tested, MTTir, determined with the recently developed impulse-response technique, had the best correlation with retinal blood flow. Further studi es are needed to determine the ability of these transit parameters to detec t a change in retinal blood now and the possibility that transit times may provide useful clinical information unrelated to absolute values of retinal blood flow.