Quantitative Retinal and Choroidal Blood Flow During Light, Dark Adaptation and Flicker Light Stimulation in Rats Using Fluorescent Microspheres

Purpose: The present study aimed to quantify retinal and choroidal blood flow (BF) during light, dark adaptation and flicker light stimulation using the microsphere technique. Materials and Methods: Adult male Sprague-Dawley rats were anesthetized with isoflurane. Eyes were dark (Group I, n = 8), light (Group II, n = 8) adapted or stimulated with 10Hz flicker light (Group III, n = 10). Retinal and choroidal BF were measured by a previously established method, using a mixture of 8 mm yellow-green and 10 mm red fluorescent microspheres. The microspheres were counted ex vivo in the dissected retina and choroid and in the reference arterial blood under a fluorescent microscope. Results: The choroidal BF was 64.8 +/- 29 mu l/min (mean +/- SD) during dark adaptation, not significantly different from that during light adaptation (66.0 +/- 17.8 mu l/min). The retinal BF was 13.5 +/- 3.2 mu l/min during 10 Hz flickering light stimulation, significantly higher than that during dark adaptation in the control fellow eyes (9.9 +/- 2.9 mu l/min). The choroidal BF values were not statistically different between flicker stimulation and dark adaptation. Retinal BF was 11.6 +/- 2.9 mu l/min during light adaptation. Dark adaptation did not increase retinal BF (Group I, 8.2 +/- 2.4 mu l/min; Group II, 9.9 +/- 2.9 mu l/min). Conclusions: These findings argue against a dark-induced or flicker-induced functional hyperemia in the choroid as a result of the demands of the outer retina. Retinal BF was not higher during dark adaptation. Our data support the conclusion that the inner retina has a higher energy demand in flicker conditions relative to dark.