Chorioretinal vascular oxygen tension changes in response to light flicker

PURPOSE. To investigate oxygen tension (Po-2) changes in the retinal and choroidal vasculatures in response to visual stimulation by light flicker. METHODS. A previously developed optical section phosphorescence imaging system was used to measure Po-2 separately in the retinal veins, arteries, and capillaries and in the choroid before and during light flicker. Imaging was performed in rats during light flicker at frequencies between 0 and 14 Hz. Light flicker-induced changes in the chorioretinal vasculature Po-2 and arteriovenous Po-2 differences were determined. Retinal arterial and venous Po-2 were measured along blood vessels as a function of the distance from the optic nerve head. RESULTS. Retinal arterial Po-2 and arteriovenous Po-2 differences increased with increasing light flicker at frequencies up to 10 Hz, after which no further increase was observed. Significant increases in retinal arterial Po-2 (P = 0.009; n = 10) and in retinal capillary Po-2 (P = 0.04, n = 10) were measured in response to light flicker at 10 Hz. Retinal arteriovenous Po-2 differences during light flicker were significantly greater than differences before light flicker (P = 0.01; n = 10). Retinal arterial Po-2 decreased significantly with increased distance from the optic nerve head (P <= 0.004), whereas retinal venous Po-2 remained relatively unchanged (P >= 0.4). CONCLUSIONS. Measurement of changes in the chorioretinal vasculature Po-2 can potentially advance the understanding of oxygen dynamics in challenged physiological states and in animal models of human retinal diseases.