Retinal oxygen saturation in humans in light and dark

Abstract

Purpose: To investigate the effect of light and dark on the retinal vessel oxygen saturation (SatO2) in healthy humans. Methods: The oximeter consists of a fundus camera, a beam splitter, a digital camera and software, which calculates the SatO2 of the retinal vessels. In the first experiment, 18 healthy individuals were first placed in the dark for 30 minutes, then alternatingly in light (80cd/m2) and dark. Each light or dark period lasted for 5 minutes. In the second experiment, 23 volunteers were measured. The volunteers were placed in the dark for 30 minutes and then in light successively at 1, 10 and 100 cd/m2, each period lasting 5 minutes. Finally, the volunteers were adapted to dark for 5 minutes. Oximetry was performed at the end of each period in both experiments. Three individuals were excluded from the first experiment and 4 from the second because of poor image quality. Paired t‐tests were used for analysis. Results: In the first experiment, arterial SatO2 was 3‐4% higher in the dark than after subsequent adaptation to 80cd/m2 light (p<0.05) and similar results were seen in venules; 3‐7% higher SatO2 values in the dark (p<0.05). In the second experiment, arterial SatO2 was 3% higher in the dark than after adapatation to 100cd/m2 (p=0.01) and the corresponding difference in venules was 5% (higher in the dark, p=0.06). SatO2 was not significantly different between dark and 1 or 10cd/m2. Conclusions: The results indicate that SatO2 is higher in dark than in light in both arterioles and venules. The higher SatO2 in dark may reflect the increased oxygen consumption in the dark, which has to be compensated for by increasing the oxygen gradient between the retinal vasculature and tissue.