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S. Basit, S. H. Hardarson, G. H. Halldorsson, R. A. Karlsson, J. M. Beach, T. Eysteinsson, J. A. Benediktsson, A. Harris, E. Stefansson; Oxygen Saturation in Human Retinal Arterioles and Venules Is Lower in Light Than in Dark. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4172.
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Earlier studies on animals have indicated that oxygen tension in the inner retina is lower in light than in dark (Linsemeier, Braun 1992), whereas the oxygen consumption in the outer retina is lower in light (Stefánsson et al 1983, 1988). The purpose of the study was to measure the hemoglobin oxygen saturation (SatO2) in retinal vessels after periods of dark and light in human subjects.
Our automatic non-invasive retinal oximeter yields fundus images with isosbestic and non-isosbestic wavelengths of light simultaneously and calculates optical density ratio, which is approximately linearly related to SatO2. We performed oximetry in 9 healthy male volunteers. First degree arterioles and venules were measured in one eye of each subject. The subjects were first placed in the dark for 30 minutes, then in room light for 5 minutes, and then in dark again for 5 minutes. Oximetry was performed at the end of each period. Repeated-measures ANOVA with Bonferroni post-test was used for statistical analysis.
In arterioles the SatO2 was 97±5% (mean±SD, n=9) after 30 minutes in dark, 93±3% after 5 minutes in light and 97±4% after 5 minutes in dark. In venules, the SatO2 was 61±6%, 53±8% and 59±7%, respectively. The SatO2 in arterioles was significantly lower in light compared to both after 30 minutes (p<0.05) and 5 minutes (p<0.01) in the dark. The SatO2 in venules was also significantly lower in light than in dark (p<0.01 for 30 minutes and p<0.05 for 5 minutes in dark).
These results suggest that the hemoglobin oxygen saturation is lower in both retinal arterioles and venules when the retina is in light compared to when it is in dark. To our knowledge, this is the first direct demonstration of the effect of light and dark on the oxygen metabolism of the human retina. The results are in agreement with earlier animal studies.
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