Oxygen distribution and consumption in the macaque retina

Abstract

The oxygen distribution in the retina of six anesthetized macaques was investigated as a model for retinal oxygenation in the human retina in and adjacent to the fovea. Po2 was measured as a function of retinal depth under normal physiological conditions in light and dark adaptation with O2 microelectrodes. Oxygen consumption (Qo2) of the photoreceptors was extracted by fitting a steady-state diffusion model to Po2 measurements. In the perifovea, the Po2 was 48 ± 13 mmHg (mean and SD) at the choroid and fell to a minimum of 3.8 ± 1.9 mmHg around the photoreceptor inner segments in dark adaptation, rising again toward the inner retina. The Po2 in the inner half of the retina in darkness was 17.9 ± 7.8 mmHg. When averaged over the outer retina, photoreceptor Qo2 (called Qav) was 4.6 ± 2.3 ml O2·100 g−1·min−1 under dark-adapted conditions. Illumination sufficient to saturate the rods reduced Qav to 72 ± 11% of the dark-adapted value. Both perifoveal and foveal photoreceptors received most of their O2 from the choroidal circulation. While foveal photoreceptors have more mitochondria, the Qo2 of photoreceptors in the fovea was 68% of that in the perifovea. Oxygenation in macaque retina was similar to that previously found in cats and other mammals, reinforcing the relevance of nonprimate animal models for the study of retinal oxygenation, but there was a smaller reduction in Qo2 with light than observed in cats, which may have implications for understanding the influence of light under some clinical conditions.