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Oxygen distribution and consumption in the macaque retina

Departments of ¹Biomedical Engineering and ²Neurobiology and Physiology, Northwestern University, Evanston, Illinois

Submitted 20 February 2007 ; accepted in final form 6 June 2007

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 Q_av) was 4.6 ± 2.3 ml O₂·100 g^–1·min^–1 under dark-adapted conditions. Illumination sufficient to saturate the rods reduced Q_av 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.

nonhuman primate; monkey; retinal metabolism; photoreceptor; fovea