Oxygen distribution and consumption in the cat retina at increased intraocular pressure

Oxygen microelectrodes were used to study the distribution of oxygen in the retina of dark adapted anesthetized cats during short term elevation of intraocular pressure (IOP) that reduced the perfusion pressure (PP = mean femoral arterial pressure - IOP) to as low as 40 mm Hg. The oxygen tension (PO₂) in the inner half of the retina was affected very little over this range. Choroidal PO₂, however, decreased substantially, about 0.5 mm Hg per mm Hg perfusion pressure, in the area centralis and superior retina (15-20° superior to the area centralis). This decreased the oxygen available to that part of the outer retina supplied by the choroidal circulation. Oxygen consumption was estimated by fitting profiles of PO₂ as a function of distance to a diffusion model. This analysis showed that photoreceptor oxygen consumption decreased significantly at perfusion pressures less than 70 mm Hg in the area centralis. Changes in consumption were also observed in the superior retina, but were not significant. Oxygenation of a region just nasal to the optic disc was also studied, but neither the choroidal PO₂ nor oxygen consumption in this area was affected over the range of PP studied. These results provide direct evidence that moderately increased IOP leads to a decrease in choroidal PO₂ and sufficient hypoxia in the distal retina to cause a reduction in photoreceptor oxygen consumption. This presumably slows the photoreceptor Na⁺/K⁺ pump and leads to the ERG changes reported previously (Yancey and Linsenmeier, Invest Ophthalmol Vis Sci 29:700, 1988).