Oxygen consumption in the inner and outer retina of the cat

Purpose. Oxygen consumption rate (QO₂) was determined in the outer and inner halves of the cat retina in dark and light adaptation. Methods. Double- barreled oxygen microelectrodes were used to measure oxygen tension (PO₂) across the retina of anesthetized cats while the single retinal artery supplying that area was occluded. During the measurements of these PO₂ profiles the cats were ventilated with 100% O₂. Retinal PO₂ profiles were fitted to a diffusion model, and inner and outer retinal QO₂s were determined from the fitted parameters. Results. A four-layer model, in which two layers consumed oxygen, fitted the data well. One consuming layer corresponded to the photoreceptor inner segments, as in previous studies, and a single region of uniform consumption was used to describe the profile in the inner half of the retina. Under dark-adapted conditions, outer and inner retinal QO₂ were 3.9 ± 2.8 and 3.5 ± 1.7 ml O₂/(100 g · min) (mean ± SD; 9 cats), respectively. With steady illumination, outer retinal (photoreceptor) QO₂ decreased to 1.4 ± 0.9 ml O₂/(100 g · min), but inner retinal QO₂ remained unchanged at 3.7 ± 1.5 ml O₂/(100 g · min) (5 cats). Conclusions. The total QO₂ of the inner retina was found to be the same as that of the dark-adapted outer retina. Oxygen use was distributed uniformly throughout the inner retina but was confined to the photoreceptor inner segments, which occupied approximately 20% of the thickness of the outer retina. Steady illumination had no effect on inner retinal QO₂.