Effects of hyperoxia on the oxygen distribution in the intact cat retina

Double-barreled oxygen microelectrodes were used to measure the distribution of oxygen within the dark adapted cat retina during systemic hyperoxia (100% O2 inspired). Oxygen tension (PO2) decreased monotonically from the choroid to the vitreous humor in most cases, showing that a greater portion of the retina was supplied by the choroid during hyperoxia than during normoxia. In the proximal half of the retina the PO2 increased during hyperoxia by an average of about 40 mm Hg, while the increase in the distal retina was larger. At the choroid the average increase in PO2 was about 150 mm Hg. Analysis of the oxygen profiles showed that photoreceptor oxygen consumption was unchanged during hyperoxia. Retinal PO2 increased rapidly at the beginning of hyperoxia, and often partially recovered from its peak value during hyperoxia, even in the distal retina, suggesting that the choroidal circulation may have some limited autoregulatory capacity. As in normoxia, retinal illumination led to an increase in PO2 in the distal retina, due to a decrease in oxygen consumption. The light-evoked increase in PO2 was larger during hyperoxia, but the underlying change in oxygen consumption was probably the same as in normoxia.