PO2 profiles and oxygen consumption in cat retina with an occluded retinal circulation

If the retinal circulation is occluded, the retina is forced to rely on the choroidal circulation for its oxygen supply. We have measured intraretinal PO2 profiles before, during, and after such an occlusion in cat. Oxygen-sensitive microelectrodes were used to measure intraretinal PO2, and the retinal circulation was occluded by means of a glass probe placed on the retinal vessels at the optic disk. Both air and 100% O2 breathing conditions were investigated. With the retinal circulation occluded, intra-retinal PO2 fell to zero within 60% of the distance through the retina, measured from the choriocapillaris to the internal limiting membrane. With the circulation occluded, but with breathing of 100% O2, PO2 rose throughout the retina so that values within the inner retina were as high or higher than for air breathing with the retinal circulation present. This meant that the whole retina could be supplied with adequate oxygen by breathing with 100% O2 in cat. From these PO2 profiles, oxygen flux and consumption were calculated as a function of distance through the retina. These calculations showed that the outer 20% of the retina had a consumption of 5.45 +/- 2.46 (SD) ml.min-1.100 ml-1 compared with a mean value for the remaining retina of 1.47 +/- 2.66 ml.min-1.100 ml-1. This difference was statistically significant (P less than 0.001) which indicates that there are at least two regions in the retina with different oxygen consumption.