Intraretinal oxygren distribution and consumption during retinal artery occlusion and graded hyperoxic ventilation in the rat

PURPOSE. To determine intraretinal oxygen distribution and consumption in a rat model of retinal artery occlusion during air breathing and stepwise systemic hypetioxia. METHODS.. Laser occlusion of the pair of retinal arteries feeding the area of retina under investigation was performed. Oxygen-sensitive microelectrodes were then used to measure oxygen tension as a function of depth through the retina. Breathing mixtures were manipulated to produce stepwise increments in systemic oxygen levels, and the measurement of intraretinal oxygen distribution was repeated. Oxygen distribution in the retina was analyzed by an established eight-layer mathematical model of retinal oxygen consumption. RESULTS. Intraretinal oxygen distribution in the occluded area confirmed that the choroid was the only source of retinal oxygenation. Under air-breathing conditions, the oxygen supply from the choroid was sufficient to support the photoreceptor inner segments. Any remaining oxygen was consumed by the outer plexiform layer. Increases in inspired oxygen level reduced the extent of inner retinal anoxia. However, some degree of anoxia in the innermost retina was usually present. CONCLUSIONS. Occlusion of the retinal circulation renders most of the inner retina anoxic. Ventilation with 100% oxygen does not generally avoid some degree of intraretinal anoxia. With 100% oxygen ventilation, the oxygen consumption of the inner retina was more than four times that of the outer retina. A marked degree of heterogeneity in oxygen uptake of different retinal layers was evident. The dominant oxygen consumers were the inner segments of the photoreceptors, the outer plexiform layer, and the inner plexiform layer.