purpose. To determine the intraretinal oxygen distribution and oxygen consumption in the rat before eye opening and maturation of the retina.

methods. Oxygen-sensitive microelectrodes were used to measure the oxygen tension as a function of depth through the retina in anesthetized Sprague–Dawley rats at postnatal day (P) 15. Measurements were made under air-breathing conditions and at increasing levels of systemic oxygenation (20%, 40%, 60%, 80%, and 100% oxygen) under light-adapted conditions. Oxygen consumption in the outer retina and in the predominantly avascular region of the inner retina was assessed by fitting the oxygen profiles to a mathematical model of oxygen consumption. The retinas were processed for histology and compared with retinas from mature animals.

results. Under normal conditions, the intraretinal oxygen distribution at P15 was significantly different in some respects from that in mature animals. Oxygen consumption analysis indicated an average outer retinal oxygen consumption rate of 103±15 nL/min per cm 2 and an inner retinal oxygen consumption rate of 42.4±11.7 nL/min per cm 2. Inner retinal oxygen consumption was significantly (P< 0.001) lower than that previously measured in mature rats, but outer retinal oxygen consumption was similar. Systemic hyperoxia increased the oxygen level throughout the retina, but choroidal P o 2 in particular remained significantly lower than in adult rats (P< 0.001). At P15 there were marked differences in the relative thickness of some retinal layers when compared with adult rats. In particular the inner and outer nuclear layers were much thicker at P15, the outer segments of the photoreceptors and the inner and outer plexiform layers were not fully developed.

conclusions. At P15, before eye opening, the oxygen consumption of the inner retina is lower than in mature retinas, presumably reflecting the immaturity of the retina in such young animals so soon after their first exposure to light stimuli.