Intraretinal oxygen levels before and after photoreceptor loss in the RCS rat.

PURPOSE To measure the intraretinal oxygen environment at different stages in the Royal College of Surgeons (RCS) rat model of retinal degeneration to determine whether changes in oxygen level are an important aspect of the disease. METHODS Oxygen-sensitive microelectrodes were used to measure oxygen tension as a function of depth through the retina of anesthetized, mechanically ventilated RCS rats at ages ranging from postnatal day (P)20 to P104. The oxygen profiles were correlated with histologic observations of the cellular changes within the dystrophic retinas and compared with those in RCS-rdy(+) control animals and published values in normal mature rats. RESULTS Although the youngest rats studied exhibited some differences in intraretinal oxygen distribution compared with mature animals, the distribution in dystrophic RCS rats at P20 was not significantly different from that in age-matched control subjects. However, the intraretinal oxygen distribution in dystrophic RCS rats was clearly affected after approximately P30, reflecting a loss of photoreceptor oxygen consumption consistent with histologic observations. In contrast, oxygen uptake by the inner retina was still evident long after the loss of photoreceptors was essentially complete. CONCLUSIONS There was no significant tissue hypoxia during photoreceptor degeneration in the dystrophic RCS rat. The changes in intraretinal oxygen distribution are consistent with the loss of outer retinal oxygen uptake but the preservation of inner retinal oxygen metabolism.