Intraretinal oxygen consumption in the rat in vivo.

PURPOSE: To make the first quantitative assessment of the rate of oxygen consumption in high oxygen-consuming layers of both the outer and inner retina of the rat in vivo.
METHODS: Oxygen-sensitive microelectrodes were used to measure the oxygen tension as a function of depth through the retina in anesthetized rats. Individual PO2 profiles were fitted to a multilayer mathematical model of PO2 distribution that is able to determine the oxygen uptake in those retinal layers in which the oxygen supply is through diffusion from vascular layers of the retina. This includes the entire outer retina and the region of the inner retina containing the inner plexiform layer. Measurements were performed in the light (13 mW/cm2 at the cornea) and in the dark and the amplitude and time constant for light-induced changes in outer retinal oxygenation determined.
RESULTS: Under light-adapted conditions, the oxygen consumption of the outer retina was 148 +/- 11 nL O2/min/cm2 (n = 20) [corrected] and that of the included portion of the inner retina was 184 +/- 17 nL O2/min/cm2 [corrected]. In the dark, outer retinal oxygen consumption increased by 47.8% (P < 0.001), and the time constant for the resultant PO2 decrease in the outer retina was 14.9 +/- 1.8 seconds (n = 16). There was no significant change in inner retinal oxygen consumption between light and dark conditions (P = 0.89).
CONCLUSIONS: Under light-adapted conditions the oxygen uptake by the selected region of the inner retina (primarily the inner plexiform layer) is greater than that of the outer retina (P < 0.01). Dark adaptation rapidly and significantly increases outer retinal oxygen consumption, but the inner retina remains unaffected.