The response of rat vitreal oxygen tension to stepwise increases in inspired percentage oxygen

The effect of graded systemic hyperoxia on vitreal PO2 distribution has been determined for the rat eye. Oxygen tension profiles were measured, using oxygen-sensitive microelectrodes, as a function of distance from the internal limiting membrane as the inspired oxygen percentage was increased in 10% steps from 20-100%. Depending on the original touching location of the microelectrode on the retina, there could be substantial PO2 gradients within 500 microns of the retina; at greater distances vitreal PO2 was constant and a function of the inspired oxygen percentage. Whatever the location of the microelectrode in the vitreous, PO2 rose with increasing hyperoxia. The relationship between vitreal PO2 and inspired oxygen was nonlinear with a central relatively flat region between 50-80% inspired oxygen. The ratio between vitreal PO2 during 100% O2 breathing and air breathing was 3.42 +/- 1.08 (standard deviation, n = 7). Possible explanations for the plateau region are the maintenance of a relatively constant PO2 by vascular autoregulation and/or the buffering of capillary PO2 by hemoglobin. The rat eye, therefore, responds to hyperoxia similarly to that of the cat and monkey but differs from that of the miniature pig where there is no rise in preretinal PO2 during hyperoxia.