The Oxygen Supply to the Retina, I. Effects of Changes in Intraocular and Arterial Blood Pressures, and in Arterial PO2 and Pco2 on the Oxygen Tension in the Vitreous Body of the Cat

The Po 2 in the vitreous body close to the retina, P vrO2 , was determined continuously with an O 2 electrode. In cats with a mean arterial blood pressure of 176±7 cm H 2 O, a P aO2 of 98±2 mm Hg, a P aC02 of 27.0±1–2 mm Hg and a pH of 7.43±0.16 units the mean P V r02 was 18.9±1.5 mm Hg. Stepwise increments in the eye pressure had no effect on P V r O2 at perfusion pressures above 50–100 cm H 2 O. At lower perfusion pressures P vrO2 decreased. Changes in perfusion pressure caused by hemorrhage and retransfusion gave similar results. At low P aco2 levels P vrO2 decreased; at high P aCo2 levels values of 40–60 mm Hg were observed. Reductions in P ao2 decreased P vro2 , increments gave either no change or a rise in P vr02 ‐ Hypercapnia combined with high P a o 2 in several cases resulted in P Vr02 values between 100 and 150 mm Hg. The results indicate that the blood flow through the retina is very efficiently autoregulated, that oxygen tends to induce vasoconstriction in the retinal blood vessels, that hypocapnia gives vasoconstriction and hypercapnia marked vasodilatation.