Retinal oxygen tension and the electroretinogram during arterial occlusion in the cat

Purpose. Retinal oxygen tension (PO₂), photoreceptor oxygen consumption (QO₂), the local electroretinogram (LERG), and the vitreally recorded electroretinogram (ERG) were evaluated during retinal artery occlusion in the cat. The feasibility of supplying the retina with oxygen during occlusion by ventilation with 100% O₂ was evaluated. Methods. Double-barreled oxygen microelectrodes were used to measure intraretinal PO₂ and LERGs in anesthetized cats before, during, and alter occlusion of a single retinal artery. Outer retinal (photoreceptor) QO₂ was determined from retinal PO₂ profiles. Results. During air breathing, occlusion obliterated the LERG b- wave and reduced the vitreal ERG by the amount expected from the area supplied by the occluded vessel. The PO₂ in the entire inner retina was zero, and photoreceptor QO₂ was decreased by approximately 25%. Inspiration of 100% O₂ restored the b-wave amplitude to approximately 50% of normal and increased the amount of O₂ reaching the inner retina. Hyperoxia could not guarantee nonzero PO₂ across the entire retina in either darkness or light, but it elevated the average PO₂ in the innermost 25% of the retina to more than 20 mm Hg. The b-wave amplitude must have been affected by some factor in addition to local hypoxia, because the amplitude was not correlated with inner retinal PO₂ during occlusion, and a normal PO₂ did not result in a normal LERG. Effects of 2 to 2.5 hours of occlusion were reversible if 100% O₂ inspiration was maintained during most of the occlusion. Conclusions. Ventilation with 100% O₂ during occlusion increased the PO₂ across most of the retina and partially restored the LERG b-wave, but the tissue near the vitreous was still sometimes anoxic. The illumination status seemed to make little difference. Inspiration of elevated O₂ might be beneficial in treating retinal vascular occlusive disease, although it alone cannot completely maintain retinal function.