Effects of photocoagulation on intraretinal PO₂ in cat

PURPOSE. To test the hypothesis that intraretinal PO₂ increases after photocoagulation. METHODS. Anesthetized cats underwent retinal argon laser photocoagulation. At least 4 weeks after treatment, PO₂-sensitive microelectrodes were used to record intraretinal PO₂ profiles from healed photocoagulation lesions in anesthetized cats breathing air. Histopathologic examination of the retinas was used to confirm that the photoreceptors were destroyed and that the inner retinal layers were preserved, though somewhat disorganized, as in human panretinal photocoagulation (PRP). RESULTS. The retina and tapetum were thinner in the lesioned retina than in the nonphotocoagulated retina. Average PO₂ across the inner 50% of the retina was higher (22 ± 10 mm Hg) in photocoagulated retina than in untreated retina (14 ± 7 mm Hg; P < 0.01; n = 13 cats). The minimum PO₂ was also significantly higher, whereas choroidal PO₂ was significantly lower in the photocoagulated retina than in untreated retina. No significant difference was found in the preretinal vitreous. After lesions, inner retinal PO₂ could also be maintained above zero, even in the absence of retinal circulation. CONCLUSIONS. Previous measurements showed increased PO₂ in the preretinal vitreous of rabbits and pigs (but not cats) after photocoagulation of the outer retina. These intraretinal measurements in cats provide further evidence for a chronic increase in inner retinal PO₂ in lesioned areas during air breathing.