The effect of photocoagulation on the oxygenation and ultrastructure of avascular retina

Panretinal photocoagulation has been shown to raise preretinal oxygen tension in cats and monkeys breathing 100% oxygen. However, in normoxia, there is no significant difference between normal and photocoagulated areas. This is thought to be due to autoregulatory vasoconstriction of the retinal circulation. In avascular rabbit retina, photocoagulation effects on retinal oxygenation can be studied without the influence of retinal vascular autoregulation. We measured normoxic preretinal oxygen tension of normal and photocoagulated rabbit retina at 1, 7, 14 and 28 days after photocoagulation using polarographic oxygen electrodes. For all time points, preretinal oxygen tension of photocoagulated retina (42 +/- 14 torr; mean +/- S.D.) was higher than untreated retina (14 +/- 10 torr; mean +/- S.D., P less than 0.001). Light and electron microscopy of lasered retina showed that the improved oxygenation corresponded to loss of mitochondria-rich inner segments of the photoreceptors.