Retinal Arterial Occlusion in the Cat: ERG Studies

Abstract

Abstract: : Purpose: This work assessed the hypotheses that (i) hyperoxia is preferable to air breathing during retinal arterial occlusion, and (ii) enhanced oxygen breathing would be beneficial in promoting recovery from an episode of arterial occlusion. Methods: Branch retinal artery occlusion was produced by pressing onto an artery emerging from the superior part of the optic disc in the retina of anesthetized cats with a glass probe. During the time of retinal occlusion, the cat was breathing either (i) 2 hours of air, or (ii) 1 hour of air and 1 hour of 70% oxygen, or (iii) 1 hour of air and 1 hour of 100% oxygen, or (iv) 2 hours of 100% oxygen. Single barreled voltage microelectrodes were used to record intraretinal ERGs before, during, and after the occlusion episodes. The vitreal ERG was also monitored. The vitreal and the local ERGs were analyzed by calculating b-wave and c-wave amplitudes. Since LERGs varied with retinal depth, as a convention, the b-wave values considered here reflect the amplitude at the depth of the maximum c-wave. Results: Our findings showed that (i) hyperoxia as opposed to air breathing during occlusion preserved intraretinal b-wave magnitude of ca. 85% of normal, (ii) longer episodes of increased oxygenation maintained b-wave magnitude at higher levels during occlusion, (iii) longer episodes of hyperoxia increased the probability of b-wave recovery after occlusion, (iv) higher oxygen content of the breathing gas increased b-wave magnitude during recovery, and (v) hyperoxia during occlusion decreased the time it took for the b-wave to recover following the end of occlusion. Conclusions: The results obtained in this study suggest that hyperoxia is preferable to air breathing during retinal arterial occlusion for not only maintaining b-wave during occlusion but also providing a shorter recovery time. Increasing oxygen content of the breathing gas improved LERG b-wave magnitude recovery.

Keywords: retina • blood supply • electroretinography: non-clinical