Intraretinal Oxygenation and Oxygen Consumption in the Rabbit during Systemic Hyperoxia

PURPOSE: To determine the ability of the retina and choroid in the avascular region of the rabbit retina to regulate intraretinal oxygen levels during periods of acute systemic hyperoxia. METHODS: Oxygen-sensitive microelectrodes were used to measure oxygen tension as a function of depth through the retina and choroid in anesthetized rabbits before and after stepwise incremental increases in inspired oxygen level. The extent of any oxygen increases throughout the retina and choroid was determined, and retinal oxygen consumption was determined by analyzing intraretinal oxygen distribution. RESULTS: Increases in systemic arterial oxygen in the rabbit resulted in significant increases in oxygen tension in the choroid and in all retinal layers. There was no apparent regulation of choroidal oxygen tension, as seen in the avascular retina of the guinea pig. Neither was there any increase in oxygen consumption within the retina, which has been shown to dampen the extent of raised oxygen levels in the inner retina in other mammals. Consequently, all retinal layers in the avascular area of the rabbit retina were exposed to high oxygen levels during systemic hyperoxia. The magnitude of the oxygen changes in all retinal layers was consistent with that in the preretinal vitreous. CONCLUSIONS: Unlike other mammals studied to date, the rabbit does not possess any regulatory mechanisms for controlling the intraretinal oxygen environment during acute increases in systemic arterial oxygen levels. This may well account for the reported vulnerability of the rabbit retina to toxic damage during extended periods of systemic hyperoxia.