Intraretinal and preretinal PO2 response to acutely raised intraocular pressure in cats

The effect of acutely raised intraocular pressure (IOP) on retinal oxygenation has been determined using oxygen-sensitive microelectrodes preretinally and intraretinally. Anesthetized cats were ventilated alternately with one of two oxygen concentrations, 21 or 100%, while the IOP was manipulated via a hydrostatic pressure head connected to the anterior chamber. Preretinal and inner retinal oxygen tension remained stable over a broad range of IOP for air breathing. In contrast, the outer retina was severely affected, with the PO2 reducing as IOP was raised, resulting in some areas becoming anoxic. Outer retinal oxygen consumption was reduced for perfusion pressures less than 50 mmHg. It is postulated that under air-breathing conditions the preretinal and inner retinal oxygen tension was stabilized by the autoregulatory capacity of the retinal circulation. The inability of the choroidal circulation to autoregulate was reflected in the reduction of outer retinal oxygen tension with increasing IOP. With 100% oxygen breathing, increases in IOP caused a significant reduction in PO2 throughout the entire retina and preretinal vitreous. It is proposed that the effect of the autoregulatory capacity of the retinal circulation on retinal oxygenation is reduced in hyperoxia.