Vitreal and retinal oxygenation.

This paper reports the results of experiments carried out to understand the oxygenation of the normal retina in response to alterations in physiological conditions such as inspired oxygen concentration, elevated IOP, luminance changes and occlusion of the retinal circulation. Measurements of vitreal and intraretinal PO2 in vivo in the cat using oxygen-sensitive microelectrodes demonstrated that large PO2 gradients were set up preretinally and that arterial, venous and tissue PO2 increased when inspired PO2 was raised to 100% O2. Results showed that with an occluded retinal circulation, it was possible to oxygenate fully the whole retina with oxygen supplied from a hyperoxic choroidal circulation. With alterations in background luminance from photopic to scotopic, preretinal PO2 was unaffected for air breathing, whereas for 100% O2, breathing vitreal PO2 fell quickly and reversibly on a switch from photopic to scotopic conditions, reflecting an increase in retinal oxygen consumption in a dark environment. During acute rises of IOP, the PO2 at the choriocapillaris fell and an anoxic region developed in the middle retinal layers. The inner retina was relatively resistant to rises in IOP. The implications of these data for autoregulation of the retinal circulation are discussed.