Oxygen distribution in the retina

Abstract

AbstractPurpose To evaluate the distibution of the preretinal and transretinal partial pressure of oxygen(PO2) in normal and ischemic retinas.Methods Evaluation of either the preretinal or intraretinal oxygen partial pressure (PO2) distribution, using oxygen sensitive microelectrodes, in normal or ischemic retinal conditions.Results The distribution of PO2 close to the vitreoretinal interface is heterogeneous, being higher near the arteriolar wall. Preretinal and transretinal PO2 profiles indicate that O2 diffusion from the arterioles affects the PO2 in the juxta‐arteriolar preretinal region. Both the preretinal and inner retinal PO2 recorded far from the vessels remain constant in all retinal areas. The oxygen tension (PO2) in the inner half of the retina remains largely unaffected by moderate changes in perfusion pressure, systemic PaO2 changes occuring during either hyperoxia or hypoxia. However, an increase in PaCO2 (hypercapnia), as well as an intravenous injection of acetazolamide (carbonic anhydrase inhibitor) both lead to an increase in preretinal PO2 due to dilation of the retinal vessels. In eyes with experimental branch retinal vein occlusion, PO2 values within the inner retinal layers are indicative of hypoxic conditions, whereas adjacent areas appear to remain normal. In diabetic patients undergoing vitrectomy a lowered vitreal PO2 in the affected retinal areas has also reported.Occlusion of the retinal circulation renders most of the inner retina anoxic.Conclusion Thanks to the autoregulatory ability of the retinal circulation, the oxygen tension (PO2) in the inner half of the retina, remains largely unaffected during physiological stimuli. In both normal and inner retinal ischemic conditions,the oxygen supply from the choroid is sufficient to support only the photoreceptor inner segments.