Oxygen Tension and Blood Flow in the Retina of Normal and Diabetic Rats

Abstract

In man and most mammals the retina is nourished by two highly specialised vascular systems, the choroidal and the retinal. Despite the high metabolic demands of the retina the extent of the retinal vasculature is constrained by the requirement of minimal disruption of the light path. In contrast, the choroidal circulation, behind the retina, is highly vascularised and has an unusually high flow rate. The avascular layers of retina between these two circulations are dependent on diffusion of metabolites over considerable distances. It is perhaps then not surprising that systemic diseases which affect the microvasculature, such as diabetes, often produce sight threatening complications in the eye. The role of hypoxia and ischaemia in such cases is widely accepted but there have been few direct measurements reported. The rat offers a very convenient model in which to study the early stages of diabetes, and the sequence of histological changes are well documented (Robison et al., 1990). We have developed microelectrode based techniques for the direct measurement of oxygen tension and blood flow in the eyes of normal and diabetic rats (Alder et al., 1990; Cringle et al., 1990; Yu et al., 1991). This paper is essentially a review of our preliminary findings in what we believe will become a valuable preparation for the study of retinal oxygen supply in the presence of systemic vascular disease.