The long term objective is to deepen our understanding of the pathogenesis of diabetic retinopathy and of the basis for treating this disease by photocoagulation. A widely believed, but unsubstantiated, working hypothesis is the retinal ischemia or hypoxia is responsible for retinal neovascularization. Direct noninvasive measurement of tissue oxygenation in the human retina could provide the data necessary to test this hypothesis. The technique of redox fluorimetry has been used to assess oxygenation of non-ocular tissues. We have adapted this technique for use in the eye and have built an instrument for noninvasively measuring the fluorescence of the flavin adenine dinucleotide (FAD) moiety of flavoprotein. FAD is an electron carrier in the mitochondrial electron transport chain whose fluorescence intensity decreases during hypoxia. The purpose of the proposed work is to do the critical experiments that will tell us how to best use measurements of retinal flavoprotein fluorescence to determine the oxygenation of the retina. We would like to produce a map of the retina that shows its oxygenation, and which gives the location and severity of focal patches of retinal hypoxia. Experiments with monkeys and with patients with known defects in the retinal circulation are designed to validate the use of redox fluorimetry in the retina. Comparisons between normals and patients with proliferative retinopathy will be used to test the hypoxia hypothesis above. Comparison of maps of retinal flavoprotein fluorescence with fluorescein angiograms in patients at different stages of diabetic retinopathy may establish the relationship between anatomic and functional abnormalities in the course of the disease. The clinical significance of this work is that it may facilitate more selective application of photocoagulation in the treatment of diabetic retinopathy.