A New Non-invasive Metabolic Assessment Technique in Glaucoma Research

Abstract

Abstract: : Purpose: Reduced blood flow has been implied in pathogenesis of glaucoma, however its impact on retinal metabolic status remains unknown. The purpose of this study is to assess retinal arterial and venous blood oxygen saturation (O2sat) using a digital retinal oximeter. Method: All procedures were approved by an IRB, and informed consent obtained. Thirty-two oximetry images (12 male, 20 female) were obtained in 14 normal healthy adults (mean 37.1 years, SD=9.1) using a newly developed digital retinal oximeter. Optical density ratios (ODR) were calculated from oxygen sensitive and insensitive (Hb=HbO2) wavelengths. Using an experimentally derived calibration constant, arterial and venous blood oxygen saturation was calculated from the ODRs. Oxygen extraction was calculated as arterial O2sat - venous O2sat. Results: In normal healthy humans, retinal arterial saturation was found to be 98.0% (SD 1.0%) overall, 97.5% (SD 1.2%) in males, and 98.5% (SD 0.5%) in females. Venous oxygen saturation was 82.9% (SD 14.8%) overall, 79.0% (SD 19.9%) in males, and 86.1% (SD 11.9%) in females. Oxygen extraction was 15.4% (SD 14.9%) overall, with 18.5% (SD 18.4%) in males, and 12.4% (SD 11.7%) in females. Conclusion: The ability to non-invasively measure retinal vessel oxygen saturation and retinal oxygen extraction in humans, when coupled with a comprehensive blood flow analysis, provides an important objective assessment tool for the studying metabolic events in human glaucoma.

Keywords: blood supply • imaging/image analysis: clinical • ischemia