Retinal Oximetry Imaging in Alzheimer's Disease

Background: Structural and physiological abnormalities have been reported in the retina in Alzheimer's disease (AD). Retinal oximetry detects changes in retinal oxygen metabolism in many eye diseases, where structural changes are seen. Objective: To compare oxygen saturation in retinal blood vessels in patients with AD and a healthy cohort. Methods: Oxygen saturation of hemoglobin was measured in retinal blood vessels, using imaging with spectrophotometric noninvasive retinal oximeter. 18 individuals with mild to moderate dementia of the Alzheimer-type (stage 3-5 according to the Global Deterioration Scale) and 18 healthy subjects underwent retinal oximetry in a case control study. Results: Retinal oxygen saturation in arterioles and venules in patients with moderate AD was significantly elevated compared to healthy individuals. Retinal arterioles have 94.2 +/- 5.4% oxygen saturation in moderate AD compared with 90.5 +/- 3.1% in healthy subjects (mean +/- SD, n = 10, p = 0.028). Retinal venules were 51.9 +/- 6.0% saturated in moderate AD compared with 49.7 +/- 7.0% in healthy subjects (mean +/- SD, n = 10, p = 0.02). Conclusion: This is the first study of retinal oxygen metabolism in any central nervous system disease. It discovers abnormalities in retinal oxygen metabolism in AD. The findings are similar to those seen in age-related macular degeneration and diabetic retinopathy. Noninvasive retinal oximetry may offer new insights into pathophysiology of AD. Further studies are needed to confirm and expand these findings.