The association between retinal vascular network geometry and cognitive ability in an elderly population

PURPOSE. To test the hypothesis that parameters of retinal vascular network geometry are significantly associated with cognition. METHODS. Three hundred twenty-one community-dwelling, surviving participants in the Scottish Mental Survey of 1932 from the Lothian region of Scotland (Lothian Birth Cohort 1921; all born in 1921 and aged approximately 83 when tested) underwent fundus photography and the following psychometric tests: Wechsler Logical Memory, Verbal Fluency, and Raven's Standard Progressive Matrices. In addition, a general cognitive ability score (g) was obtained from these three correlated tests of cognition. The following parameters of the retinal vascular network geometry were measured: central retinal arterial and venular equivalents (CRAE and CRVE, respectively), arteriovenous ratio (AVR), suboptimality of the median branching coefficient (BC), and median angle of the five most proximal arteriolar bifurcations. General linear modeling (GLM; analysis of covariance [ANCOVA]) was used to measure associations, with gender, APOE e4 status, presence of diabetes, smoking status (current, ex-, or never), and history of cerebrovascular disease as fixed factors and the following covariables: IQ at age 11, logMAR (logarithm of the minimum angle of resolution) near visual acuity of the better-seeing eye, years of full-time formal education, occupational social class category, systolic and diastolic blood pressure, and alcohol units per week. RESULTS. Deviation of the median BC from optimality was significantly associated with general cognitive ability (g) (eta(2) = 0.034, P = 0.02) and verbal fluency (eta(2) = 0.037, P = 0.01), whereas deviation of the angle at arteriolar bifurcations from optimality was significantly associated with logical memory (eta(2) = 0.026, P = 0.03). CRAE, CRVE, and AVR did not contribute significantly to any cognitive test scores. CONCLUSIONS The association of suboptimal retinal vascular network geometry and cognition was shown in this study. It supports the concept that the retinal microvasculature acts as a surrogate marker for the cerebral microvasculature.