Reliability of retinal photography in the assessment of retinal microvascular characteristics: The atherosclerosis risk in communities study

PURPOSE: Retinal microvascular characteristics, as graded from retinal photography, have been shown to predict stroke. We evaluated the reliability of retinal photographic grading in the Atherosclerosis Risk in Communities Study. DESIGN: Cohort study. METHODS: Retinal photographs were taken of all subjects who attended the third Atherosclerosis Risk in Communities Study examination (1993 to 1995). These were graded using standardized protocols. Focal retinal characteristics were graded using a "light box" system. Generalized retinal arteriolar narrowing was quantified from computer assisted measurements of digitized photographs. Two substudies were conducted to investigate the reliability of these grading methods. In the Individual Variability Study, selected subjects (n = 206) had two retinal photographs taken on one day, and a further one or two photographs taken 3 weeks later. In the Grader Variability Study, a stratified random sample of photographs had repeat retinal grading (n = 495 photographs for light box grading; n = 276 photographs for computer-assisted grading). RESULTS: Reliability of the computer-assisted quantification of generalized retinal arteriolar narrowing was high in both studies (reliability coefficients 0.64 to 0.69 for Individual Variability Study, and 0.79 to 0.83 for the Grader Variability Study). There was more variability for focal abnormalities graded using the light box system. Variability for Individual Variability Study (same individuals, repeat photographs) tended to be greater than for the Grader Variability Study (same photographs, repeat gradings). CONCLUSION: Retinal microvascular characteristics, especially computer-assisted quantification of generalized retinal arteriolar narrowing, can be ascertained reliably by standardized photographic grading methods, supporting the validity of their associations with cardiovascular disease. However, these characteristics appear to vary somewhat between eyes and over time in a single individual.