Heritability of Retinal Vascular Diameters: The Twin Eye Study

Abstract

Abstract: : Purpose: Recent work has shown that retinal vessel calibre may be a predictor of many important systemic outcomes, such as stroke. This study aimed to analyze the relative strengths of inheritance and environment on retinal vascular calibre. Methods: 506 pairs of female twins (226 monozygotic and 280 dizygotic) aged 49 to 79 years (mean 62 years) were recruited from the St Thomas' UK Adult Twin Registry. Examination included 30–degree non–simultaneous stereoscopic photographs taken with a Kowa camera using Kodak Ektachrome 64 film. Photographs were examined stereoscopically and the best stereo–pair was digitized. A computer–assisted method was used to measure average retinal arteriolar and venular diameters, summarized as the central retinal arteriolar equivalent (CRAE), central retinal venular equivalent (CRVE) and arteriole to venule ratio (AVR). Multivariate structural equation modeling was performed using Mx. Results: Retinal vessels could be graded in 196 MZ twin pairs and 255 DZ twin pairs. The case–wise concordance for mean (of the two eyes) CRAE, CRVE and AVR was 0.66, 0.73 and 0.57 in MZ pairs and 0.43, 0.44 and 0.26 in DZ pairs. The MZ/DZ risk ratios were 1.5 for CRAE, 1.6 for CRVE and 2.2 for AVR. All variables were correlated with systolic and diastolic blood pressure, and CRAE and CRVE were correlated for smoking (pack–years). Heritability estimates from multivariate modeling were 0.72 (95% CI 0.65–0.78) for CRAE, 0.78 (95% CI 0.72–0.82) for CRVE and 0.58 (95% CI 0.48–0.66) for AVR. The rest of the variation was explained by unique environment. Conclusions: These data suggest relatively strong genetic influences on retinal vessel caliber. Smoking was an important environmental influence.

Keywords: retina • clinical (human) or epidemiologic studies: risk factor assessment • blood supply