Aims: The aim of this study was to describe the heritability of retinal vessel diameter in complex pedigrees of a Flemish population. We also investigated genetic and environmental correlations of retinal microvascular phenotypes.

Methods: In 413 participants from 70 families (mean age 51.5 years; 50.1% women), randomly recruited from a Flemish population, we post-processed retinal images using IVAN software to generate the central retinal arteriole and venule equivalents (CRAE and CRVE) and the arteriole-to-venule-ratio (AVR). We used S.A.G.E. Statistical Analysis to estimate heritability and to calculate the genetic and environmental correlations.

Results: In multivariable-adjusted analyses, CRAE decreased with age and mean arterial pressure, and was higher in women than in men. CRVE decreased with mean arterial pressure. Current smokers had higher CRAE and CRVE. These common cardiovascular risk factors only explained 12.7% and 7.3% of the total variance of CRAE and CRVE, respectively. With adjustments applied for these covariables, the heritability estimates of CRAE, CRVE, and AVR were 0.213 (P=0.044), 0.339 (P=0.010) and 0.272 (P=0.004), respectively. The genetic correlation was 0.360 (P<0.0001) between CRAE and CRVE.

Conclusions: Retinal microvascular phenotypes play an important role in prediction of cardiovascular disease. However, traditional cardiovascular risk factors explained only a little of the variance of retinal microcirculation. Our study showed moderate heritability for CRAE, CRVE and AVR, and significant genetic correlation between CRAE and CRVE in a Flemish population. This suggested that genetic variants might play an important role in the association between retinal diameter and cardiovascular disease.