Heritability of retinal vascular fractals: a twin study.

Abstract

Purpose : To determine the genetic contribution to the pattern or retinal vascular branching as expressed by its fractal dimension.

Methods : This was a cross-sectional study of 59 monozygotic (MZ ) and 55 dizygotic (DZ), same-gender twin pairs aged 20-46 years. In a 50-degree, disc-centred fundus photograph, the fractal dimension was evaluated by a trained grader using the box-counting method in the SIVA-Fractal software version 1.0 (National University of Singapore, Singapore). The fractal dimension was compared within MZ and DZ twin pairs using Pearson correlation coefficents. To determine the genetic component, we used Falconer’s formula to calculate the heritability, h².

Results : Retinal vascular fractals were gradable for both twins in 50 MZ and 49 DZ twin pairs. Median age was 36 years (range 20 to 46 years), and 44% were male. The mean fractal dimension was 1.505 (SD 0.0287) and 1.495 (SD 0.0324) for MZ and DZ twins, respectively. The Pearson correlation coefficient between twin A and twin B was 0.50 (p=0.0002) for MZ twins and 0.11 (p=0.46) for DZ twins. The heritability h² for the fractal dimension was 0.79.

Conclusions : The branching pattern of retinal vessels as depicted on fundus photographs of healthy young twins demonstrated a higher likeness between monozygotic twins than between dizygotic twins. The likeness parameter, fractal dimension, was determined largely by genetic factors.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.