Abstract
Purpose:
It is known that lower order aberrations such as defocus (spherical error) and astigmatism are highly heritable. In this study, we aim to estimate the heritability of clinically relevant higher order ocular aberrations of the eye in the Caucasian population.
Methods:
Wavefront aberrometry was performed using the Shack-Hartmann method with the Visionix VX120 ocular diagnostic device on 52 dizygotic (DZ) twin pairs and 77 monozygotic twin (MZ) pairs from the TwinsUK cohort. Measurements were performed for each of the 35 Zernike terms of the left eye, the most clinically relevant terms were selected for analysis. Root Mean Squares (RMS) of Coma and Trefoil like aberrations were calculated from their constituent parts and included Trefoil X (Z33), Trefoil Y (Z3-3), and Coma X (Z31), Coma Y (Z3-1). Primary Spherical Aberration (Z40) was also included in this study. Intraclass correlation coefficients (ICC) within MZ and DZ twin pairs were obtained for the selected traits. Heritability estimates were calculated using maximum likelihood structural equation twin modelling for each trait with the OpenMX package in R. Using this method the variance of a trait is estimated by the contribution of factors; the additive genetic factors (A), the dominant genetic factors (D), the common environmental factors (C), and the unique environmental factors (E).
Results:
In this predominantly female twin cohort, the mean age was 63.3 (range: 39.7-82.5, SD 9.96). ICC between MZs and DZs were 0.40 and 0.20 for Spherical Aberration, 0.36 and 0.17 for Coma RMS, and 0.52 and 0.14 for Trefoil RMS.<br /> <br /> The most parsimonious model to explain Coma variance was AE, with a heritability estimate of 45% (95% CI 21%-63%). The best fit model to explain variance of Trefoil and Spherical Aberration was ADE, with heritability estimates of 53% and 35% respectively.
Conclusions:
In a population of older British twins, Coma, Trefoil, and Spherical Aberrations were moderately heritable. Genetic factors may contribute less to HoAs when compared to lower order aberrations such as defocus and astigmatism. Further research is needed to study whether the non-genetic effects are due to stochastic change in the eye’s aberrations, measurement error, or specific environmental factors.