Heritability of Optic Disc Morphology in the Australian Twins Eye Studies

Abstract

Abstract: : Purpose: A classical twin study was performed to determine the heritability of optic cup area, neuroretinal rim area, and total disc area, important measures in the evaluation of glaucomatous disc damage. Methods: The concordance of optic disc parameters between monozygotic (MZ) and dizygotic (DZ) twins was compared. 374 Twins (187 twin pairs; 88 MZ and 99 DZ) were recruited from the Twin Eye Study in Tasmania and the Brisbane Adolescent Twin Study. MZ twins ranged from 6 to 90 (mean 32) years of age, DZ twins ranged from 5 to 68 (mean 26). Participants underwent a comprehensive ophthalmic examination including simultaneous stereo disc photography with a Nidek 3Dx Stereo Fundus Camera. Images were digitised and analysed using a Z–screen. Custom software was used to stereoscopically plot the neuroretinal and scleral rim for each optic disc image. Cup, neuroretinal rim, and disc area were calculated for each optic disc. Structural twin heritability was analysed using the structural equation modelling package Mx. Results: The heritability of the optic disc cup area was 0.86 (95% CI 0.80 – 0.90, with environment explaining 0.14 (95% CI 0.10 – 0.21). The AE model explains the variance by additive genetic effects and unique environmental factors. The neuroretinal rim area appears to show no definite genetic effect. The ACE model for rim heritability is: 0 (95% CI 0 – 48); shared environment: 0.39 (95% CI 0 – 0.51); and individual environment: 0.61 (95% CI 0.47 – 0.74). The ACE model for total disc area heritability is: 0.27 (CI 0 – 0.60); shared environment: 0.19 (CI 0 – 0.48); and individual environment: 0.54 (95% CI 0.40 – 0.72). Conclusions: In this study of Australian twins, we found that genetic factors are of major importance in optic disc cup area, with a heritability of 0.86. Neither the neuroretinal rim area nor the total disc area showed a significant degree of heritability. Our analysis shows that the morphology of this central core is highly genetically determined. This knowledge may lead to genes being identified which may not only add to our understanding of the development of the optic nerve and retinal nerve fibre layer, but also be clinically important in pathology of this structure, such as in glaucomatous damage.

Keywords: genetics • optic disc