Environmental and Genetic Factors Explain Differences in Intraocular Scattering.

PURPOSE: To study the relative impact of genetic and environmental factors on the variability of intraocular scattering within a classical twin study. METHODS: A total of 64 twin pairs, 32 monozygotic (MZ) (mean age: 54.9 ± 6.3 years) and 32 dizygotic (DZ) (mean age: 56.4 ± 7.0 years), were measured after a complete ophthalmologic exam had been performed to exclude all ocular pathologies that increase intraocular scatter as cataracts. Intraocular scattering was evaluated by using two different techniques based on a straylight parameter log(S) estimation: a compact optical instrument based in the principle of optical integration and a psychophysical measurement. Intraclass correlation coefficients (ICC) were used as descriptive statistics of twin resemblance, and genetic models were fitted to estimate heritability. RESULTS: No statistically significant difference was found for MZ and DZ groups for age (P = 0.203), best-corrected visual acuity (P = 0.626), cataract gradation (P = 0.701), sex (P = 0.941), optical log(S) (P = 0.386), or psychophysical log(S) (P = 0.568), with only a minor difference in equivalent sphere (P = 0.008). Intraclass correlation coefficients between siblings were similar for scatter parameters: 0.676 in MZ and 0.471 in DZ twins for optical log(S); 0.533 in MZ twins and 0.475 in DZ twins for psychophysical log(S). For equivalent sphere, ICCs were 0.767 in MZ and 0.228 in DZ twins. Conservative estimates of heritability for the measured scattering parameters were 0.39 and 0.20, respectively. CONCLUSIONS: Correlations of intraocular scatter (straylight) parameters in the groups of identical and nonidentical twins were similar. Heritability estimates were of limited magnitude, suggesting that genetic and environmental factors determine the variance of ocular straylight in healthy middle-aged adults.

The Heritability of Corneal and Ocular Higher-Order Aberrations in Koreans: The Healthy Twin Study.

PURPOSE: To estimate the genetic influences on corneal and ocular higher-order aberrations (HoAs) in the Korean population. METHODS: This was a prospective, family-based twin cohort study. A total of 1272 adult twins and their family members, who were part of the Korean Healthy Twin Study from 2007-2011, were included. Corneal and ocular HoAs were measured. The genetic influences on HoAs were investigated by using variance-component methods after adjusting for age and sex. Narrow-sense heritability was calculated. Intraclass correlation coefficients (ICCs) were used to calculate degrees of resemblance among different types of family relationships. RESULTS: A total of 269 monozygotic (MZ) twin pairs (including 176 MZ twin pairs and 93 orphan twins), 50 dizygotic (DZ) twin pairs (including 38 DZ twin pairs and 12 orphan twins), and 739 adult first-degree relatives of twins in 358 families were included. For more than half of corneal HoAs, the narrow-sense heritability estimates were not significant. Horizontal coma was highly heritable among corneal HoAs. The ICCs of horizontal coma from MZ twin pairs, pooled first-degree pairs, and spouse pairs were 0.41, 0.05, and 0.00, respectively. Among ocular HoAs, the estimated narrow-sense heritability of SA was 0.71 with the highest estimates. The ICCs of spherical aberration (SA) from MZ twins, pooled first-degree pairs, and spouse pairs were 0.76, 0.25, and 0.06, respectively. CONCLUSIONS: Both corneal and ocular HoAs demonstrated smaller heritability. Corneal HoAs showed low heritability, suggesting individual environmental factors explain most of the variance of these HoAs in the Korean population. Ocular HoAs were moderately heritable.