Genes and environment in refractive error: The twin eye study

PURPOSE. A classical twin study was performed to examine the relative impor tance of genes and environment in refractive error. METHODS. Refractive error was examined in 226 monozygotic (MZ) and 280 dizy gotic (DZ) twin pairs aged 49 to 79 years (mean age, 62.4 years). Using a H umphrey-670 automatic re-fractor, continuous measures of spherical equivale nt, total astigmatism, and corneal astigmatism were recorded. Univariate an d bivariate maximum likelihood model fitting was used to estimate genetic a nd environmental variance components using information from both eyes. RESULTS. For the continuous spectrum of myopia/hyperopia, a model specifyin g additive genetic and unique environmental factors showed the best fit to the data, yielding a heritability of 84% to 86% (95% confidence interval [C I], 81%-89%). If myopia and hyperopia(less than or equal to -0.5 D and grea ter than or equal to 0.5 D, respectively) were treated as binary traits, th e heritability was 90% 85% CI, 81%-95%) for myopia and 89% (95% CI, 81%-94% ) for hyperopia. For total and corneal astigmatism, modeling showed dominan t genetic effects are important; dominant genetic effects accounted for 47% to 49% of the variance of total astigmatism (95% CI, 37%-55%) and 42% to 6 1% of corneal astigmatism variance (35% CI, 8%-71%), with additive genetic factors accounting for 1% to 4% and 4% to 18%, respectively (95% CIs, 0%-13 % and 0%-60%, respectively). CONCLUSIONS. Genetic effects are of major importance in myopia/hyperopia; a stigmatism appears to be dominantly inherited.