title: Genes and environment in refractive error: the twin eye study.
abstract: OBJECTIVE
  A classical twin study was performed to examine the relative importance of genes and environment in refractive error.
  
  
  METHODS
  Refractive error was examined in 226 monozygotic (MZ) and 280 dizygotic (DZ) twin pairs aged 49 to 79 years (mean age, 62.4 years). Using a Humphrey-670 automatic refractor, continuous measures of spherical equivalent, total astigmatism, and corneal astigmatism were recorded. Univariate and bivariate maximum likelihood model fitting was used to estimate genetic and environmental variance components using information from both eyes.
  
  
  RESULTS
  For the continuous spectrum of myopia/hyperopia, a model specifying additive genetic and unique environmental factors showed the best fit to the data, yielding a heritability of 84% to 86% (95% confidence interval [CI], 81%-89%). If myopia and hyperopia (< or = -0.5 D and > or = 0.5 D, respectively) were treated as binary traits, the heritability was 90% (95% CI, 81%-95%) for myopia and 89% (95% CI, 81%-94%) for hyperopia. For total and corneal astigmatism, modeling showed dominant 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 61% of corneal astigmatism variance (95% 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; astigmatism appears to be dominantly inherited.
authors.affiliation: Twin Research and Genetic Epidemiology Unit, St. Thomas' Hospital, Lambeth Palace Road, London SE1 7EH, United Kingdom. ch@twin-research.ac.uk
authors.forename: C J
authors.initials: CJ
authors.lastname: Hammond
authors.forename: H
authors.initials: H
authors.lastname: Snieder
authors.forename: C E
authors.initials: CE
authors.lastname: Gilbert
authors.forename: T D
authors.initials: TD
authors.lastname: Spector
mesh_terms: D000368:Aged; D001251:Astigmatism / Q000235:genetics*; D004200:Diseases in Twins; D005260:Female; D006801:Humans; D006956:Hyperopia / Q000235:genetics*; D008875:Middle Aged; D009216:Myopia / Q000235:genetics*; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic