title: Heritability of corneal refraction and corneal astigmatism: a population-based twin study among 66- to 79-year-old female twins.
abstract: OBJECTIVE
  To examine the heritability of corneal refraction power (CR) and corneal astigmatism (AST) in older women.
  
  
  METHODS
  Corneal refraction and AST were measured by IOL master in 52 monozygotic (MZ) and 47 dizygotic (DZ) female twin pairs aged 66-79 years. The relative contribution of genetic and environmental factors to individual differences in CR was estimated by applying an independent pathway model to the twin data and AST by intraclass correlations (ICC).
  
  
  RESULTS
  For the right eye, mean CR was 44.58 dioptres (D) (standard deviation (SD) ±1.28) When comparing CR of the right and left eye between MZ and DZ, no significant difference was found. Mean AST was 0.77 D (SD ±0.44) with no differences observed either between the MZ and the DZ individuals, or between the left and the right eyes. ICCs between the sisters for CR were, for the right eye, 0.882 and 0.378 for MZ and DZ, respectively, and for the left eye 0.855 and 0.358. For AST of the right eye, the ICCs were 0.533 and 0.096 for the MZ and DZ pairs, respectively, and for the left eye, the MZ and DZ correlations were 0.396 and 0.299. Quantitative genetic modelling showed that 81% of the variance in CR could be explained by genetic factors, additive genetic factors explaining 62% (95% confidence interval [CI] 44% -86%) and dominant genetic effect 19% (95% CI 7-49%) of the variance in CR. Different models were constructed to explain the heredity of AST. None of these models gave meaningful results, although the ICC values for MZ were higher than those for DZ.
  
  
  CONCLUSIONS
  Most of the variance in CR among older Finnish women could be explained by genetic factors.
authors.affiliation: Department of Ophthalmology, Central Hospital of Central Finland, Jyväskylä, Finland. olavi.parssinen@top.fimnet.fi
authors.forename: Olavi
authors.initials: O
authors.lastname: Pärssinen
authors.forename: Markku
authors.initials: M
authors.lastname: Kauppinen
authors.forename: Jaakko
authors.initials: J
authors.lastname: Kaprio
authors.forename: Markku
authors.initials: M
authors.lastname: Koskenvuo
authors.forename: Taina
authors.initials: T
authors.lastname: Rantanen
mesh_terms: D000368:Aged; D001251:Astigmatism / Q000235:genetics*; D004200:Diseases in Twins / Q000235:genetics*; D005260:Female; D005387:Finland; D059647:Gene-Environment Interaction; D006801:Humans; D040582:Inheritance Patterns; D008957:Models, Genetic; D012029:Refraction, Ocular / Q000235:genetics*; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic; D044465:White People / Q000235:genetics