title: Heritability of spherical equivalent: a population-based twin study among 63- to 76-year-old female twins.
abstract: OBJECTIVE
  To examine the heritability of spherical equivalent (SE) in older women.
  
  
  METHODS
  Population-based twin study.
  
  
  METHODS
  Ninety monozygotic (MZ) and 86 dizygotic (DZ) female twin pairs aged 63 to 76 years who were born from 1924 through 1937.
  
  
  METHODS
  Ocular refraction was measured using an autorefractor and controlled by the subjective method. The contributions of genetic and environmental factors to individual differences in SE were estimated by applying an independent pathway model to twin data.
  
  
  METHODS
  Contribution of genetic and environmental effects to the variation in SE.
  
  
  RESULTS
  Mean SE of the study population was 1.68 (standard deviation, ± 1.82) with no differences observed either between the MZ and the DZ individuals or between the left and the right eyes. The pairwise correlations were higher in the MZ sisters (intraclass correlation coefficient [ICC], 0.803 right eye and 0.807 left eye) than DZ sisters (ICC, 0.406 right eye and 0.435 left eye). Quantitative genetic modelling showed that 83% (95% confidence interval, 77%-87%) of the variance in SE could be explained by heritable factors.
  
  
  CONCLUSIONS
  Additive genetic influences explained most of the individual differences in SE among older Finnish women.
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: Hanna-Mari
authors.initials: HM
authors.lastname: Jauhonen
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; D000375:Aging; D004185:Disability Evaluation; D005260:Female; D005387:Finland; D006801:Humans; D008875:Middle Aged; D019655:Quantitative Trait, Heritable; D012029:Refraction, Ocular / Q000235:genetics*; D014429:Twins, Dizygotic / Q000235:genetics*; D014430:Twins, Monozygotic / Q000235:genetics*