title: Heritability of myopia and ocular biometrics in Koreans: the healthy twin study.
abstract: OBJECTIVE
  To estimate the heritabilities of myopia and ocular biometrics among different family types among a Korean population.
  
  
  METHODS
  We studied 1508 adults in the Healthy Twin Study. Spherical equivalent, axial length, anterior chamber depth, and corneal astigmatism were measured by refraction, corneal topography, and A-scan ultrasonography. To see the degree of resemblance among different types of family relationships, intraclass correlation coefficients (ICC) were calculated. Variance-component methods were applied to estimate the genetic contributions to eye phenotypes as heritability based on the maximum likelihood estimation. Narrow sense heritability was calculated as the proportion of the total phenotypic variance explained by additive genetic effects, and linear and nonlinear effects of age, sex, and interactions between age and sex were adjusted.
  
  
  RESULTS
  A total of 240 monozygotic twin pairs, 45 dizygotic twin pairs, and 938 singleton adult family members who were first-degree relatives of twins in 345 families were included in the study. ICCs for spherical equivalent from monozygotic twins, pooled first-degree pairs, and spouse pairs were 0.83, 0.34, and 0.20, respectively. The ICCs of other ocular biometrics were also significantly higher in monozygotic twins compared with other relative pairs, with greater consistency and conformity. The estimated narrow sense heritability (95% confidence interval) was 0.78 (0.71-0.84) for spherical equivalent; 0.86 (0.82-0.90) for axial length; 0.83 (0.76-0.91) for anterior chamber depth; and 0.70 (0.63-0.77) for corneal astigmatism.
  
  
  CONCLUSIONS
  The estimated heritability of spherical equivalent and ocular biometrics in the Korean population suggests the compelling evidence that all traits are highly heritable.
authors.affiliation: Department of Ophthalmology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
authors.forename: Myung Hun
authors.initials: MH
authors.lastname: Kim
authors.forename: Di
authors.initials: D
authors.lastname: Zhao
authors.forename: Woori
authors.initials: W
authors.lastname: Kim
authors.forename: Dong-Hui
authors.initials: DH
authors.lastname: Lim
authors.forename: Yun-Mi
authors.initials: YM
authors.lastname: Song
authors.forename: Eliseo
authors.initials: E
authors.lastname: Guallar
authors.forename: Juhee
authors.initials: J
authors.lastname: Cho
authors.forename: Joohon
authors.initials: J
authors.lastname: Sung
authors.forename: Eui-Sang
authors.initials: ES
authors.lastname: Chung
authors.forename: Tae-Young
authors.initials: TY
authors.lastname: Chung
mesh_terms: D000328:Adult; D044466:Asian People / Q000235:genetics* / Q000706:statistics & numerical data*; D001251:Astigmatism / Q000208:ethnology* / Q000235:genetics*; D001699:Biometry; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009216:Myopia / Q000208:ethnology* / Q000235:genetics*; D010641:Phenotype; D015995:Prevalence; D012030:Refractive Errors / Q000208:ethnology / Q000235:genetics; D056910:Republic of Korea / Q000453:epidemiology; D012307:Risk Factors
keywords: heritability; myopia; twin study