title: Central corneal thickness is highly heritable: the twin eye studies.
abstract: OBJECTIVE
  A classic twin study was performed to determine the heritability of central corneal thickness (CCT), an important parameter in glaucoma assessment.
  
  
  METHODS
  The concordance of CCT between monozygotic (MZ) and dizygotic (DZ) twins was compared. A total of 256 twin pairs (131 MZ and 125 DZ) were recruited from three centers: the Twin Eye Study in Tasmania, the Brisbane Adolescent Twin Study, and the Twins U.K. Adult Registry held at St. Thomas' Hospital in London. As part of an extensive ophthalmic evaluation, CCT was measured by ultrasound pachymetry. Structural equation modeling with the Mx program (Department of Psychiatry, Medical College of Virginia, Richmond, VA) was used to determine the heritability of CCT.
  
  
  RESULTS
  The mean age of subjects was 38 years (range, 8-81). The mean CCT of all eyes examined was 544.5 +/- 37.3 mum (SD). The CCT measurements correlated more highly in MZ twins than in DZ twins, with intraclass correlation coefficients of 0.95 and 0.52, respectively, suggesting a strong genetic influence. A model of additive genetic and unique environmental effects provided the best fit, yielding a heritability of 0.95 (95% confidence interval [CI], 0.93-0.96) with the remaining variation being attributable to unique environmental factors.
  
  
  CONCLUSIONS
  In this study of Australian and U.K. twins, genetic factors were shown to be of major importance in CCT, with a heritability of 0.95.
authors.affiliation: University of Tasmania, The Eye Hospital, Launceston, Australia.
authors.forename: Tze'Yo
authors.initials: T
authors.lastname: Toh
authors.forename: S H Melissa
authors.initials: SH
authors.lastname: Liew
authors.forename: Jane R
authors.initials: JR
authors.lastname: MacKinnon
authors.forename: Alex W
authors.initials: AW
authors.lastname: Hewitt
authors.forename: Johan L
authors.initials: JL
authors.lastname: Poulsen
authors.forename: Tim D
authors.initials: TD
authors.lastname: Spector
authors.forename: Clare E
authors.initials: CE
authors.lastname: Gilbert
authors.forename: Jamie E
authors.initials: JE
authors.lastname: Craig
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Hammond
authors.forename: David A
authors.initials: DA
authors.lastname: Mackey
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000886:Anthropometry; D002648:Child; D003315:Cornea / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D003941:Diagnostic Techniques, Ophthalmological; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D014429:Twins, Dizygotic / Q000235:genetics*; D014430:Twins, Monozygotic / Q000235:genetics*; D014463:Ultrasonography