title: High heritability of posterior corneal tomography, as measured by Scheimpflug imaging, in a twin study.
abstract: OBJECTIVE
  Anterior corneal curvature shows significant heritability. Scheimpflug imaging also permits assessment of posterior tomography. We estimated heritability of posterior and anterior tomographic parameters.
  
  
  METHODS
  Oculus Pentacam images were obtained in twins from the TwinsUK cohort. Mean anterior and posterior radii of curvature (right cornea) were compared within twin pairs, and heritability calculated (maximum likelihood structural equation modeling, using OpenMx package). Heritability estimates also were calculated for other parameters (anterior and posterior elevation at apex and thinnest point; pachymetry at apex and thinnest point; average pachymetry progression index).
  
  
  RESULTS
  Images from 138 twins were included (32 monozygotic [MZ] and 37 dizygotic [DZ] twin pairs). Mean (SD) age was 61 (11) years; 91% were female. Coefficients for intrapair correlation for MZ and DZ twins were, respectively, 0.89 and 0.42 for anterior curvature, and 0.93 and 0.46 for posterior curvature (P ≤ 0.0001 for differences between MZ and DZ correlations; Fisher r-to-z transformation). Heritability estimates (95% confidence interval [CI]) for anterior and posterior curvature were 89% (79%-93%) and 90% (83%-94%), respectively. Estimates for all other parameters were 75% or higher, except anterior apical elevation (61%). Point estimates for posterior parameters were consistently higher than anterior parameters, although CIs overlapped. Age-matching yielded similar estimates. Intereye correlations were high; correlations with age were weak (r < 0.30).
  
  
  CONCLUSIONS
  This is the first study to explore heritability of a number of different parameters of corneal tomography, including posterior curvature. Almost all parameters appeared highly heritable, with a trend toward higher heritability estimates for posterior (versus anterior) parameters.
authors.affiliation: Ophthalmology, King's College London, St. Thomas' Hospital Campus, London, United Kingdom.
authors.forename: Omar A
authors.initials: OA
authors.lastname: Mahroo
authors.affiliation: Ophthalmology, King's College London, St. Thomas' Hospital Campus, London, United Kingdom.
authors.forename: Mohammed
authors.initials: M
authors.lastname: Oomerjee
authors.affiliation: Ophthalmology, King's College London, St. Thomas' Hospital Campus, London, United Kingdom.
authors.forename: Katie M
authors.initials: KM
authors.lastname: Williams
authors.affiliation: Ophthalmology, Guy's & St. Thomas' NHS Foundation Trust, London, United Kingdom.
authors.forename: David P S
authors.initials: DP
authors.lastname: O'Brart
authors.affiliation: Ophthalmology, King's College London, St. Thomas' Hospital Campus, London, United Kingdom.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Hammond
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003315:Cornea / Q000473:pathology*; D019781:Corneal Topography / Q000379:methods*; D004200:Diseases in Twins / Q000175:diagnosis*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012030:Refractive Errors / Q000151:congenital / Q000175:diagnosis*; D015203:Reproducibility of Results; D014427:Twins
keywords: corneal curvature; heritability; posterior