title: The heritability of corneal hysteresis and ocular pulse amplitude: a twin study.
abstract: OBJECTIVE
  To examine the roles of genetic and environmental factors in corneal hysteresis and ocular pulse amplitude by performing a classic twin study.
  
  
  METHODS
  Cross-sectional twin study.
  
  
  METHODS
  Two hundred sixty-four twin pairs: 135 monozygotic (MZ) and 129 dizygotic (DZ).
  
  
  METHODS
  Corneal hysteresis was measured using the Reichert Ocular Response Analyzer (ORA; Reichert, Buffalo, NY), and ocular pulse amplitude was measured using the Pascal Dynamic Contour Tonometer (DCT; Swiss Microtechnology AG, Port, Switzerland).
  
  
  METHODS
  Contribution of genetic and environmental effects on corneal hysteresis and OPA among MZ and DZ twins.
  
  
  RESULTS
  The mean corneal hysteresis was 10.24+/-1.54 mmHg and the mean ocular pulse amplitude was 2.88+/-0.97 mmHg. The MZ correlations were higher than DZ for both corneal hysteresis and ocular pulse amplitude (correlation coefficients, 0.75:0.42 and 0.59:0.32 for MZ:DZ twins, respectively). Modeling suggested heritability of corneal hysteresis of 0.77 (95% confidence interval [CI], 0.70-0.82), with the remaining proportion of variance because of individual environmental effects of 0.23 (95% CI, 0.18-0.30). For ocular pulse amplitude, the heritability was 0.62 (95% CI, 0.51-0.70), with the remaining proportion of variance the result of individual environmental effects of 0.38 (95% CI, 0.30-0.49).
  
  
  CONCLUSIONS
  This study demonstrated that additive genetic influences explained most of the individual differences in corneal hysteresis and ocular pulse amplitude among these twins.
authors.affiliation: Twin Research and Genetic Epidemiology Unit, King's College London School of Medicine, London, United Kingdom. francis.carbonaro@btopenworld.com
authors.forename: Francis
authors.initials: F
authors.lastname: Carbonaro
authors.forename: Toby
authors.initials: T
authors.lastname: Andrew
authors.forename: David A
authors.initials: DA
authors.lastname: Mackey
authors.forename: Tim D
authors.initials: TD
authors.lastname: Spector
authors.forename: Chris J
authors.initials: CJ
authors.lastname: Hammond
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D003315:Cornea / Q000502:physiology*; D003430:Cross-Sectional Studies; D004547:Elastic Tissue / Q000502:physiology*; D004548:Elasticity; D005260:Female; D006801:Humans; D007429:Intraocular Pressure / Q000235:genetics*; D008297:Male; D008875:Middle Aged; D019655:Quantitative Trait, Heritable; D012042:Registries; D011795:Surveys and Questionnaires; D014429:Twins, Dizygotic / Q000235:genetics*; D014430:Twins, Monozygotic / Q000235:genetics*