title: Determinants and heritability of intraocular pressure and cup-to-disc ratio in a defined older population.
abstract: OBJECTIVE
  To investigate the heritability of intraocular pressure (IOP) and cup-to-disc ratio (CDR) in an older well-defined population.
  
  
  METHODS
  Family-based cohort study.
  
  
  METHODS
  Through the population-based Salisbury Eye Evaluation study, we recruited 726 siblings (mean age, 74.7 years) in 284 sibships.
  
  
  METHODS
  Intraocular pressure and CDR were measured bilaterally for all participants. The presence or absence of glaucoma was determined by a glaucoma specialist for all probands on the basis of visual field, optic nerve appearance, and history. The heritability of IOP was calculated as twice the residual between-sibling correlation of IOP using linear regression and generalized estimating equations after adjusting for age, gender, mean arterial pressure, race, self-reported diabetes status, and history of systemic steroid use. The heritability of CDR was calculated using the same model and adjustments as above, while also adjusting for IOP.
  
  
  METHODS
  Heritability and determinants of IOP and CDR, and impact of siblings' glaucoma status on IOP and CDR.
  
  
  RESULTS
  We estimated the heritability to be 0.29 (95% confidence interval [CI], 0.12-0.46) for IOP and 0.56 (95% CI, 0.35-0.76) for CDR in this population. Mean IOP in siblings of glaucomatous probands was statistically significantly higher than in siblings of normal probands (mean difference, 1.02 mmHg; P = 0.017). The mean CDR in siblings of glaucomatous probands was 0.07 (or 19%) larger than in siblings of glaucoma suspect referrals (P = 0.045) and siblings of normal probands (P = 0.004).
  
  
  CONCLUSIONS
  In this elderly population, we found CDR to be highly heritable and IOP to be moderately heritable. On average, siblings of glaucoma patients had higher IOPs and larger CDRs than siblings of nonglaucomatous probands.
authors.affiliation: Dana Center for Preventive Ophthalmology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
authors.forename: Ta C
authors.initials: TC
authors.lastname: Chang
authors.forename: Nathan G
authors.initials: NG
authors.lastname: Congdon
authors.forename: Robert
authors.initials: R
authors.lastname: Wojciechowski
authors.forename: Beatriz
authors.initials: B
authors.lastname: Muñoz
authors.forename: Donna
authors.initials: D
authors.lastname: Gilbert
authors.forename: Ping
authors.initials: P
authors.lastname: Chen
authors.forename: David S
authors.initials: DS
authors.lastname: Friedman
authors.forename: Sheila K
authors.initials: SK
authors.lastname: West
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D044383:Black People / Q000235:genetics; D015331:Cohort Studies; D005260:Female; D005902:Glaucoma, Open-Angle / Q000453:epidemiology / Q000235:genetics*; D006801:Humans; D007429:Intraocular Pressure / Q000235:genetics*; D008297:Male; D008396:Maryland / Q000453:epidemiology; D009898:Optic Disk / Q000473:pathology*; D009901:Optic Nerve Diseases / Q000453:epidemiology / Q000235:genetics*; D035781:Siblings; D044465:White People / Q000235:genetics; D001741:Black or African American