title: Distribution of radii of curvature of anterior and posterior best fit sphere in a normal population: the Tehran Eye Study.
abstract: OBJECTIVE
  To determine the distribution and determinants of the radii of curvature of the anterior and posterior best fit spheres (ABFS and PBFS) of the cornea in a sample from the general normal population of Tehran.
  
  
  METHODS
  A stratified random cluster sampling was used to select samples from the first 4 districts of Tehran proportionate to the population of each stratum. We examined the distribution of the ABFS and PBFS, as measured with the Orbscan II in different groups of age, sex, and refractive error, and determined their relationship with other variables by using both univariate and multiple regression analyses. Valid data was collected from 800 eyes, and analyses were done with data from 399 right eyes only.
  
  
  RESULTS
  Mean ABFS and PBFS in the studied sample were 43.31±1.79D and 52.67±3.04D, respectively. ABFS increased with age while PBFS showed no significant association; both showed significant inter-sex differences. In the multiple linear regression model, both ABFS and PBFS significantly correlated directly with age and average keratometry, and inversely with corneal diameter; PBFS correlated directly with anterior chamber depth as well. Mean PBFS/ABFS ratio was 1.22±0.05 which significantly decreased with age and was significantly higher in females.
  
  
  CONCLUSIONS
  Knowledge of normal ranges of ABFS and PBFS and their determinants, including age, mean keratometry, and corneal diameter, as well as the choice of measurement device, is necessary for comparing information from different populations and interpreting results.
authors.affiliation: Noor Ophthalmology Research Center, Noor Eye Hospital, Tehran, Iran.
authors.forename: Shiva
authors.initials: S
authors.lastname: Mehravaran
authors.forename: Hassan
authors.initials: H
authors.lastname: Hashemi
authors.forename: Mehdi
authors.initials: M
authors.lastname: KhabazKhoob
authors.forename: Akbar
authors.initials: A
authors.lastname: Fotouhi
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000869:Anterior Eye Segment; D015897:Comorbidity; D019781:Corneal Topography / Q000592:standards* / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D007492:Iran / Q000453:epidemiology; D007640:Keratoconus / Q000175:diagnosis* / Q000453:epidemiology*; D008297:Male; D008875:Middle Aged; D057972:Posterior Eye Segment; D012016:Reference Values; D012030:Refractive Errors / Q000175:diagnosis* / Q000453:epidemiology*; D012189:Retrospective Studies; D016008:Statistical Distributions; D055815:Young Adult