title: Astigmatism and its determinants in the Tehran population: the Tehran eye study.
abstract: OBJECTIVE
  To determine the prevalence of astigmatism and its epidemiological risk factors in Tehran via a population-based study.
  
  
  METHODS
  By means of a stratified random cluster sampling, 6497 citizens representing a cross-section of the population of Tehran were selected from 160 clusters. Eligible people were recruited through a door-to-door household survey in the selected clusters and transferred to a clinic for an extensive eye examination and interview. The refractive status was determined with manifest refraction. Astigmatism was defined as cylinder worse than or equal to 0.5 D. High astigmatism was defined as a manifest cylinder > or =1.5 D.
  
  
  RESULTS
  Between August and December 2002, 4565 of the 6497 eligible individuals in the sample attended the interview and ophthalmic examination (a participation rate of 70.3%). The age- and gender-standardized prevalence of astigmatism was 50.2% (95% CI, 48.4% to 51.9%) on manifest refraction. High astigmatism was found in 490 right eyes (11.1%; 95% CI, 10.1% to 12.0%). Of 2532 participants with ametropia, 59.6 (95% CI, 57.6-61.5) had astigmatism. The percentages of with-the-rule, against-the-rule and oblique astigmatism were 33.6%, 36.9% and 29.3%, respectively. The proportion of type of astigmatism was significantly related to age (p < 0.001). The univariable analysis of astigmatism between family members yielded odds ratios of 1.47 (95% CI, 1.14 to 1.89, p = 0.003) for the association of astigmatism among siblings. After controlling for age, refractive errors and education, the pairwise sibling association remained statistically significant (OR 1.43, 95% CI, 1.08 to 1.88).
  
  
  CONCLUSIONS
  These findings revealed a high prevalence of astigmatism in the population. Age, education and ametropia were the main predictors of astigmatism in Tehran. Our findings should be considered for case finding and astigmatism correction programs. Our data confirmed a modest familial aggregation for astigmatism.
authors.affiliation: Farabi Eye Hospital, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran and Noor Vision Correction Center, Tehran, Iran.
authors.forename: Hassan
authors.initials: H
authors.lastname: Hashemi
authors.forename: Elham
authors.initials: E
authors.lastname: Hatef
authors.forename: Akbar
authors.initials: A
authors.lastname: Fotouhi
authors.forename: Kazem
authors.initials: K
authors.lastname: Mohammad
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000368:Aged; D000369:Aged, 80 and over; D001251:Astigmatism / Q000453:epidemiology* / Q000503:physiopathology; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007492:Iran / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D012029:Refraction, Ocular; D012189:Retrospective Studies; D012307:Risk Factors; D017678:Sex Distribution