title: Characteristics of astigmatism in a population of schoolchildren, Dezful, Iran.
abstract: OBJECTIVE
  To study and analyze astigmatism and its characteristics in a cross-sectional study of schoolchildren from Dezful, Iran.
  
  
  METHODS
  In a cross-sectional study using random cluster sampling on 460 schools in Dezful (clusters), 39 clusters were selected. The study was conducted after coordinating with schools and obtaining written consent from students' parents. Cycloplegic refraction was done for primary and junior high school students and non-cycloplegic refraction was done for high school students. Astigmatism was defined as the cylinder power of 0.75 diopter (D) or more.
  
  
  RESULTS
  Of 5726 selected students, 5544 (96.8%) participated in the study. The prevalence of astigmatism was 13.47% (95% confidence interval: 11.90 to 15.04) and was not significantly related to age and gender. Regarding axis, 45.76, 48.14, and 6.09% of astigmatic schoolchildren had with-the-rule (WTR), against-the-rule (ATR), and oblique astigmatism, respectively. An increase in age was accompanied by a decrease in the prevalence of WTR astigmatism and an increase in the prevalence of ATR astigmatism (p < 0.001). The association between astigmatism and myopia [odds ratio = 8.81] was stronger than its association with hyperopia (odds ratio = 3.81). Those with high values of spherical error had high values of cylindrical error, as well. Mean sphere in WTR, ATR, and oblique astigmatism was 1.93, 1.37, and 0.88 D, respectively (p < 0.001). The highest values of spherical refractive error were observed in WTR astigmatism group.
  
  
  CONCLUSIONS
  The prevalence of ATR astigmatism was high in this study. It appears that the decrease in the prevalence of WTR and the increase in the prevalence of ATR astigmatism as a result of aging happened earlier in our study compared with other studies. Astigmatism was found to have a strong correlation with myopia, although individuals with high hyperopia also had high astigmatism. Individuals with high ametropia mostly had WTR astigmatism although the percentage of ATR astigmatism was high in those with low ametropia.
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran. afotouhi@tums.ac.ir
authors.forename: Akbar
authors.initials: A
authors.lastname: Fotouhi
authors.forename: Hassan
authors.initials: H
authors.lastname: Hashemi
authors.forename: Abbas Ali
authors.initials: AA
authors.lastname: Yekta
authors.forename: Kazem
authors.initials: K
authors.lastname: Mohammad
authors.forename: Mehdi Khabaz
authors.initials: MK
authors.lastname: Khoob
mesh_terms: D000293:Adolescent; D017677:Age Distribution; D000375:Aging / Q000502:physiology*; D001251:Astigmatism / Q000175:diagnosis / Q000453:epidemiology* / Q000503:physiopathology; D002648:Child; D016000:Cluster Analysis; D016001:Confidence Intervals; D003430:Cross-Sectional Studies; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007492:Iran / Q000453:epidemiology; D008297:Male; D016017:Odds Ratio; D015995:Prevalence; D011379:Prognosis; D012029:Refraction, Ocular; D012189:Retrospective Studies; D017678:Sex Distribution; D014787:Vision Tests; D055815:Young Adult