title: Astigmatism in 12-year-old Australian children: comparisons with a 6-year-old population.
abstract: OBJECTIVE
  To study the distributions of refractive (RA), corneal (CA), and internal astigmatism (IA) in 12-year-old Australian children and to explore differences from previous findings in 6-year-old children.
  
  
  METHODS
  Eligible year 7 students (2353/3144 [75.3%], median age, 12 years) from a random cluster sample of 21 high schools in Sydney, Australia, were examined by keratometry, cycloplegic autorefraction, and review of questionnaire data.
  
  
  RESULTS
  Prevalence rates of RA, CA, and IA > or =1.0 D in right eyes were 6.7% (95% confidence interval [CI], 5.0-8.4), 26.6% (CI, 22.1-31.1), and 26.5% (CI, 22.9-30.0), respectively. RA was predominantly with-the-rule (WTR; 40.4%, CI, 32.6 to 48.2) and against-the-rule (ATR; 43.6%, CI, 35.7-51.5), CA was WTR (88.8%, CI, 86.3-91.3), and IA was ATR (90.2%, CI, 87.8-92.6). The girls had significantly greater CA and IA prevalence, with greater ATR astigmatism and lower oblique IA than did the boys. The European white-Australian children had lower CA prevalence than did the East Asian-Australian children and higher IA prevalence than did the South Asian-Australian children. Ethnic differences in RA prevalence were not significant, when adjusted for confounders. RA was more frequently ATR in European white than in other ethnic groups. Compensation between CA and IA reduced the magnitude of RA. Comparison with the data on 6-year-old children revealed minimal differences for all astigmatic components.
  
  
  CONCLUSIONS
  There was a relatively low prevalence of RA, due to compensation between CA and IA. The minimal differences in all components of astigmatism between the two age cohorts suggest that astigmatism is stable between ages 6 and 12 years, although this conclusion needs to be confirmed in longitudinal studies.
authors.affiliation: Centre for Vision Research, Department of Ophthalmology and Westmead Millennium Institute, University of Sydney, Australia.
authors.forename: Son C
authors.initials: SC
authors.lastname: Huynh
authors.forename: Annette
authors.initials: A
authors.lastname: Kifley
authors.forename: Kathryn A
authors.initials: KA
authors.lastname: Rose
authors.forename: Ian G
authors.initials: IG
authors.lastname: Morgan
authors.forename: Paul
authors.initials: P
authors.lastname: Mitchell
mesh_terms: D000293:Adolescent; D001251:Astigmatism / Q000453:epidemiology*; D002648:Child; D003315:Cornea / Q000503:physiopathology; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D009517:New South Wales / Q000453:epidemiology; D015995:Prevalence; D012029:Refraction, Ocular / Q000502:physiology; D011795:Surveys and Questionnaires