title: Outdoor activity reduces the prevalence of myopia in children.
abstract: OBJECTIVE
  To assess the relationship of near, midworking distance, and outdoor activities with prevalence of myopia in school-aged children.
  
  
  METHODS
  Cross-sectional study of 2 age samples from 51 Sydney schools, selected using a random cluster design.
  
  
  METHODS
  One thousand seven hundred sixty-five 6-year-olds (year 1) and 2367 12-year-olds (year 7) participated in the Sydney Myopia Study from 2003 to 2005.
  
  
  METHODS
  Children had a comprehensive eye examination, including cycloplegic refraction. Parents and children completed detailed questionnaires on activity.
  
  
  METHODS
  Myopia prevalence and mean spherical equivalent (SE) in relation to patterns of near, midworking distance, and outdoor activities. Myopia was defined as SE refraction < or = -0.5 diopters (D).
  
  
  RESULTS
  Higher levels of outdoor activity (sport and leisure activities) were associated with more hyperopic refractions and lower myopia prevalence in the 12-year-old students. Students who combined high levels of near work with low levels of outdoor activity had the least hyperopic mean refraction (+0.27 D; 95% confidence interval [CI], 0.02-0.52), whereas students who combined low levels of near work with high levels of outdoor activity had the most hyperopic mean refraction (+0.56 D; 95% CI, 0.38-0.75). Significant protective associations with increased outdoor activity were seen for the lowest (P = 0.04) and middle (P = 0.02) tertiles of near-work activity. The lowest odds ratios for myopia, after adjusting for confounders, were found in groups reporting the highest levels of outdoor activity. There were no associations between indoor sport and myopia. No consistent associations between refraction and measures of activity were seen in the 6-year-old sample.
  
  
  CONCLUSIONS
  Higher levels of total time spent outdoors, rather than sport per se, were associated with less myopia and a more hyperopic mean refraction, after adjusting for near work, parental myopia, and ethnicity.
authors.affiliation: School of Applied Vision Sciences, Faculty of Health Sciences, University of Sydney, Sydney, Australia. k.rose@usyd.edu.au
authors.forename: Kathryn A
authors.initials: KA
authors.lastname: Rose
authors.forename: Ian G
authors.initials: IG
authors.lastname: Morgan
authors.forename: Jenny
authors.initials: J
authors.lastname: Ip
authors.forename: Annette
authors.initials: A
authors.lastname: Kifley
authors.forename: Son
authors.initials: S
authors.lastname: Huynh
authors.forename: Wayne
authors.initials: W
authors.lastname: Smith
authors.forename: Paul
authors.initials: P
authors.lastname: Mitchell
mesh_terms: D002648:Child; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D006956:Hyperopia / Q000453:epidemiology; D007899:Leisure Activities; D008297:Male; D009216:Myopia / Q000453:epidemiology* / Q000208:ethnology; D009517:New South Wales / Q000453:epidemiology; D016017:Odds Ratio; D015995:Prevalence; D012029:Refraction, Ocular / Q000502:physiology; D013177:Sports; D011795:Surveys and Questionnaires; D014937:Work