title: Time outdoors and physical activity as predictors of incident myopia in childhood: a prospective cohort study.
abstract: OBJECTIVE
  Time spent in "sports/outdoor activity" has shown a negative association with incident myopia during childhood. We investigated the association of incident myopia with time spent outdoors and physical activity separately.
  
  
  METHODS
  Participants in the Avon Longitudinal Study of Parents and Children (ALSPAC) were assessed by noncycloplegic autorefraction at ages 7, 10, 11, 12, and 15 years, and classified as myopic (≤-1 diopters) or as emmetropic/hyperopic (≥-0.25 diopters) at each visit (N = 4,837-7,747). Physical activity at age 11 years was measured objectively using an accelerometer, worn for 1 week. Time spent outdoors was assessed via a parental questionnaire administered when children were aged 8-9 years. Variables associated with incident myopia were examined using Cox regression.
  
  
  RESULTS
  In analyses using all available data, both time spent outdoors and physical activity were associated with incident myopia, with time outdoors having the larger effect. The results were similar for analyses restricted to children classified as either nonmyopic or emmetropic/hyperopic at age 11 years. Thus, for children nonmyopic at age 11, the hazard ratio (95% confidence interval, CI) for incident myopia was 0.66 (0.47-0.93) for a high versus low amount of time spent outdoors, and 0.87 (0.76-0.99) per unit standard deviation above average increase in moderate/vigorous physical activity.
  
  
  CONCLUSIONS
  Time spent outdoors was predictive of incident myopia independently of physical activity level. The greater association observed for time outdoors suggests that the previously reported link between "sports/outdoor activity" and incident myopia is due mainly to its capture of information relating to time outdoors rather than physical activity.
authors.affiliation: School of Optometry and Vision Sciences, Cardiff University, Cardiff, Wales, United Kingdom. guggenheim@cardiff.ac.uk
authors.forename: Jeremy A
authors.initials: JA
authors.lastname: Guggenheim
authors.forename: Kate
authors.initials: K
authors.lastname: Northstone
authors.forename: George
authors.initials: G
authors.lastname: McMahon
authors.forename: Andy R
authors.initials: AR
authors.lastname: Ness
authors.forename: Kevin
authors.initials: K
authors.lastname: Deere
authors.forename: Calum
authors.initials: C
authors.lastname: Mattocks
authors.forename: Beate St
authors.initials: BS
authors.lastname: Pourcain
authors.forename: Cathy
authors.initials: C
authors.lastname: Williams
mesh_terms: D000293:Adolescent; D002648:Child; D004739:England / Q000453:epidemiology; D015444:Exercise; D005260:Female; D006801:Humans; D015994:Incidence; D053208:Kaplan-Meier Estimate; D007899:Leisure Activities; D008297:Male; D009216:Myopia / Q000453:epidemiology*; D011446:Prospective Studies; D012044:Regression Analysis; D012307:Risk Factors; D011795:Surveys and Questionnaires; D013997:Time Factors