title: Outdoor activity and myopia among primary students in rural and urban regions of Beijing.
abstract: OBJECTIVE
  To assess associations among outdoor activity, ocular biometric parameters, and myopia among grade 1 and grade 4 primary students in Beijing.
  
  
  METHODS
  School-based, cross-sectional study.
  
  
  METHODS
  A total of 382 grade 1 and 299 grade 4 children participated in the study.
  
  
  METHODS
  The children underwent a comprehensive eye examination, including ocular biometry by optical low-coherence reflectometry and noncycloplegic refractometry. Parents and children participated in a detailed interview, including questions on time spent indoors and outdoors.
  
  
  METHODS
  Factors associated with myopia.
  
  
  RESULTS
  The study included 681 children, with 382 (56.1%) students from grade 1 (mean age, 6.3 ± 0.5 years; range, 5-8 years) and 299 students from grade 4 (mean age, 9.4 ± 0.7 years; range, 8-13 years); 370 students (54.3%) lived in the urban region. The mean daily time spent outdoors was 1.6 ± 0.8 hours (range, 0.5-5.1 hours). In multivariate analysis, axial length was significantly associated with older age (P<0.001; standardized β coefficient, 0.28), taller body height (P = 0.001; β, 0.18), maternal myopia (P = 0.03; β, 0.09), and urban region of habitation (P<0.001; β, -0.21), or alternatively to the region of habitation, with less time spent outdoors (P = 0.001; β, -0.16) and more time spent indoors studying (P = 0.02; β, 0.10). The axial length-to-corneal curvature radius ratio was associated with older age, urban region of habitation, maternal and paternal myopia, and paternal level of education. Presence of myopia (defined as refractive error ≤-1 diopters in the right eye) was associated with older age (P<0.001; odds ratio [OR], 1.45; 95% confidence interval [CI], 1.24-1.69), maternal myopia (P<0.001; OR, 2.99; 95% CI, 1.94-5.35), and urban region of habitation (P<0.001; OR, 0.17; 95% CI, 0.11-0.26), or alternatively to the region of habitation, with less time spent outdoors (P<0.001; OR, 0.32; 95% CI, 0.21-0.48) and more time spent indoors studying (P<0.001; OR, 1.38; 95% CI, 1.09-1.75).
  
  
  CONCLUSIONS
  Less outdoor activity, more indoor studying, older age, maternal myopia, and urban region of habitation were associated with longer ocular axial length and myopia in grade 1 and grade 4 primary school children in Greater Beijing. Remaining outdoors more (e.g., during school) may reduce the high prevalence of myopia in the young generation in Beijing.
authors.affiliation: Beijing Institute of Ophthalmology, Beijing Tongren Hospital, Capital Medical University, Beijing, China.
authors.forename: Yin
authors.initials: Y
authors.lastname: Guo
authors.forename: Li Juan
authors.initials: LJ
authors.lastname: Liu
authors.forename: Liang
authors.initials: L
authors.lastname: Xu
authors.forename: Yan Yun
authors.initials: YY
authors.lastname: Lv
authors.forename: Ping
authors.initials: P
authors.lastname: Tang
authors.forename: Yi
authors.initials: Y
authors.lastname: Feng
authors.forename: Meng
authors.initials: M
authors.lastname: Meng
authors.forename: Jost B
authors.initials: JB
authors.lastname: Jonas
mesh_terms: D000293:Adolescent; D058452:Axial Length, Eye / Q000473:pathology; D001699:Biometry; D002648:Child; D002675:Child, Preschool; D002681:China / Q000453:epidemiology; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007899:Leisure Activities; D008297:Male; D009216:Myopia / Q000453:epidemiology*; D012029:Refraction, Ocular / Q000502:physiology; D012424:Rural Population / Q000706:statistics & numerical data*; D013334:Students; D011795:Surveys and Questionnaires; D041623:Tomography, Optical Coherence; D014505:Urban Population / Q000706:statistics & numerical data*; D014792:Visual Acuity / Q000502:physiology