title: Refractive Error Study in Children: sampling and measurement methods for a multi-country survey.
abstract: OBJECTIVE
  The Refractive Error Study in Children was designed to assess the prevalence of refractive error and vision impairment in children of different ethnic origins and cultural settings.
  
  
  METHODS
  Population-based cross-sectional samples of children 5 to 15 years of age were obtained through cluster sampling. Presenting, uncorrected, and best-corrected visual acuity, along with refractive error under cycloplegia, were the main outcome measures. Amblyopia and other causes of uncorrectable vision impairment were determined.
  
  
  RESULTS
  Study design and sample size calculations, survey enumeration and ophthalmic examination methods, quality assurance monitoring, and da ta analyses and statistical methods are described.
  
  
  CONCLUSIONS
  The study design, sample size, and measurement methods ensure that the prevalence of age-specific and sex-specific refractive error can be estimated with reasonable accuracy in the target populations. With commonality of methods, a comparison of findings between studies in different ethnic origins and cultural settings is possible.
authors.affiliation: Programme for the Prevention of Blindness and Deafness, World Health Organization, Geneva, Switzerland.
authors.forename: A D
authors.initials: AD
authors.lastname: Negrel
authors.forename: E
authors.initials: E
authors.lastname: Maul
authors.forename: G P
authors.initials: GP
authors.lastname: Pokharel
authors.forename: J
authors.initials: J
authors.lastname: Zhao
authors.forename: L B
authors.initials: LB
authors.lastname: Ellwein
mesh_terms: D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D002677:Chile / Q000453:epidemiology; D002681:China / Q000453:epidemiology; D003430:Cross-Sectional Studies; D004812:Epidemiologic Methods; D005260:Female; D006306:Health Surveys; D006801:Humans; D008297:Male; D009390:Nepal / Q000453:epidemiology; D015995:Prevalence; D012030:Refractive Errors / Q000208:ethnology*; D012494:Sampling Studies; D014786:Vision Disorders / Q000208:ethnology*; D014792:Visual Acuity