Refractive Error Study in Children: sampling and measurement methods for a multi-country survey.

Purpose: 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.