Prevalence and associations of myopia in Hong Kong primary school students

Abstract

Purpose To examine the prevalence of myopia in primary school children in Hong Kong, and the risk factors for myopia development. Study design A cross-sectional study. Methods Subjective refraction and axial length were measured in all participants. Structured questionnaire was completed by the parents to assess risk factors of myopia. Results A total of 1396 children (491 boys) from Grade 1 to Grade 6 from 4 primary schools in Sham Shui Po district of Hong Kong participated. All participants underwent non-cycloplegic refraction. The overall prevalence of myopia (spherical equivalent, SE ≤ -0.5 diopter [D]) was 37.7%, which significantly increased with age, from 13.3% at grade 1 to 54.7% at grade 6. The prevalence of moderate myopia (-3.0D < SE < -6.0D) increased from 1.6% at grade 1 to 18.2% at grade 6 and the prevalence of high myopia (SE < = -6.0 D and/or AL ≥ 26.5 mm) increased from 0.94% (7/747) in grade 1-3 students to 1.85% (12/649) in grade 4-6 students. Among the students with myopia, only 23.6% of the parents knew their children had refractive errors and only 19.8% of the children wore glasses. Multivariate logistic regression analysis showed myopia development was significantly associated with older age (OR = 1.36, P = 0.008), better academic ranking in class in the preceding semester (OR = 1.01, P = 0.02) and absence of routine eye check (OR = 2.70, P = 0.001). Conclusion The prevalence of myopia in primary school students in Hong Kong is high. There is a low level of awareness of refractive errors among parents, and high proportion of under-correction, resulting in suboptimal vision.