Adiposity and the Prevalence, Incidence and Distribution of Refractive Errors in Urban Vietnamese Children

Abstract

Purpose: To examine the association between BMI-for-age z-score (BAZ) and BMI status with refractive error prevalence, incidence, subtypes, and quantitative refraction in Vietnamese schoolchildren. Methods: We retrospectively analyzed body mass index and refractive error data from annual school health checks in three Vietnamese cities, 2022 to 2024. The main analysis set was restricted to children age 6 and older (49,415 examinations, 31,522 children). Refractive error subtypes and quantitative refraction came from a Hanoi autorefractor sub-cohort (13,059 examinations). We used sex-stratified Poisson models with generalized estimating equations, adjusted for age, city, and year, plus linear mixed models for quantitative outcomes. Results: Any refractive error followed a U shaped curve across BAZ in both sexes, significant in girls (prevalence ratio 1.01 per 1-SD BAZ, p = 0.027) but not boys (p = 0.099). Obesity was associated with higher any refractive error prevalence in girls (adjusted prevalence ratio 1.05, p = 0.017). Astigmatism was associated with BAZ in both sexes (p < 0.001), anisometropia in boys only (p < 0.001), with no association for myopia or hyperopia. Spherical equivalent shifted slightly toward hyperopia, not myopia, with higher BAZ. A supplementary check over 1 to 2 years found no evidence that prior BAZ predicted new refractive error onset (prevalence ratio 1.02, p > 0.6 in both sexes), and the nonlinear pattern did not reappear. Conclusions: Adiposity relates cross-sectionally to refractive error in a nonlinear, sex specific way concentrated in astigmatism and anisometropia rather than myopia, though this did not hold up short term.