Prevalence and associated factors of strabismus and heterophoria among children and adolescents aged 3–18 years in Ningbo, Eastern China: a school-based cross-sectional study

To evaluate the prevalence and associated factors of strabismus and heterophoria among children and adolescents in Ningbo, Eastern China. A school-based eye screening examination was conducted among students aged 3 to 18 years in Ningbo, China. A total of 14,409 students from 23 randomly selected schools underwent ocular examinations including assessments of ocular alignment, uncorrected visual acuity, and non-cycloplegic refraction between September 2024 and November 2024. The prevalence of strabismus was 11.38%, comprising 11.02% with exotropia, 0.31% with esotropia, and 0.19% with vertical deviations. The prevalence of exotropia increased with age, showing an accelerated rise after age 7 and reaching approximately 14% in junior high school students and 19% in senior high school students. The prevalence rate of heterophoria was 36.40%, with 36.09% classified as exophoria and 0.31% as esophoria. The prevalence of exophoria rose rapidly during preschool years (ages 3–6) and continued to increase after school entry, albeit at a slower rate. In multivariate logistic regression analysis, exotropia was independently associated with age ≥ 8 years, myopia, astigmatism, and anisometropia (all P < 0.01). Associated factors for esotropia included female sex, hyperopia, astigmatism ≤ -2 D, anisometropia ≥ 2 D (all P < 0.01). Exophoria was significantly associated with increasing age, female sex, myopia, and anisometropia ≥ 2 D (all P < 0.05). Hyperopia and anisometropia ≥ 2 D were independently associated with esophoria (both P < 0.01). This study identified a higher prevalence of strabismus and a higher exotropia: esotropia ratio of 35.3: 1 than previous studies. These findings underscore the importance for strabismus screening, with particular focus on exotropia in junior and senior high school students and exophoria in preschool children.