Prevalence of strabismus among preschool children in eastern China and comparison at a 5-year interval: a population-based cross-sectional study

OBJECTIVE: To update data on strabismus and evaluate the changes in prevalence and patterns among preschoolers in eastern China over a period of 5 years. DESIGN: Nanjing Eye Study, a longitudinal population-based study. SETTING: Recruitment and testing in kindergartens in Yuhuatai District, Nanjing. PARTICIPANTS: 2300 eligible children. MAIN OUTCOME MEASURES: Comprehensive ocular examinations were conducted in 1986 children aged 48–<60 months in Nanjing Eye Study (NES, 2016–2017), including visual acuity, ocular alignment, refractive error and ocular structures evaluation. The prevalence rate and pattern of strabismus were calculated and compared with those from the Nanjing Pediatric Vision Project (NPVP, 2011–2012) in children of the same age, of the same area and using the same diagnostic criteria. RESULTS: The overall prevalence rate of strabismus in NES was 5.56% (95% CI 4.54% to 6.57%), which was not significantly different from that in NPVP (4.99%, 95% CI 4.13% to 5.84%, p=0.40). The prevalence of subtypes of strabismus underwent significant changes, with significant increase in intermittent exotropia (IXT) in NES (2.78% vs 4.69%, p=0.001) and significant decrease in constant exotropia (1.17% vs 0.15%, p<0.001). Significant change in pattern was observed in IXT, where the proportion of the convergence insufficiency type (2.90% vs 27.17%) increased and exceeded the divergence excess type (20.29% vs 11.96%) to be the second common type (p<0.001). CONCLUSION: The prevalence of strabismus appeared stable in children aged 48–<60 months in eastern China at a 5-year interval. The prevalence of IXT increased significantly, and the convergence insufficiency type became more prevalent in patients with IXT. Timely detection and intervention of IXT are important among preschoolers.