Prevalence and diagnostic signs of convergence insufficiency among schoolchildren in Kaohsiung, Taiwan: a cross-sectional study

Despite extensive global research on convergence insufficiency (CI), school-based epidemiological data in Taiwan remain scarce. This study provides the first school-based estimate of CI prevalence and diagnostic characteristics among elementary students in Kaohsiung, Taiwan. A cross-sectional school-based screening was conducted from September 2024 to January 2025 among students in grades 3–6 from public elementary schools across four administrative districts of Kaohsiung City—Gushan, Lingya, Sanmin, and Fengshan. Among the 656 initially enrolled children, 219 were included in the binocular vision assessment after excluding those with CISS scores < 16 or substandard visual acuity (n = 169). All underwent CISS evaluation and standardized binocular testing based on the Convergence Insufficiency Treatment Trial (CITT) framework. According to diagnostic criteria, CI was categorized as Low-CI (one sign), High-CI (two signs), or Definite-CI (three signs). Among 219 children, the overall prevalence of CI (≥ 1 diagnostic sign) was 35.2%, including 17.9% with Low-CI, 14.2% with High-CI, and 3.1% with Definite-CI. Girls more frequently exhibited a single CI sign—most often deficient positive fusional vergence (PFV < 15 Δ) or failing Sheard’s criterion—whereas boys showed more multiple signs. No significant grade-level differences were observed. Mean CISS scores were similar across subgroups (P = 0.985). This study provides the first school-based baseline data on convergence insufficiency (CI) among 9–12-year-old children in southern Taiwan, revealing that approximately one-third exhibited at least one CI sign with notable gender-related differences and supporting the integration of binocular vision screening into school-based vision health programs for early detection and intervention.