Impact of Astigmatism on Axial Elongation in School-Age Children: A Five-Year Population-Based Study in Tianjin, China.

Purpose: To investigate the progression rates of axial length (AXL) among school-age children with baseline astigmatism and spherical ametropia. Methods: Annual vision screenings were conducted at seven schools in Tianjin, China, from 2018 to 2022. Ocular biometry and non-cycloplegic autorefraction were collected. Children 5 to 16 years old without any myopia interventions were included and categorized by their baseline astigmatism magnitude (control, low, or high) and axis orientation (with the rule [WTR], against the rule [ATR], or oblique). Additionally, children were classified by baseline spherical ametropia (compound hyperopic, compound myopic, or other). Annual AXL progression rates of right eyes were calculated using regression models and compared across different types of astigmatism and spherical ametropia. Results: A total of 10,732 Chinese children (baseline age, 9.26 ± 2.42 years; follow-up duration, 2.63 ± 1.01 years) were included and divided into a younger cohort (age < 11 years; n = 7880) and an older cohort (age ≥ 11 years; n = 2852). Across both age groups and all astigmatism magnitudes, ATR astigmatism exhibited the most rapid AXL progression, followed by oblique and WTR astigmatism. Two-way ANCOVA of the combined cohort revealed that both high-magnitude and ATR astigmatism were significantly associated with AXL progression (P ≤ 0.018). However, the impact of astigmatism on AXL progression varied depending on baseline spherical ametropia, as high-magnitude and ATR astigmatism increased AXL progression in compound myopic eyes but decreased progression in compound hyperopic eyes. Conclusions: Both baseline magnitude and axis orientation of astigmatism are significantly associated with axial elongation in children. However, these associations may vary with spherical ametropia, with differential patterns being observed between compound hyperopic and myopic eyes.