Objective: To investigate the axial length (AL) elongation in primary school-age children during 3-year follow-up period, and evaluate the associations of AL elongation with spherical equivalent (SE), AL at baseline, body height and weight.

Design: A 3-year observational cohort study from 2014 to 2017.

Setting: Jinshan Hospital of Fudan University in Shanghai.

Methods: A total of 452 children successfully completed their measurements in the 3-year follow-up period. Among those children, the mean age was 6.9 ± 0.7 years, ranging from 6 years to 8 years, and 217 (42.7%) were boys. AL was measured with an ocular biometry system. Refractive error was measured using an auto-refractor without cycloplegia.

Results: The mean changes of ALs were 0.27 ± 0.28 mm, 0.52 ± 0.40 mm, and 0.89 ± 0.51mm over 1 year, over 2 years and over 3 years, respectively. The mean changes of Spherical equivalents (SEs) were -0.27 ± 0.80 D, -0.56 ± 1.00 D, and -0.95 ± 1.41 D over 1 year, over 2 years and over 3 years, respectively. Multivariate linear regression analysis revealed that mean change of AL was associated with mean change of SE at all points (all P < 0.001). In addition, linear regression analysis revealed that AL elongation in the 3-year follow-up period was associated with AL at baseline (R2 = 0.009, P = 0.045).

Conclusions: AL elongation is relatively high in the primary school-age children in Jinshan District, Shanghai. Effect strategies are needed to control AL elongation.