Myopic Shift Accelerates at Refractive Diopter Below +1.0 in Children Aged 6 to 9 Years Old

The rate of myopic shift (known as refractive progression) is known to be higher in myopic children compared to their nonmyopic peers. This study aims to explore if there exists a critical range of baseline refraction over which myopic shift accelerates.

A secondary analysis of a school-based cluster-randomized trial (Shanghai Time Outside to Reduce Myopia, STORM), with external validation.

Data from participants who had complete data from at least 2 consecutive visitsand were not myopic in both eyes at the initial visit were included. Myopic shift over a 1-year period was calculated as the difference between the initial spherical equivalent (SE) and the SE measured 1 year later. Ocular parameters were collected including cycloplegic refraction, axial length (AL) and lens power (LP). Multivariable linear regressions and restricted cubic spline (RCS) analysis were conducted to assess the relationship between baseline spherical equivalent (SE) and 1-year change in SE (ΔSE), AL(ΔAL) and LP (ΔLP) by adjusting covariates. Appropriate turning points were evaluated by Akaike's information criterion (AIC) and Bayesian information criterion (BIC) from the segmented regression model. Sensitivity analysis and an independent validation analysis were performed.

A total of 4,220 children were included, with a mean age of 7.2 (SD, 0.6) years and 50.5% boys. The mean 1-year ΔSE, ΔAL, and ΔLP were -0.36 ± 0.43 D, 0.24 ± 0.22 mm, and 0.22 ± 3.26 D, respectively. In the RCS analysis, 1-year ΔSE accelerated when baseline SE dropped below +1.0 D, but remained stable when baseline SE was above +1.0 D, indicating a turning point at a SE of +1.0 D (P for linearity <0.001). The nonlinear relationship between baseline SE and 1-year ΔSE was consistent across all age groups, with baseline SE turning points around +1.0 D. The lowest AIC for 1-year ΔSE occurred at a baseline SE of +1.00 D, while for 1-year ΔAL, it was +1.25 D, and for 1-year ΔLP, it was +1.50 D. Sensitivity and validation analyses confirmed the turning point of baseline SE on 1-year ΔSE around +1.0 D.

This study found that myopic shift accelerated at SE below +1.0 D among children aged 6 to 9 years. This helps to define the range of refractions over which children are at higher risk of subsequent development of myopia.