The influence of age in the progression from pre-myopia to myopia onset: a 1 year retrospective analysis

Pre-myopia is a critical stage before myopia onset, yet little is known about how age influences axial elongation during the transition from pre-myopia to myopia. This study aimed to investigate the effect of age on annual axial elongation during this 1 year conversion period.

This retrospective study included 53 children (53 right eyes) aged 6-10 years who progressed from pre-myopia (spherical equivalent refraction ≤ + 0.75 D and > - 0.50 D) to myopia (≤ - 0.50 D) within 1 year. Annual axial elongation (ΔAL) was calculated as the absolute change in axial length over 1 year. Analysis of covariance (ANCOVA) was performed with ΔAL as the dependent variable, age group (6-9 years) as a fixed factor, and baseline axial length and baseline spherical equivalent refraction as covariates. Pairwise comparisons were adjusted using the Bonferroni method. Age was further dichotomized into 6-7 years and 8-9 years for subgroup analysis, and also analyzed as a continuous variable using multiple linear regression.

Annual axial elongation decreased with increasing age: 0.76 ± 0.16 mm (6y), 0.64 ± 0.17 mm (7y), 0.54 ± 0.24 mm (8y), 0.37 ± 0.14 mm (9y), and 0.38 ± 0.03 mm (10y). After adjusting for baseline ocular biometrics, ANCOVA revealed a significant main effect of age on ΔAL [F(3, 45) = 3.689, p = 0.019, partial η² = 0.197]. Bonferroni-corrected comparisons showed that children aged 6 and 7 years exhibited significantly greater axial elongation than those aged 9 years (mean differences = 0.391 mm and 0.271 mm, respectively; both p < 0.01). In the dichotomized comparison, the 6-7-year group had significantly greater ΔAL than the 8-9-year group (0.653 mm vs. 0.499 mm, p = 0.009). When analyzed as a continuous predictor, each additional year of age was associated with a 0.093 mm decrease in annual axial elongation [β = -0.093, 95% CI (-0.150, -0.035), p = 0.002].

Among children who converted from pre-myopia to myopia within 1 year, younger age was associated with greater axial elongation. These findings highlight the importance of early surveillance and preventive strategies in the pre-myopic stage, particularly for children aged 6-7 years. Larger prospective studies controlling for environmental and familial risk factors are needed.