Axial length to corneal curvature ratio moderates the effect of corneal reshaping on axial growth in orthokeratology

Purpose: To evaluate the association between summed relative corneal refractive power (sRCRP) and age-adjusted axial length growth (aALG) in children undergoing orthokeratology (OK), and to determine whether this relationship is moderated by the axial length to corneal curvature (AL/K) ratio. Methods: This retrospective study included 318 eyes of children (8–13 years of age) treated with OK lens for 1 year. Corneal curvature (CC) was quantified using mean keratometry (K) values, and the AL/K ratio was used to represent baseline ocular structure. Axial length growth (ALG) over 1 year was adjusted for age (aALG). sRCRP was derived from 1-year axial maps within the central 4 mm. Associations between sRCRP and aALG were assessed by multiple linear regression, with moderation assessed via interaction terms, simple slopes analysis and the Johnson–Neyman technique. Results: The mean sRCRP was 19.39 ± 10.29 D·mm² and the mean aALG was −0.07 ± 0.21 mm after 1 year. Multivariate regression showed that sRCRP (β = −0.01, p < 0.001), baseline AL (β = −0.09, p < 0.001) and spherical equivalent refraction (β = −0.02, p = 0.03) were significant predictors of aALG. A significant interaction between sRCRP and AL/K ratio (β = 0.10, p = 0.01) indicated that the effect of sRCRP on aALG varied with baseline ocular structure. Johnson–Neyman analysis revealed that sRCRP was significantly associated with reduced aALG only when the AL/K ratio was below 0.61. Conclusions: The AL/K ratio moderates the relationship between sRCRP and myopia control efficacy in OK lens treatment. sRCRP is predictive of treatment outcome primarily in eyes with lower AL/K ratios, supporting the role of biometric profiling in guiding individual OK lens strategies.