Purpose: To investigate changes in relative peripheral refraction (RPR) and their associations with axial length (AL) growth after one year of orthokeratology (ortho-k) therapy.

Methods: This prospective cohort study included 60 myopic children aged 8-15 years. RPR and AL were measured at baseline and 12 months after ortho-k therapy. Total RPR was measured via multispectral refraction topography (MRT) in the 53° fundus field of view, and then was divided into specific annuli (0-10°, 10-20°, 20-30°, 30-40°, 40-50° and 50-53°) and quadrants (superior, inferior, temporal and nasal). Linear regression analyses quantified associations between RPR changes and AL elongation.

Results: Ultimately, 80.0% of the participants were analysed. The total RPR was 0.64 ± 0.26 D at baseline and -0.35 ± 0.64 D at 12 months. Ortho-k therapy induced myopic shifts in all subregions (all p < 0.05). Additionally, hyperopic RPRs within the 50° region and in the superior, inferior and nasal parts of the retina became myopic. These myopes had an asymmetric RPR in the vertical retina both before and after ortho-k treatment but a symmetric RPR in the horizontal retina, which changed after treatment. Multivariate linear regression analyses revealed that the baseline AL and RPR changes in the 30-40° region and in the inferior retina were independently associated with AL elongation during one-year of ortho-k lens wear (all p < 0.05).

Conclusions: The more myopic shifts of RPR induced by ortho-k treatment in the 30° to 40° region and in the inferior retina, the more effective control of axial elongation.