Design-Dependent Myopia Control in Orthokeratology: Spherical Versus Aspherical Back Optic Zone Profiles

Background: This study examined spherical and aspherical orthokeratology (Ortho-K) lens designs for myopia control and corneal optical stability over the course of a year. Methods: This retrospective analysis used data from a previously conducted two-centre, single-blind, randomised contralateral-eye clinical study, in which 48 children aged 8 to 15 years wore a spherical Ortho-K lens in one eye and an aspherical lens in the other. Measurements included axial length (AL), best-corrected visual acuity (BCVA), lens decentration, corneal power, and higher-order aberrations over 12 months. Corneal topography was analysed using customised MATLAB code, Zernike fitting and paired inter-eye differences were evaluated with the Wilcoxon signed-rank test. Results: Both lenses exhibited typical Ortho-K reshaping patterns, with central flattening and mid-peripheral steepening. The aspherical lens resulted in slower AL elongation than the spherical lens (p < 0.01). It also produced smaller, more stable treatment zones and less variability in higher-order aberrations. Significant differences between the designs were found for vertical coma (p = 0.006), spherical aberration (p = 0.002), and vertical tilt (p = 0.02). Lens decentration also differed significantly (p < 0.01). Conclusions: Over 12 months, the aspherical Ortho-K lens demonstrated superior myopia control and more stable corneal optics than the spherical lens.