Higher-order aberrations and axial elongation in myopic children treated with orthokeratology

PURPOSE. This retrospective longitudinal study aimed to examine the relationship between ocular higher-order aberrations (HOA) and axial eye growth in young myopic children undergoing orthokeratology (ortho-k) treatment. METHODS. Axial length and ocular HOA, measured under cycloplegia annually over a 2-year period from the right eyes of myopic children, who previously completed ortho-k clinical trials, were retrieved. Linear mixed model analyses were applied to determine the association between ocular HOA, other known confounding variables (age, sex, and refractive error), and axial eye growth. RESULTS. Data from 103 subjects were analyzed. The root-mean square (RMS) values of total ocular HOA (third to sixth orders combined), spherical (Z⁰ ₄ and Z⁰ ₆ combined), and comatic (Z⁻ ₃ ¹, Z¹ ₃, Z⁻ ₅ ¹, and Z¹ ₅ combined) aberrations increased by approximately 3, 9, and 2 times, respectively, after 2 years of ortho-k treatment. After adjusting for age, sex, and refractive error, higher RMS values of total HOA and spherical aberrations were associated with both longer axial length and slower axial elongation (all P < 0.01). For individual Zernike term coefficients, a higher level of positive spherical aberration (Z⁰ ₄) was also associated with longer axial length and slower axial elongation (both P < 0.01), after adjusting for baseline HOA. CONCLUSIONS. Ortho-k for myopia control significantly increases the Zernike coefficients and therefore the RMS values for a range of total ocular HOA terms or metrics in children. These findings suggest the potential role of HOA, particularly spherical aberration, as the possible mechanism of slowing axial elongation in ortho-k treatment.