Change in Corneal Power Distribution in Orthokeratology: A Predictor for the Change in Axial Length

PURPOSE: To investigate the correlation between the change in spatial corneal power distribution and axial length (AL) elongation during orthokeratology (Ortho-k) treatment using mathematical methods. METHODS: Seventy-six subjects aged from eight to 13 years were fitted with Paragon CRT ortho-k lenses. Manifest refraction and corneal topography were checked at baseline and one day, one week, two weeks, one month, three months, six months, nine months, and one year after lens wear. AL was measured at baseline and the six-month and one-year follow-up visits. Relative corneal refractive power change (RCRPC) was calculated by a polynomial function and a monomial function. Factors including age, baseline spherical equivalent refractive error (SER), power exponent and RCRPC were tested against one-year AL growth in a stepwise multiple linear regression model. RESULTS: A total of 67 subjects completed the one-year study, with nine dropouts. The SER significantly reduced after the first month of lens wear (P < 0.001). AL significantly changed over time (P = 0.0003) with the annual growth being 0.32 ± 0.18 mm. Power exponent and RCRPC were stable throughout the follow-up visits (all P > 0.05). Change of AL was significantly correlated with baseline age (standardized β = −0.292, P < 0.001) and power exponent (standardized β = 0.691, P < 0.001), but not with the other factors being analyzed. The regression equation using baseline age (X(1)) and power exponent (X(2)) as functions for 1-year AL change (Y) was Y = 0.438-0.034X(1) + 0.309X(2), with R(2) being 0.752. CONCLUSIONS: The asphericity of the treatment zone may affect axial elongation in children undergoing ortho-k therapy. TRANSLATIONAL RELEVANCE: Because the ortho-k lens design may affect myopia control effect in children undergoing ortho-k therapy, future ortho-k lenses should consider applying these designs to obtain a better myopia control effect in children.