Regional Summed Corneal Refractive Power Changes in Myopic Orthokeratology and Their Relationships With Axial Elongation

Abstract

Purpose: To determine the relationship between regional summed corneal refractive power changes (CRPCs) in myopic orthokeratology and axial elongation. Design: This retrospective study included 70 eyes of 70 patients aged 8 years to 13 years who underwent orthokeratology lens (OK lens) treatment, and all patients underwent regular follow-ups at 1 week, 1 month, 6 months, and 12 months at Zhongshan Ophthalmic Center between January 2019 and May 2021. Methods: Axial length (AL) was measured at baseline and 12 months by an IOLmaster 5.0. Refractive error power was measured using cycloplegia. Regional summed CRPCs were calculated by MATLAB software using difference tangential power maps at the sixth month acquired by corneal topography measurements (Medmont E300 Corneal Topographer; Medmont Pty, Victoria, Australia) and defined as changes in corneal refractive power at the sixth month from baseline. The regional summed CRPCs were then subdivided into 4-mm diameter circles, 4- to 5-mm diameter chords, and 5- to 6-mm diameter chords according to the distance from the central of the pupil and into negative, positive, and total according to the values. Pearson correlation, multiple linear regression analysis, and stepwise multiple linear regression analysis were performed to analyze the relationships among these parameters. Results: Axial elongation had a negative relationship with positive regional summed corneal refractive power in the central 4-mm diameter circle and age (r=−0.282, P=0.018; r=−0.473, P<0.001, respectively) and a positive relationship with negative regional summed corneal refractive power in the 5- to 6-mm diameter chord (r=0.361, P=0.002). Stepwise multiple linear regression analysis identified age (standardized β=−0.434, P<0.001) and negative regional summed corneal refractive power in the 5- to 6-mm diameter chord (standardized β=0.305, P=0.004) as factors influencing AL elongation. Conclusion: Negative regional summed corneal refractive power in a 5- to 6-mm diameter chord after OK lens treatment may be an important index for evaluating the control effects of axial elongation.