# Inter-eye Asymmetry in Refractive and Corneal Responses to Orthokeratology for Myopia Control in Rural Adolescents: A Paired-Eye Analysis

## TL;DR

This study finds that orthokeratology leads to similar eye treatment outcomes in both eyes of adolescents, making it a reliable method for controlling myopia.

## Contribution

The study provides new evidence on the consistency of orthokeratology effects in both eyes, particularly in rural adolescent populations.

## Key findings

- Orthokeratology results in minimal inter-eye asymmetry in refractive and corneal changes.
- Older age and longer treatment duration are linked to slower myopia progression.
- Baseline asymmetry and sex do not predict post-treatment asymmetry.

## Abstract

Purpose

The purpose of this study is to evaluate inter-eye asymmetry in refractive error (spherical equivalent, SE) and corneal curvature (mean keratometry, Km) following orthokeratology (ortho-k) in adolescents, and to identify clinical predictors of asymmetric treatment response using a paired-eye design.

Methods

A retrospective analysis was conducted in 53 adolescents (106 eyes; ages 8-16 years) treated with orthokeratology for at least 6 months. Absolute inter-eye differences (oculus dexter - oculus sinister (|OD−OS|)) in SE and Km were calculated at baseline and post-treatment. Paired-samples t-tests assessed inter-eye differences, Pearson correlations evaluated bilateral symmetry, and linear regression models examined predictors of post-treatment asymmetry, including baseline asymmetry, age, sex, treatment duration, and interaction terms. Generalized estimating equations were used to evaluate predictors of annualized refractive progression while accounting for inter-eye correlation.

Results

Mean baseline inter-eye asymmetry was 0.28 ± 0.34 D for SE and 0.37 ± 0.29 D for Km. Following treatment, asymmetry remained low (ΔSE: 0.22 ± 0.23 D; ΔKm: 0.15 ± 0.32 D), with no significant differences between the right and left eyes. Bilateral correlations were strong for all refractive and corneal measures. A minority of participants demonstrated higher asymmetry exceeding commonly used clinical thresholds. Linear regression analyses identified no significant predictors of post-treatment asymmetry, with low overall model explanatory power. In contrast, older age at treatment initiation and longer treatment duration were associated with slower annualized myopia progression, while baseline asymmetry and sex were not.

Conclusions

Orthokeratology produces highly symmetric bilateral refractive and corneal responses in adolescents, with minimal inter-eye asymmetry and no identifiable predictors of asymmetric outcome. The consistency of treatment effects across eyes supports orthokeratology as a reliable and predictable myopia control strategy, including in pediatric populations managed in rural or underserved settings.