Abstract

The aim of the study was to develop an automatic segmentation approach to optical coherence tomography (OCT) images and to investigate the changes in epithelial and stromal thickness profile and radius of curvature after the use of orthokeratology (Ortho-K) contact lenses. A total of 45 right eyes from 52 participants were monitored before, and after one month of, uninterrupted overnight Ortho-K lens wear. The tomography of their right eyes was obtained using optical OCT and rotating Scheimpflug imaging (OCULUS Pentacam). A custom-built MATLAB code for automatic segmentation of corneal OCT images was created and used to assess changes in epithelial thickness, stromal thickness, corneal and stromal profiles and radii of curvature before, and after one month of, uninterrupted overnight wear of Ortho-K lenses. In the central area (0–2 mm diameter), the epithelium thinned by 12.8 ± 6.0 µm (23.8% on average, p < 0.01) after one month of Ortho-K lens wear. In the paracentral area (2–5 mm diameter), the epithelium thinned nasally and temporally (by 2.4 ± 5.9 µm, 4.5% on average, p = 0.031). The stroma thickness increased in the central area (by 4.8 ± 16.1 µm, p = 0.005). The radius of curvature of the central corneal anterior surface increased by 0.24 ± 0.26 mm (3.1%, p < 0.01) along the horizontal meridian and by 0.34 ± 0.18 mm (4.2%, p < 0.01) along the vertical meridian. There were no significant changes in the anterior and posterior stromal radius of curvature. This study introduced a new method to automatically detect the anterior corneal surface, the epithelial posterior surface and the posterior corneal surface in OCT scans. Overnight wear of Ortho-K lenses caused thinning of the central corneal epithelium. The anterior corneal surface became flattered while the anterior and posterior surfaces of the stroma did not undergo significant changes. The results are consistent with the changes reported in previous studies. The reduction in myopic refractive error caused by Ortho-K lens wear was mainly due to changes in corneal epithelium thickness profile.

Highlights

  • The prevalence of myopia has increased rapidly in recent years

  • The lines representing the corneal anterior surface, corneal posterior surface and epithelium posterior surface were displayed on the optical coherence tomography (OCT) image to enable a visual check of all the fitting processes before accepting the results or repeating parts of the analysis which produced unsatisfactory results

  • This study focused on the corneal area within 5 mm diameter because of the limitation in visible width of the epithelial surface on OCT images

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Summary

Introduction

The prevalence of myopia has increased rapidly in recent years. In 2010, there were 1950 million people with myopia globally, and the number is expected to increase to 4758 million, or 49.8% of the population, by 2050 [1]. Orthokeratology (Ortho-K) is a clinical technique that temporarily reshapes the cornea to eliminate or reduce the refractive error [2]. Earlier studies showed that Ortho-K contact lenses effectively reduce myopia, providing reliable refractive correction up to 4.5 D [5,6]. Epithelial thickness changes were recognized as the main cause of corneal reshaping [9,10,11,12,13,14,15,16]

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