Comparison of two designs of orthokeratology lenses with smaller back optic zone diameters in myopia control

Abstract

Purpose: The aim of this study was to compare and evaluate the efficacy and safety of corneal refractive therapy (CRT) and vision shaping treatment (VST) orthokeratology lenses with smaller back optical zone diameters (BOZD) in controlling myopia progression.

Methods: This retrospective study was completed from June 2019 to June 2024. A total of 1612 right eyes of myopic patients aged 8-16 years were included for analysis, and samples were categorised into four groups based on the orthokeratology lenses and their BOZD: CRT (BOZD = 6.0 mm), small BOZD CRT (CRT-S; BOZD = 5.0 mm), VST (BOZD = 6.2 mm) and small BOZD VST (VST-S, BOZD = 5.2 mm). Uncorrected visual acuity (UCVA), flat keratometry (Kf), axial length (AL) horizontal treatment zone diameter (TZD), refractive sphere (DS), refractive cylinder (DC), spherical equivalent (SE) and incidence of corneal injury were measured.

Results: Follow-up assessments were conducted until the end of the second year. The TZD of the VST-S group (1.93 ± 0.27) was significantly smaller than the CRT-S group (2.14 ± 0.21) (p < 0.001). The increase in AL in the VST-S group (0.33 ± 0.40) was significantly lower than the CRT-S group (0.44 ± 0.21) (p < 0.001). The changes in DS (-1.47 ± 0.33 vs. -1.39 ± 0.48, p = 0.01) and SE (-1.06 ± 0.77 vs. -1.62 ± 0.52, p < 0.001) in the VST-S group were significantly smaller than for the CRT-S group. No significant differences were identified in DC, UCVA and Kf changes across groups. Only a few participants exhibited corneal staining or erosion, with no significant difference between groups.

Conclusions: The myopia control effect of the VST-S lenses was significantly superior to the CRT-S lenses. Clinicians should interpret these findings cautiously when choosing smaller BOZD lenses for myopia control.

Keywords: back optical zone diameter; myopia; orthokeratology.