Abstract
OBJECTIVE: To assess the efficacy and safety of overnight orthokeratology (Ortho-K) in patients with stable, mild-to-moderate keratoconus and myopia, with a focus on epithelial and Bowman's layer structural changes. METHODS: A prospective single-center cohort study enrolled 13 patients (24 eyes) with stable, mild-to-moderate keratoconus (Amsler-Krumeich grades I-II, age 14-21 years) who were fitted with Euclid Emerald Ortho-K lenses and followed for 18 months to evaluate clinical outcomes. Primary outcome measures included uncorrected visual acuity (UCVA), best-corrected visual acuity (BCVA), refractive error, axial length, corneal topographic parameters, corneal and corneal epithelial thickness (central, nasal, temporal), and quantitative analysis of the cross-sectional area of Bowman's layer using optical coherence tomography (OCT). Treatment-related adverse events and patient dropout were also recorded. RESULTS: After 18 months of intervention, UCVA improved significantly from logMAR 0.59 ± 0.29 to 0.19 ± 0.16 (p < 0.05). The mean myopic refraction significantly decreased from - 2.46 ± 1.25 D to - 0.62 ± 0.24 d (p < 0.05). Characteristic corneal epithelial remodeling was observed: significant thinning in the central zone (from 54 ± 9 to 41 ± 8 μm, p < 0.05) and significant thickening in the nasal and temporal zones (from 51 ± 11 to 64 ± 17 μm and from 62 ± 13 to 71 ± 9 μm, respectively; p < 0.05 for both). The key safety finding was the absence of statistically significant changes in the cross-sectional area of Bowman's layer at the nasal and temporal locations before and after treatment (p > 0.05). Axial length remained stable (mean elongation: 0.14 ± 0.13 mm, p = 0.583). Total higher-order aberrations (HOA) showed a decreasing trend that did not reach statistical significance. Five of the 18 initially enrolled patients discontinued treatment, primarily due to visual symptoms (nocturnal glare, halos) or tolerance issues (dry eye, handling difficulties). A total of 23 episodes of mild corneal punctate staining were recorded, all of which resolved completely following temporary lens discontinuation and pharmacological treatment, with no serious complications. CONCLUSION: In rigorously selected patients with stable, mild-to-moderate keratoconus, overnight orthokeratology induces predictable epithelial remodeling-characterized by central thinning and paracentral thickening-leading to significant improvements in uncorrected visual acuity and refractive stability. Critically, high-resolution OCT revealed no significant change in the cross-sectional area of Bowman's layer over 18 months, suggesting that this intervention does not compromise deep stromal structural integrity. These findings support orthokeratology as a viable, non-surgical adjunct for daytime spectacle independence in a highly selected ectatic population, provided that stringent fitting protocols and longitudinal structural monitoring are implemented.