Long-term outcomes of orthokeratology in eyes with myopic regression after photorefractive keratectomy (PRK): a retrospective clinical study of 12 eyes

Background To evaluate long-term (5-year) refractive and corneal tomographic changes induced by overnight orthokeratology (OK) in eyes with myopic regression after photorefractive keratectomy (PRK), with a focus on visual efficacy, mid-peripheral alignment-based lens-fitting methodology, and corneal safety. Methods This single-center retrospective study, based on data collected between January 2016 and March 2024, included 12 eyes (nine women and three men; mean age 38.6 ± 2.9 years) with myopic regression after PRK, representing the consecutive eligible patients who continued treatment out of 15 fitted (3 discontinued for compliance-related reasons), treated with specially designed overnight OK lenses for oblate corneal profiles. Sphere, cylinder, spherical equivalent (SE), uncorrected visual acuity (UCVA), anterior and posterior keratometry at 3 mm, Mean Pupil Power (MPP), and central and thinnest corneal thickness (CCT, TCT) were assessed with a Sirius tomographer (CSO, Italy). Fitting was guided by mid-peripheral alignment zone analysis, and safety was monitored at each visit with a zero-tolerance criterion for corneal fluorescein staining. Paired differences were analysed with a Shapiro-Wilk normality test followed by a paired t-test or Wilcoxon signed-rank test as appropriate; bootstrap BCa 95% confidence intervals (B = 50,000) were computed for posterior keratometry, and effect sizes were reported as Hedges’ g. Results Mean sphere improved from −2.65 ± 0.82 D to −0.43 ± 0.28 D (p < 0.001; g = 2.57). SE improved from −3.09 ± 0.65 D to −0.76 ± 0.17 D (p < 0.001; g = 3.15). UCVA improved from 0.67 ± 0.18 to 0.05 ± 0.03 logMAR (p < 0.001; g = 3.31); 100% of patients achieved UCVA ≤ 0.10 logMAR at five years. Three parameters (cylinder, posterior K, MPP) departed from normality; paired t-test and Wilcoxon results were fully concordant for all nine parameters. Posterior K showed a mean change of +0.032 mm (Wilcoxon p = 0.021; bootstrap BCa 95% CI +0.012 to +0.068 mm), well below the ectasia threshold of 0.10 mm. No contact lens-induced corneal complications were observed during follow-up. Conclusions In this small retrospective case series, overnight orthokeratology was associated with sustained refractive and visual improvement over five years in eyes with myopic regression after PRK, and no serious adverse events were observed in these 12 patients. Effect sizes for the principal refractive and visual outcomes were large to very large; the change in cylinder was small and non-significant, and the posterior keratometry change was of medium magnitude and not clinically concerning. Given the small, uncontrolled cohort, these exploratory findings require confirmation in larger, prospective studies.