Ortho-K is among the most effective and consistently studied myopia control modalities. A clinician's guide to mechanism, efficacy by age, safety, and patient selection — sourced from published RCT data.
Orthokeratology (Ortho-K) uses specially designed rigid gas-permeable contact lenses worn overnight to temporarily reshape the cornea. By flattening the central cornea, the lenses induce peripheral myopic defocus — the retinal signal believed to slow axial elongation. By morning, the corneal shape produces unaided clear distance vision that lasts throughout the day without requiring daytime correction.
Beyond its role as a vision correction method, Ortho-K has accumulated the largest body of RCT evidence among contact lens modalities for myopia control. The IMI 2025 Interventions paper (Bullimore et al., IOVS 2025) identified 10 qualifying RCTs with a median 2-year axial length efficacy of 0.30mm (IQR 0.26–0.33mm) — making it consistently among the most effective modalities studied to date.
Mechanism of action: The peripheral optical effect of Ortho-K — inducing relative myopic defocus in the mid-peripheral retina — is the dominant hypothesis for why it slows axial elongation. Unlike a standard contact lens that corrects only the central refraction, Ortho-K creates a progressive power shift from the central flattened zone outward that alters how peripheral light focuses relative to the retina.
The key Ortho-K efficacy trials include the ROMIO study (Cho & Cheung, 2012), the LORIC study (Cho et al. 2005), the CONTROL study (18-month Danish RCT, Acta Ophthalmol 2022), and multiple Asian multicenter trials. A 2023 meta-analysis by Tang et al. of 7 RCTs found a weighted mean difference of −0.28mm (95% CI −0.38 to −0.19) in axial elongation at 24 months.
The IMI 2025 Interventions paper noted that Ortho-K efficacy declines with treatment duration — median 1-year benefit is 0.17mm, rising to 0.30mm at 2 years, suggesting diminishing returns per year. This pattern is distinct from some spectacle-based modalities and should factor into multi-year treatment planning discussions with families.
A 2024 systematic review and meta-analysis by Sartor et al. (Int Ophthalmol 2024) found Ortho-K reduced the rate of axial elongation vs other treatment modalities at 1 year (MD −0.16mm, 95% CI −0.25 to −0.07), and also documented that axial elongation rebounded after Ortho-K discontinuation compared with those who continued treatment (MD 0.10mm, 95% CI 0.06 to 0.14).
"Converging evidence from clinical trials demonstrates that orthokeratology is among the most effective myopia control modalities with relatively consistent results across studies. Future research should focus on identifying baseline patient characteristics to refine treatment indications, discovering biomarkers for treatment responsiveness, and optimizing lens design to enhance efficacy." — Bullimore et al., IMI 2025 Interventions Paper
The IMI 2025 Interventions paper reviewed 5 RCTs of Ortho-K combined with 0.01% atropine. Two-year results showed the combination reduced axial elongation by a median of 0.12mm more than Ortho-K alone. One 2-year randomised crossover trial (Xu et al., Br J Ophthalmol 2023) found the combination slowed axial elongation by 0.10mm in year 1 and 0.09mm in year 2. However, the IMI also noted that the effect of adding atropine decreased over time in two of the three studies, with benefits of 0.09mm in year 1 falling to 0.02mm in year 2 in one study.
Critical note: Only 0.01% atropine has been studied in combination with Ortho-K. Higher concentrations have not been evaluated in this context. The combination is most appropriate for fast progressors on Ortho-K monotherapy, not for routine first-line prescription.
The principal safety concern with Ortho-K is microbial keratitis. The Sartor et al. (2024) meta-analysis found no statistically significant difference in adverse event rates between Ortho-K and control groups (OR 2.63, 95% CI 0.72–9.61, P=0.11), though the confidence interval is wide. A frequently cited risk estimate of approximately 1 in 2,500 patient-years of wear for microbial keratitis in children is derived from Hong Kong data (Bullimore et al. 2013), which is notably lower than some earlier estimates.
The risk of microbial keratitis with Ortho-K is higher than with daily disposable soft contact lenses. Clinicians should ensure patients and parents understand overnight lens hygiene requirements and have a clear protocol for presenting to care if the eye becomes red or uncomfortable.
Sartor et al. (2024) also documented a post-discontinuation rebound in axial growth — mean 0.10mm additional growth after stopping vs continued treatment — a clinically important finding that supports discussing long-term management plans before initiating therapy.
Unlike myopia control spectacles and MiSight soft lenses — which show no significant rebound on discontinuation — Ortho-K shows some post-cessation axial length acceleration (Sartor et al. 2024: MD 0.10mm vs continued treatment). Families should be counselled on this before starting. The IMI 2025 Interventions paper notes that none of the 6 highest rebound values across all modalities were in Ortho-K studies, suggesting the rebound is modest compared to atropine.
Ortho-K is well suited to children who: want daytime glasses-free vision; participate in sports or activities incompatible with daytime correction; have myopia in the −1.00D to −5.00D range (most lenses are designed for this); are old enough to manage overnight lens wear responsibly (typically 7–8 years and above, depending on the child); and have parents committed to lens hygiene supervision.
Children with higher myopia (above −5.00D) may still benefit from Ortho-K for myopia control purposes even if incomplete optical correction is achieved. Partial correction Ortho-K still induces peripheral myopic defocus and slows axial elongation, as demonstrated in the Hong Kong ROMIO High study.