What Is Ortho-K?
Orthokeratology (often called Ortho-K, OK, overnight corneal refractive therapy, or corneal reshaping) is a non-surgical method to temporarily correct refractive errors (especially myopia) by using specially designed rigid gas permeable (RGP) contact lenses worn overnight.
These lenses gently reshape the central corneal curvature while you sleep. Upon removal in the morning, the cornea retains that modified shape for a period of time, allowing improved unaided vision during waking hours.
Because the effect is reversible, Ortho-K must be maintained via periodic lens wear. If lens wear is discontinued, the cornea gradually returns to its original shape and the refractive error returns.
Mechanism & Indications
How It Works
- The posterior surface of an Ortho-K lens is designed with a reverse geometry shape: a flatter central zone and steeper zones around it. This creates a controlled redistribution of epithelial cells and corneal tissue to flatten the central cornea and steepen the mid-periphery. (Lippincott Journals)
- The flattening decreases the myopic refractive power, pushing the focal point closer to or on the retina.
- Typical approved parameters allow correction up to about –6.00 diopters of myopia, and some lenses allow limited amounts of astigmatism (e.g., Paragon CRT up to ~1.75 D) for overnight wear. (FDA Access Data)
Primary Uses
- Myopia correction (especially mild to moderate cases) in those who prefer to avoid daytime glasses or contacts. (U.S. Food and Drug Administration)
- Myopia control in children: Ortho-K has been shown in multiple studies to slow the progression of axial elongation in myopic children compared to single vision lenses. (PubMed)
- Situations where daytime glasses or contacts are inconvenient (e.g., sports).
Effectiveness & Evidence
- A meta-analysis comparing Ortho-K across studies found that it can reduce the elongation of the axial length (a marker of myopia progression) by approximately 32% to 63% over 2 years relative to standard correction. (PubMed)
- Another systematic review of benefits and risks summarized that Ortho-K is a viable option with acceptable safety if well managed. (PMC)
- A study on children wearing OK lenses revealed improved optical parameters (MTF cutoff, Strehl ratio) over the first month, with stabilization over 3 months. Though optical quality may initially degrade, visual performance remained mostly unchanged. (Frontiers)
- Regarding safety, a broad review of ~170 publications found that the most common complications were corneal staining, with microbial keratitis risk in overnight Ortho-K being comparable to other overnight lens modalities. No long-term damage to corneal endothelium was demonstrated in the reviewed literature. (Lippincott Journals)
Risks & Considerations
- Microbial keratitis (infection of the cornea) is the most serious risk, especially with overnight wear and lapses in hygiene. (Lippincott Journals)
- Corneal staining, epithelial defects, or changes in corneal biomechanics may occur. (Lippincott Journals)
- Optical aberrations, glare, halos, or decreased contrast sensitivity may happen, particularly early in treatment. (Frontiers)
- Decentration (lens misalignment on the cornea) is a risk; interestingly, moderate decentration (≤ 1.5 mm) may not reduce myopia control efficacy, if visual acuity remains acceptable. (Pediatric Medicine)
To maximize safety, success depends heavily on correct lens fitting, strict adherence to lens care protocols, scheduled follow-ups, and prompt handling of complications. (Lippincott Journals)
Practical Use & Maintenance
- Lenses are typically worn overnight while sleeping (e.g. 6–8 hours). (FDA Access Data)
- Upon waking, lenses are removed, and patients often enjoy clear vision during the day without glasses or contacts—though peripheral vision or sharpness may slowly regress, so some wear at midday may be needed. (U.S. Food and Drug Administration)
- To maintain the effect, regular (often nightly) use is required. If usage lapses, corneal shape reverts and refractive error returns. (U.S. Food and Drug Administration)
- Rigorous lens cleaning, disinfection, and follow-up care are essential to reduce infection risk. (Lippincott Journals)
Who Is a Good Candidate?
- Patients with myopia within moderate range, ideally ≤ –6.00 D and limited astigmatism, without corneal pathology. (FDA Access Data)
- Patients motivated for strict hygiene and follow-up compliance.
- Younger patients may benefit especially for myopia control.
- Not ideal for those with very dry eyes, irregular corneas (e.g. keratoconus), or poor compliance.
Bibliography
Liu, Y. M., et al. “The Safety of Orthokeratology—A Systematic Review.” CLAO Journal, vol. 42, no. 1, 2016.
Sartor, L., et al. “Benefits and risks of orthokeratology treatment.” PMC (National Institutes of Health).
Hiraoka, T., et al. “Myopia Control With Orthokeratology: A Review.” PubMed / NCBI.
Li, X., et al. “Orthokeratology in controlling myopia of children: a meta-analysis.” BMC Ophthalmology.
Wang, A., et al. “Influence of orthokeratology lens treatment zone decentration on myopia control.” PM (Amegroups).
Paragon Vision Sciences. “Paragon Z CRT Package Insert.” FDA PMA documents.
U.S. Food & Drug Administration. “Types of Contact Lenses – FDA.”
