Orthokeratology (often abbreviated to Ortho-K) is a technique in which rigid gas-permeable (RGP) contact lenses are used to mould the cornea to a flatter curvature, thus reducing myopia (short-sightedness). These lenses are worn during sleep and removed upon waking, the effect lasting from several hours in the first week to several days as therapy progresses. This has been compared to the use of braces to straighten teeth by orthodontists. The treatment is an attractive alternative to laser surgery as, unlike LASIK or PRK, it is reversible merely by discontinuing wear.

After an initial assessment for suitability, a trial of overnight wearing of standard trial lenses is conducted, with a check the next morning to assess the results. An additional overnight trial may be required. Once the correct lens parameters are established, lenses are custom made for the individual and dispensed. Patients are checked regularly for lens effectivity and eye health. Many wearers are able to sustain the desired effect by wearing the lenses only two or three times per week.

The risks of Ortho-K are basically the same as the risks involved in regular contact lens wear.

Ortho-k has been around for over 30 years, but the results were very hit & miss due to a lack of understanding of the principles involved. With the development of new contact lens materials, allowing safe overnight wear, improved accuracy of lens manufacture and sophisticated corneal mapping instrumentation as well as better understanding of the physics of corneal moulding, Ortho-K has progressed from an art to a scientific discipline with predictable and measureable results.

Ortho-k is an accepted optometric procedure and as such, attracts the same benefits. However, as Medicare does not cover contact lens consultations for patients with less than 5D of myopia, and Ortho-K treatment is mostly suitable for low myopia, many patients will be ineligible for Medicare benefits. Health funds may have a distinct Ortho-K lens rebate or may simply pay the regular RGP refund.

As Ortho-K requires specialised equipment and training, most optometrists do not offer this treatment.