Orthokeratology, sometimes referred to as orthoK, is an optical correction mechanism that uses hard contact lenses to physically reshape the eye in order to improve vision. In overnight orthokeratology, which is the most common application of this method, the special lenses are worn only at night, and the temporary effects produce enhanced vision in the user during the subsequent day. The benefits are mainly in the correction of myopia, or short sightedness, and to some extent the correction of astigmatism.
The process is not suitable for all patients, as it relies on a certain eye structure. Some people, for example, have particularly steep or flat corneal curves, and these may not experience much benefit from the procedure. Patients for whom the method is often recommended include people who have difficulty wearing contact lenses during the day, for example because they work in an environment with a dusty atmosphere, or spend very high proportions of time working with computer screens, or partake in certain sporting activities which may make them prone to losing contact lenses.
The material from which orthokeratology contact lenses are manufactured is crucial for maintaining the health of the eye. The wearing of contact lenses may compromise the amount of oxygen available to the eye, and complications may result from oxygen deprivation, called corneal hypoxia. In extreme cases, this may result in ulcers of the cornea, bleeding, and vision impairment.
A modern orthokeratology lens is typically a rigid lens made of a special gas permeable substance that allows high levels of oxygen to permeate through the lens to the eye. Most manufacturers of orthokeratology lenses adhere to standards and technologies approved by the United States Food and Drug Administration (FDA). The material of the lenses is given a rating that relates to the level of its permeability to oxygen, known as a ‘Dk’ rating.
Accelerated orthokeratology is a term used by some providers of the treatment, and patients may indeed experience rapid results. The lenses work by gently exerting pressure on the eye to effect redistribution and reshaping of the cells of the cornea cell. Vision improvements may be experienced immediately after the first overnight wearing of the lenses, and continued improvements may follow over a period of several weeks, after which the eye will stabilize. Orthokeratology lenses must be worn on a continued basis, as if the lenses are discontinued, the eye will simply return to its original shape.