Orthokeratology is the name of a procedure used to correct myopia (short-sightedness) using contact lenses. It is temporary and relatively painless. The procedure has its roots in a traditional Chinese technique for correcting myopia, in which the sufferer would sleep with small bags of sand on their eyes. As myopia is caused by a lengthening of the eyeball, the weight of the sandbags would temporarily flatten the eye, restoring normal vision for a time.
This is the principle on which orthokeratology operates. Instead of using sandbags, contact lenses are worn on the eyes during sleep1. Overnight, the contact lens places pressure on the layer of tears covering the cornea2, and thus myopia is reduced.
The lens itself is of the rigid gas-permeable type. These are relatively hard, making them uncomfortable for daily wear, but allow pressure to be applied. Oxygen can penetrate the lens membrane, preventing eye infections. Lenses are changed yearly, but can last longer if cared for properly. They can also fracture during cleaning or if handled carelessly, rendering them useless - even hazardous.
Vision correction is initially minor, although results improve with regular wear. A good result is the restoration of near-perfect vision, lasting for a period of greater than 20 hours.
Orthokeratology can become expensive and, unlike laser surgery, it is not permanent. It does, however, avoid the drawbacks of glasses. Use of orthokeratology can be discontinued at any time and vision will slowly return to pre-treatment levels. It is a reliable method of vision correction that allows one to carry out many activities that glasses prohibit, such as swimming and contact sports, but without the expense or danger of laser surgery.
More information on the procedure, and the subtle difference between types of orthokeratology, can be found at AllAboutVision.com.