Corneal refractive therapy is a non-surgical, safe, and reversible process that reshapes the cornea, i.e., the front eye surface, using specially designed contact lenses during sleep. The technique is useful in correcting some forms of refractive errors to provide clear vision without the need for prescription lenses. However, the lenses must be worn during sleep each night because the effect is temporary.

The cornea is the eye's primary lens and is responsible for focusing close to 70 percent of the light on the retina, the light-sensitive spot at the back of the eye. Corneal abnormalities cause refractive errors by affecting the bending of light, which leads to poor vision. CRT is a non-surgical technique to correct corneal disorders.

The therapy involves the patient wearing special, therapeutic gas permeable contact lenses overnight. The ortho-k lenses are designed to gently reshape the cornea as the patient sleeps and are removed when the patient wakes up. The patient will have a clear vision throughout the day and will need to wear the therapeutic lenses every night for clear eyesight.

CRT is an ideal vision correction method for myopic children with progressive nearsightedness and people who are very active or involved in sports. The therapy is used to stop or slow nearsightedness progression in children and is an excellent option for adults with dry eyes. It's also the right choice for people whose careers and hobbies make it inconvenient for them to wear prescription lenses, i.e., eyeglasses or contact lenses. The therapy can also help boost myopic children's self-esteem because they don't have to worry about wearing glasses throughout the day. They can wear non-prescription glasses or goggles like other kids while they are playing sports.

CRT is most often used to temporarily correct mild and moderate nearsightedness and lesser amounts of farsightedness, presbyopia and astigmatism. The degree and type of refractive aberration that can be managed effectively with CRT varies on an individual basis. The doctor can give the patient more specific guidance after an eye checkup.

Also Known As

  • CRT
  • GVSS
  • Ortho-k
  • Vision shaping
  • Orthokeratology
  • Overnight vision correction
  • Overnight corneal reshaping
  • Gentle vision shaping system
  • Corneal reshaping contact lenses
  • Overnight contact lenses to correct or control myopia


Before the Procedure

The eye doctor has to fit the ortho-k lenses to reshape the patient's cornea. S/he will begin by performing a comprehensive eye examination to ensure that CRT is a suitable treatment option. It also helps the doctor to determine the best type of corneal reshaping lenses for that particular patient. Then, s/he will measure the patient's corneal curvature through a computerized mapping method known as corneal topography/tomography. It's a non-invasive and painless digital technology that provides the patient's eye surface topographical map in about a minute.


Depending on the corneal topography measurements, the doctor may fit the patient with ortho-k lenses from the in-office inventory or order custom lenses for later fitting. It's vital to note that the patient may have to use a series of temporary lenses for clear vision until they achieve the targeted prescription. Most patients usually need about three pairs of therapeutic lenses to attain the maximum sight correction effect.

Risks & Complications

CRT involves little risk because the effect is temporary, and the patient can discontinue the therapy lenses at any time.

In the initial days, the patient may be conscious of the lenses until they fall asleep. The patient may also experience blurred vision, mild glare and halos around lights, until the eyes are fully corrected. In sporadic cases, these may persist even after correction.

One of the outstanding benefits of CRT is that the patient can experience quick results. Many patients wake up to clearer vision after wearing the lenses for a night or two. It's mainly the case in patients with low prescriptions, and the effects can last a whole day. 

For patients with higher prescriptions, the process may take two weeks for maximum correction. In some cases, the patient may have to wear lesser prescription lenses during the CRT process.

FDA trials for CRT indicated that over 90 percent of the patients achieved 20/40 visual acuity. It means they met the requirements to drive without wearing prescription lenses in most states in the US.