also known as Ortho-K, OVC (Overnight Vision Correction) and CRT (Corneal Refractive Therapy).

Corneal Topography Plot (shape map)

Green/yellow = average curvature. Blue = flat. Red = steep.

The original corneal shape is top left, mainly green. The final corneal shape is bottom left, now almost entirely blue. The so-called subtractive plot (right) represents the difference between the two. The annular pattern indicates that the cornea has been changed by ortho-keratology in a regular manner without introducing unwanted distortion.

What Is Ortho-K?

Orthokeratology (Ortho-K, or OVC – overnight vision correction) is the use of Contact Lenses to mould the shape of the cornea to eliminate or reduce Myopia (short-sight) and moderate degrees of astigmatism. It is rather like using contact lenses to achieve the same results as modern laser surgery for correcting short-sight and in some ways is similar to the use of dental braces by an orthodontist to realign teeth.

The main difference is that Ortho-K does not give a permanent change. The cornea is highly elastic and will return to its original shape. For this reason Retainer Lenses are necessary to maintain the improvement in vision. They are worn either overnight or for 2-3 hours during the day after the ideal corneal shape has been reached.

Why Have Ortho-K Done?

The main purpose of Ortho-K is to be free of both contact lenses and spectacles for the majority of, and possibly all, waking hours. The freedom from any artificial visual aid appeals to most short-sighted patients and is ideal for sporting and social activities as well as for those who work in dusty environments or other conditions difficult for contact lenses.

Is Everyone Suitable for Ortho-K? – No!

The procedure works best for low to medium short-sight – up to about 3.00D of myopia and moderate degrees of astigmatism (-1.00D). Prescriptions greater than this may well be reduced but total correction is not usually possible. In addition, the procedure may not work as effectively on very steep or very flat eyes. There are also several unknown factors for each individual patient, such as the complexity of the corneal shape and the rigidity of the cornea itself. The speed of corneal moulding therefore varies considerably from one patient to another. Whilst results in general prove very good, success can never be guaranteed due to several ocular factors outside of the contact lens practitioner’s control.

The ideal patient for Ortho-K is usually the teenager who is just becoming short-sighted. The technique not only has all of the above advantages but also appears to have some effect at stabilising or even retarding any future increase in myopia.

For older patients and those with higher prescriptions, there is sometimes a sufficient improvement in vision when lenses are removed to make Ortho-K worthwhile.

What Does The Procedure Involve?

The first step, before commencing Ortho-K, is an initial appointment to include a full ocular examination to assess the general condition and health of the eyes followed by a detailed assessment of the corneal shape. The technique uses new computerised scanning instrumentation to produces a topographical colour map of the cornea. It is then possible to discuss the likelihood of your success with Ortho-K contact lenses.

These specially designed hard lenses are made from modern materials with extremely high oxygen permeability. With recent lens designs a single pair will often produce the desired effect but sometimes it is necessary to fit a series of lenses in progressive stages gently to reshape the cornea to a shallower and more spherical curvature. As the myopia and astigmatism reduce, the unaided vision dramatically improves. The Ortho-K lenses are calculated to give good vision while worn and their sophisticated design generally makes them quite comfortable.

Most of the improvement in vision occurs rapidly over the first week or two, requiring frequent examinations to monitor progressive changes in the corneal shape. New lenses are ordered and supplied as necessary. Stabilisation then follows at a slower pace over the next few weeks. The length of the Ortho-K programme varies between 3 and 6 months depending upon the degree of short-sight and rate of response of the cornea.

Overnight wear

Ortho-K lenses were originally worn during the day, but recent experience has shown that overnight use gives several advantages. There is no discomfort from dust, foreign bodies or dry eyes; lenses are less likely to be lost or damaged; and gradually the waking day becomes increasingly free of both contact lenses and spectacles. Overnight use is not the same as ‘continuous wear’ because the Ortho-K lenses are removed during the day.

Retainer Lenses

When the optimum result has been achieved, the final pair of ‘retainer lenses’ is worn to stabilise the new corneal shape. The wearing time depends on several factors but the treatment aims to give good unaided vision for all or most waking hours. The Retainer Lenses are also worn either overnight or for just a small part of the day. Some patients need to wear their final lenses only every second or third night.

Most Ortho-K patients have a spare pair of lenses so that in the event of loss or damage the wearing schedule is not interrupted.

Because of wear and tear with use, it is advisable to replace lenses at least once a year.

What Are The Advantages of Ortho-K?

  • Good vision without spectacles or contact lenses for most of the day.
  • It is not a surgical procedure.
  • It is reversible.
  • It is not painful.
  • The technique uses well established contact lens procedures with minimal risk of problems.

Compared with Laser Surgery, Ortho-K:

  • Treats both eyes at the same time.
  • Is less expensive.
  • Does not involve post-operative pain.
  • Does not leave hazy vision.

What Are The Disadvantages of Ortho-K?

  • Several visits are required over the first few months.
  • It is essential to wear Retainer Lenses or the cornea will revert to its original shape.
  • The precise reduction of myopia cannot be guaranteed as it varies from one person to another.
  • For the best results, instructions must be followed exactly.


The procedure is always time consuming and may involve several lens changes. Fees for the first year are approximately £700 plus two lenses at £135 each. This is initially more than, for example, daily Disposable soft lenses but once the procedure is complete the future costs will be much less.