What Is Orthokeratology?
Orthokeratology, or Ortho-k, involves the use of specially designed rigid gas permeable (RGP) contact lenses to alter the shape of the cornea in order to reduce or correct short-sight (myopia). It can also be effective with low degrees of certain types of astigmatism (when the front of the eye is rugby ball shaped).
In the last ten years technology has become available to accurately scan the cornea and manufacture lenses that will achieve a controlled and precise reduction in the eye’s optical imperfection. In addition new developments in lens materials have been made that enable safe overnight wear to be possible.
The technique of Ortho-k is now a safe, viable and reversible alternative to laser refractive surgery.
The cornea is mouldable and returns to its original shape if lens wear is stopped. For this reason, lenses are always worn nightly, alternate nights or 4-5 hours each day after the ideal corneal shape has been achieved in order to retain the effect.
Why Have Ortho-k Done?
The main purpose of Ortho-k is to be free of both contact lenses and spectacles for the majority, or more typically, all waking hours. The freedom from any artificial aid appeals to short-sighted (myopic) spectacle and contact lens wearers and is ideal for sportsmen, those who work in dusty or dirty environments or people who find spectacles or conventional contact lenses inconvenient. In addition, those who need to have a certain degree of uncorrected vision to satisfy their employers or a licensing body (e.g. pilots, police) can also be helped by Orthok. Most patients wear the lenses overnight and remove them on awakening.
Possibly one of the ideal situations for using Ortho-k is for the child or teenager with early myopia. Apart from the advantages already given above, there has been some strong suggestion that the procedure appears to retard the progression of the myopia (this has not yet been scientifically proven).
Who Is Suitable For Ortho-K?
The procedure works best up to a maximum spherical prescription of -5.00D. Astigmatism up to a -1.00D vertical cyls and up to -2.50D horizontal cyls.
Shortsightedness above this may be reduced but total correction is not usually possible but still very acceptable.
Also, there are several unknown factors for each individual; the complexity of the corneal shape and the response of the cornea itself.
Thus the speed of corneal moulding from one individual to the next will vary. Whilst the success rate is very high, total success cannot be guaranteed due to these factors.
What Does The Initial Visit Involve?
The initial assessment appointment includes a full eye examination and computerized corneal topographical scanning which provides a computer generated contour map from 80,000 analysed points This gives the practitioner a chance to assess both the general condition and health of the eyes and also to determine the likely effect of the procedure in that individual .These corneal scanning maps can then be used to make a pair of custom fitted lenses.
Ortho-k contact lenses, made from highly oxygen permeable rigid material, are then fitted to gently reshape the cornea towards less curvature and a more spherical shape. These will be worn for an initial trial and the response evaluated. This will typically take place overnight with a review the next morning. The effect should be a reduction of the myopia and astigmatism with improvement in the unaided eyesight. The corneal health will be carefully evaluated to ensure that it is not compromised. Only when the patient demonstrates an excellent response to the orthokeratology trial will the treatment commence.
What Does The Treatment Involve?
Once a patient has shown the appropriate response to a trial, they will start to wear lenses on a regular basis, typically overnight. For the first two to four weeks the vision may not be sufficiently good for all day-to-day activities. In these circumstances daily disposable soft lenses will be worn. After the first month, excellent vision and comfort are normally maintained whilst wearing Ortho-k lenses. Occasionally more than one set of lenses are required to effect the desired change.
As most of the visual changes occur rapidly in the first few weeks, fairly frequent examinations and possible lens changes need to take place then. Stabilisation procedures then follow at a slower pace over the next few weeks. The programme length varies between 1 and two months depending upon the degree of visual error. All orthokeratology patients are required to sign up to a monthly direct debit scheme, as payment for their future appointments and products required.
The final wearing time depends on many variables, but the treatment aim is good unaided vision all or most waking hours, with lenses being worn overnight or part of each day only. Some patients will be able to wear their lenses every second night.
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