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Orthokeratology is the clinical term used to describe corneal refractive therapy. It describes the insertion of specialized gas permeable contact lenses for temporary correction of myopia. Wearing these reverse geometry gas permeable lenses is an alternative to wearing prescription glasses or having eye surgery. It works on most cases but not on people who are severely nearsighted.
Orthokeratology is also called OK, ortho-k, corneal reshaping and rigid contacts. It is also sometimes called overnight orthokeratology as it is a therapy that works while you sleep. It has been established as an alternative to surgery for two decades.
The history of orthokeratology begins with the Chinese practice of putting small weights or sandbags on eyelids during sleep to change the shape of the eyeball and then reduce myopia. The basic principle behind the modern practice of othrokeratology is similar only instead of weights; pressure from the gas permeable contact lenses changes the shape of the cornea instead.
The concept of flat fitting lenses that covered the entire eyeball were invented in 1888 by French ophthalmologist Eugene Kalt. These were invented to reduce myopia in people who had keratoconus.
Contemporary orthokeratology was developed in 1962, when George Jessen, accidentally discovered that ill-fitting lenses could shape the cornea. He was working with polymethylmethacrylate (PMMA) lenses at the time. Through out the sixties and seventies further research was done with regards to using flat fitting lenses to adjust eyesight.
In 1971, standards regarding this practice were defined. The International Orthokeratology Section of the National Eye Research Foundation. Technically orthokeratology is defined as “the elimination, reduction or modification, of refractive difficulties by the programmed application of contact lenses.”
These types of corrective lenses have been modified many times over the years with the main challenge for eye doctors always being how to fit stabilize them on the cornea. There are four major studies in total that have been done in this subject area. All of them reported modest successes when it comes to reduction in myopia. However results are erratic. As the effects were unpredictable orthokeratology was put on the back burner until the mid nineties.
Interest was renewed in this science when a company called Wlogyga and Stoyan invented appliances that could analyze the surface of the eye and the availability of high-Dk, gas permeable materials that made it possible for these lenses to be worn overnight.
Overnight orthokeratology is now a standard vision correction practice worldwide. In 2003, the Untied States Food and Drug Administration approved the Paragon CRT for use in overnight orthokeratology.
The Overnight Orthokeratology Regiment
In overnight orthokeratology, specialized contact lenses are inserted in the eyes at night and taken out on awakening. The effects of the corneal remolding at night ensures good vision for the rest of the day without the help of glasses or contact lenses. However the corrected vision will not persist unless the contacts are worn every single night. It only takes a week of not wearing the contact lenses to bed for the correction to reverse itself.
In modern orthokeratology, the contact lenses that are used are called reverse-geometry gas-permeable lenses. Improvement in sight is obvious after seven to ten days of wearing them. The procedure is reversible. All that you have to do is stop wearing the lenses at night to reverse the procedure.
This process works by reshaping the front corneal layers. This results in thinning of the central corneal epithelium and thickening of the surrounding mid peripheral stroma.
Results of orthokeratology
Various clinical studies on overnight orthokeratology have been conducted. The conclusion of most of them was that this is an effective corrective technique for myopia. However it is not effective on eyes that are worse than 4 diopters. Studies are being done in Asia on developing lenses that will help those with extreme myopia.
The ability of orthokeratology to correct astigmatism, hyperopia and possibly presbyopia is still being researched as are the reverse geometry contact lenses that are an essential part of the procedures.
Benefits and disadvantages of overnight orthokeratology
The benefits of orthokeratology are convenience and its non-invasive character. Many people like the idea that they can reverse their vision if they choose to wear glasses again.
Another perk is that when the lenses are removed, leftover fluids and tear film are also removed which can cause discomfort. Yet another problem is ocular dryness that makes wearing them at night uncomfortable.
Of course the main drawback of using these types of contact lenses is that the therapy is temporary. If the night use of the lenses is stopped then the cornea reverts back to its original shape. A very serious side effect is overnight hypoxia. This is a severe infection of the cornea, which can be the result of severe infections. Usually children under fifteen-year s of age get this. In severe cases, an individual may have to have a keratoplasty to bring back eyesight if the use of these reverse geometry lenses backfires.