Orthokeratology

What is the objective of the ortho-K procedure?
How is the ortho-K process performed?

Orthokeratology (ortho-K) is a nonsurgical system of treating myopia(nearsightedness) and astigmatism with a sequential series of specialized contact lenses that gradually flatten the cornea. The procedure uses rigid gas permeable contact lenses with very high oxygen permeability to gradually change the curvature of the front surface of the eye. These lenses are worn for a specific period of time then changed for new lenses with a slightly different shape. This repetitious method of fitting and changing the curves allows the anatomical shape of the cornea to slowly change, reducing the dependence on contact lenses or eyeglasses. Orthokeratology produces no permanent change in the structure of the cornea.

Although the procedure has been in existence for many years, recent improvement in lens technology and the availability of the corneal topographer, used for mapping the surface of the eye, have made the process more precise and dependable. The procedure works best for up to four diopters of myopia and two diopters of astigmatism. Refractive errors above this level may be reduced but not totally corrected.

What is the objective of the ortho-K procedure?

To understand how orthokeratology works, it is first necessary to understand the visual function of the eye. The eye works like a camera with two lenses. The first lens is the cornea, a clear membrane that covers the front of the eye. The second lens is the eye's natural crystalline lens, which is located behind the pupil. The cornea is responsible for about 70 percent of the eye's focusing power, while the natural lens fine-tunes the image before it is focused on the retina at the back of the eye. The retina works like the film in a camera, receiving light images and sending them through the optic nerve to the brain (See Anatomy of the Eye). If both lenses are working properly, the image is focused precisely on the surface of the retina and the result is perfect 20/20 vision.

Just as people are born with different sizes and shapes of hands, their eyes also vary in form and proportion. A perfect eye has an evenly rounded cornea that allows light to fall exactly on the retina, resulting in perfect vision. If the cornea is too steep or if the eye is too long from front to back, light rays are focused in front of the retina, resulting in myopia. If the front of the cornea is unevenly curved, it causes the light rays to fall on different spots on the retina, resulting in astigmatism.

The objective of ortho-K is to correct nearsightedness and/or astigmatism by reshaping the cornea in order to correct for imperfections.

How is the ortho-K process performed?

Ortho-K contact lenses, called corneal molds, are fitted in progressive stages to gradually reshape the cornea towards less curvature and a more spherical shape. Similar to a contact lens, the mold works as you wear it, whether awake or asleep. The program length usually varies between 3 and 6 months, depending on the degree of visual error and the rates of change. Over this period of time, you gradually decrease the time you wear the mold to establish the minimum wear time to maintain the corneal shape and good functional vision.

During the first phase of the program, lasting several days to several weeks, the visual changes occur quite rapidly, requiring frequent examinations and progressive lens changes. The second phase of the process, called the holding phase, lasts from 3 to 6 months and is designed to train the corneal tissue to retain its shape over a 24-hour period. In the final phase, lenses called retainer lenses are prescribed to stabilize the new corneal shape. The schedule for wear of these lenses is determined on an individual basis, but usually begins with full-time and then is reduced to short periods of the day or overnight. Your cornea will return to its original shape if you don't wear the retainer on an ongoing basis.

Orthokeratology is a controversial procedure, according to some eye doctors.