Accelerated Orthokeratology (AOK) is a non-surgical procedure which can reduce or eliminate myopia (nearsightedness) in both adults and children using specially designed 'retainer' contact lenses. The principle of AOK is similar to the use of a dental retainer used by an orthodontist to realign teeth. The retainer contact lenses are worn at night while sleeping. They are removed upon awakening to provide clear vision without using eyeglasses or contact lenses! The retainers are comfortable and very easy to care for.

Nearsighted Eye (cornea is too steep)	AOK Lens in position over cornea	Reshaped cornea after retainer wear

Specifically, AOK uses 'reverse geometry' contact lenses to gently reshape the corneal epithelium. After the contact lens is removed, the cornea retains its new shape for all or part of the remainder of the day. A retainer lens must be used each night to maintain the corneal flattening, or the myopia will revert to the pre-treatment level. Once the correct shape and a regular wearing schedule are established, many AOK patients can reduce their wearing schedule to every other night or even just 2 nights a week.

Yesterday
The procedure was first used over 40 years ago when eye doctors noticed that some contact lens wearers' vision improved after wearing their hard lenses. Initially, only old-fashioned, hard contact lens material (PMMA) was used, which was not suitable to overnight wear. A series of lenses were needed, each lens flattening the cornea a small amount until the desired results were attained. This took months to years to accomplish, and lenses often needed to be worn during the day as well.

Today
Now, with the advent of space-age oxygen permeable polymers, computer-assisted lathes, and technological advancement in corneal measuring and mapping, it is possible to achieve reduction of myopia in a matter of hours. This is why modern Ortho-K is commonly called Accelerated Orthokeratology (AOK). Wearing time for retainer lenses can be as little as one or two nights per week. That's right - retainers are worn only during sleep, leaving your eyes free of glasses or contact lenses during waking hours.

Children as well as adults can be treated with AOK because the principle of flattening the cornea is effective for both. For children, whose myopia is unstable and often increases throughout their teen and preteen years, refractive surgery is not an option. AOK, however, does not require refractive stability, and the therapy can be started in children as young as 8 years of age.

The Cornea

The cornea makes up about two-thirds of the eye's total power to focus light precisely on the retina (receiving screen), which is located in the back of the eye. By slight modifications in the shape of the cornea, clear functional vision may be restored for a period of time. This improvement is temporary, therefore retainer lens wear must be continued on a prescribed wearing schedule to maintain the therapeutic effect of the myopia reduction. This flattening is accomplished by shifting the outer layer of the central cornea - the epithelium - more peripherally, thus flattening it. The amount of flattening or shift is approximately 6 microns per dioptre of myopia. A micron is one millionth of a meter, or one thousandth of a millimeter.

Corneal Topography - Videokeratography
AOK utilizes precise instrumentation to accurately determine the corneal shape before treatment.

Corneal maps or 'topographies' are taken to determine if the corneal shape is changing in the correct manner to achieve the desired effect. The typical post-treatment map shows a central red ring (a steepened area) surrounding the flattened area which appears blue. The flat area must be centered over the pupil to provide maximum benefit.

In this example (see photo), the pre-treatment map is shown in the top left, the post-treatment map is shown in the bottom left, and the larger map on the right shows the overall change.

Benefits
AOK is not only an excellent alternative to the wearing of spectacles, but it also frees the individual from the distractions caused by perspiration, dust, wind weather and temperature. There are no more blind spots caused by frame or lens edges. It is great to wear "regular" fashion sunglasses, to get up at night or in the morning and see, to go swimming and skiing, to drive in a convertible with the top down, to work in the dust, grass or in the garden, and to be able to see in cases of emergencies.

People in occupations that are hindered by the use of glasses or contacts may be good candidates for AOK - pilots, policemen, firemen, etc. - infact we have performed AOK for patients in each of these occupations.

The Process

There are several AOK procedures, mostly associated with different lens designs. We use a procedure associated with the BE AOK lens which was developed in Australia. It has proved to be highly reliable and predictive, with consistently excellent outcomes from both the doctors' and patients' perspective. Our AOK specialist measures the curvature of your cornea using the corneal topographer. It is like having your picture taken and is painless, taking about five minutes. Our doctors also use software to help design the lenses. Diagnostic lenses will be placed on your eyes for an overnight trial. This validates the measurements of your eyes and helps to determine the proper lens.

BE retainer lenses use a 'reverse geometry' design. This means that the central portion of the contact lens fits closer to the eye than a standard contact lens - creating a fluid pressure gradient - though it doesn't touch the cornea as there is a tear layer protecting the eye. The reverse geometry part of the lens surrounds the central visual zone and is further away from the cornea than standard lenses causing a negative fluid pressure zone. The pressure gradient thus created gently redistributes the epithelium.

If we prescribe overnight AOK, expect results immediately. Your vision should be markedly improved after the first night. During the first few days or weeks your vision may fade slightly later in the day. Improvement should be noticed each day. After several months of treatment, we can sometimes reduce the wear schedule for the retainer lens from nightly to every other night or even less. Generally only one pair of lenses is needed for the BE AOK therapy but additional lenses may be required to achieve desired results. Because AOK is reversible, your vision will regress to pre-treatment levels if you stop wearing your lenses. AOK is also adjustable. Should your prescription change, your AOK lenses can be redesigned to provide more or less correction. This is one of the most significant advantages of Accelerated Orthokeratology. Adjustable, reversible, and predictable outcomes without surgery!

Why Haven't I Heard About AOK?
The practice of AOK requires a great deal of technical skill, specialized equipment and considerably more office time and is therefore costly. Many practitioners are not willing to invest the time, effort, and money required to become qualified and proficient at AOK. If a doctor is not trained in AOK, they may not suggest this as an option. It is simpler for them to offer contact lenses, glasses, or refractive surgery.

Who Is Not a Candidate? People with any of the following conditions should not undergo AOK treatment: Any eye disease, injury or abnormality that affects the cornea, conjunctiva or eyelid Severe insufficiency of tears - dry eyes. Any systemic disease that may affect the eye or be exacerbated by wearing contact lenses. Eye allergies which may be induced or exaggerated by wearing contact lenses or use of contact lens solutions.

Is AOK in your future?
Only you and an eye doctor specifically trained and certified to provide AOK can decide that. To find out if you are a candidate for Accelerated Orthokeratology, contact our office and book an appointment with one of our certified Orthokeratologists.

AOK in the News
Dr Mowbray discusses AOK on City TV with Health Correspondent Cindy Leong