Accelerated Orthokeratology


What is AOK?

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 to wear and very easy to care for.

By slight modifications in the shape of the cornea, clear functional vision is achieved throughout waking hours. This is achieved by gently flattening the the top layer of the cornea - the epithelium. The amount of flattening required is approximately 6 microns per 1 dioptre of myopia. Thus to eliminate myopia of 4 dioptres the corneal epithelium needs to be flattened by approx 24 microns - only 0.024 millimeters.

Reverse Geometry Lenses

AOK uses specially designed 'reverse geometry' RGP contact lenses to gently reshape the cornea overnight while sleeping. Reverse geometry means that the contact lens fits closer to the eye centrally, and further away from the cornea peripherally. This creates a fluid pressure gradient that gently flattens the epithelium - and this is the change required to reduce myopia. The picture to the right is of a well-fit AOK or Ortho-K lens using fluorescent dye in the tearfilm to demonstrate the reverse geometry pattern.

After the retainer is removed, the cornea retains its new shape throughout the following day, thus providing clear vision. The retainers need to be worn nightly to maintain the effect. Once the correct corneal shape is well-established (after several years of wearing the retainers nightly), many AOK patients can reduce their wearing schedule to every other night or approximately 3 nights a week.

The History of Orthokeratology (Ortho-K & AOK)

Ortho-K started more than 50 years ago when eye doctors noticed that some of their patients wearing RGP contact lenses had unexpected decreases in their myopia even when out of their 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's highly advanced technology with oxygen permeable polymers, computer-assisted lathes, and incredible digital corneal measuring and mapping, it is possible to achieve reduction of myopia in a matter of days. Wearing time for retainer lenses can be as little as two nights per week and retainers are only ever worn during sleep, leaving your eyes free of glasses or contacts during waking hours. This is why modern Ortho-K is commonly called Accelerated Orthokeratology or 'AOK'. It has also become know by various branded names including 'VST' (Vision Shaping Therapy), and 'CRT' (Corneal Refracted Therapy), by contact lens companies that offer their version of the lenses used.

The Benefits of AOK

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 without dependence on glasses or contact lenses in cases of emergencies.

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.

More on the AOK Process

Our AOK doctors will measure the curvature of your cornea using the corneal topographer. It is like having your picture taken and is painless, taking about five minutes. Specialized software programs are used to determine appropriate diagnostic or 'test' retainers to be worn by the patient for an overnight trial. Our staff will teach you how to insert and remove the retainers and you will wear them 1 or 2 nights and then we will have you back in the clinic to measure the improvement in vision and to check your corneal health. If all goes as expected the trial will be a success and we can proceed with full AOK treatment in custom designed retainers. Occasionally the test retainers may not give the expected results if they are either too flat or too steep; in this case we would use the results to calculate another set of diagnostic retainers and repeat the trial process.

Once we have achieved a successful trial we can proceed to order custom retainers designed specifically for your eyes to give the best results possible. The results will be apparent immediately - most patients are able to do without their glasses after a week of wearing the custom retainers. During the first few days or weeks your vision may fade slightly towards the end of the day, but over time you will achieve the ability to maintain clear vision from morning until bedtime.

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. 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.

Who is a Candidate for AOK? Who is not a Candidate?

Our AOK patients range from 8 years old to people in their 60's. Only low to moderate amounts of myopia (nearsightedness) or astigmatism can be treated. Myopia greater than -4.50 dioptres and astigmatism greater than -1.00 can be difficult to treat and we generally do not accept cases significantly above these limits.

For the cases of young teens with rapidly increasing myopia, we may proceed with AOK even if the prescription is higher than -4.50 simply to reduce the level of myopia as much as possible and also to reduce the amount of any further increases in myopia over time. For example if we can reduce the myopia from -5.50 to say -1.50 in a child or teenager, they will only require a light eyeglass prescription to use part time for distance vision - such as seeing the front of the classroom for kids or for driving in the case of young adults.

Currently, we do not treat hyperopia (farsightedness) with AOK - although there have been current developments in this area as well as for the treatment of high astigmatism and we hope to offer suitable treatments for these conditions in the future.

Patients with any of the following conditions are not suitable for AOK treatment:

AOK in the News

Dr. Mowbray discusses that may be exacerbated by the wearing of any contact lenses.

Connect with Us!