Ortho-K: A promising alternative to LASIK

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Orthokeratology (Ortho-k for short) is the use of rigid, highly oxygen-permeable contact lenses to gently and temporarily adjust the shape of the cornea to provide better, crisper vision.

Myopia, or “nearsightedness,” has always been a disadvantage for people. Whether it is eyeglasses or contact lenses, it is such a nuisance trying to have corrected vision each day. Forgetting to bring glasses when going to school, worrying about losing a contact lens when playing soccer, it’s such a hassle! It’s unclear what the actual cause of myopia is, but it seems that genetics plays an important role. We can’t really prevent ourselves from getting glasses; you either need them or you don’t. Although some adults choose to have laser eye surgery (LASIK), the results are mixed and usually entail a whole list of side effects depending on the individual. And of course, LASIK is not suitable for children and teens.

But what if we can do something that is not permanent to the eye but temporarily restores one’s vision so that regular corrective lenses would not be needed? Thanks to years of research, advances in technology and materials engineering, and a number of NASA Space Shuttle missions, this is now possible using orthokeratology.

Orthokeratology (Ortho-k for short) is the use of rigid, highly oxygen-permeable contact lenses to gently and temporarily adjust the shape of the cornea to provide better, crisper vision. In other words, one would wear these lenses for a period of time, take them off, and enjoy clear vision without the aid of additional glasses or contact lenses. These lenses look like any other ordinary contact lenses, except that they are hard and smaller. The rigid structure of the lenses provides a means for adjusting the cornea’s surface curvature, which is the ultimate goal of the treatment. Ortho-k lenses have an even higher degree of oxygen-permeability compared to regular contact lenses, which allow the eyes to breathe during treatment to maintain good eye health and avoid hypoxia during sleep, when treatment takes place.

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How regular glasses and contact lenses correct myopia
In a regular eyeball, light rays pass through a layer of clear tissue, called the cornea, which refracts them. The refracted light rays enter the pupil and then go through further refraction as they pass through the lens of the eye. The light rays finally converge on a screen called the retina at the back of the eye, forming a clear image. However, if a person is nearsighted, his or her eyeball is longer than normal. Thus, the refracted light rays entering the eye would converge sooner, before reaching the retina, diverge again, and form a fuzzy image. Glasses and contact lenses are used to make the lay rays initially more divergent so that they would converge later, right at the retina to form a clear image.

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How ortho-k lenses correct myopia
The mechanism of ortho-k is phenomenal. It takes advantage of the flexibility of the cornea, which is responsible for two-thirds of the focusing power of the eye. Thus, the cornea has the greatest influence on the behaviour of the light entering the pupil. Manipulating the shape of its surface can significantly change a person’s vision: this is the key principle of orthokeratology. The hard lenses, when worn, cause the growth of the outer corneal layer (the epithelium) to adjust. These lenses are smaller than regular contact lenses and provide a better fit for reshaping. An ortho-k lens sits on top of the tear layer which protects the cornea and the rest of the eye, not exactly touching the cornea. The ability of the lens to change the thickness of the cornea just by some micrometres significantly changes the corneal focal power.  The lens “flattens” the cornea due to the pressure on the tear layer, allowing the length of the eyeball to shorten accordingly so that light rays converge precisely at the retina to form a clear image. Ortho-k lenses correct mild to moderate myopia (-5.00 to -6.00 diopters) along with mild astigmatism (-1.5 to -1.75 diopters). However, optometrists will decide whether or not ortho-k lenses are right for certain individuals. Treatment usually takes 1 to 2 weeks to achieve full effects, with constant vision improvements after each night of use.

Advantages in night-time wear
In 2002, the US Food and Drug Administration approved the overnight wear of ortho-k lenses from Paragon Vision Sciences called Corneal Refractive Therapy (CRT) lenses. Night-time wear of these lenses has many advantages, one of which is comfort: Since ortho-k lenses are hard, they are often uncomfortable when worn during the day and especially when blinking. Blinking slightly shifts the lens, causing discomfort and irritation. Also, many people get the feeling of “a weird piece of plastic on the eye.” These issues can be avoided during sleep, when one is not conscious to notice the lenses. Reshaping takes place during sleep without irritation, providing clear vision during the day and the comfort of the lenses off.

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Ortho-K: not really a new discovery…
While orthokeratology is still unknown to many people today, it is certainly not a new idea. In fact, the concept has been around since the 1960s. However, it wasn’t until the 1990s that technological advances made it possible to treat patients with this concept. Such advances made corneal mapping possible using corneal topography. Corneal topography is a way of analyzing the surface curvature of the cornea. Similar to a regular topographical map, which maps the hills, ridges and valleys of the Earth, a corneal topographic map shows the highs and lows of the surface of the cornea. This allows optometrists to plan treatment and fitting of ortho-k lenses for patients and to monitor treatment progress. Corneal topography is also used to plan and prepare patients for laser eye surgery.

Benefits & Risks
Ortho-K lenses certainly appeal to kids and teens simply because of the hassle-free great vision that could be obtained without surgery. It is a great advantage not having to worry about broken glasses or dropped contact lenses in the middle of sports practice, dancing, or other daily activities. Other people may find these lenses useful because they work in dusty environments and are susceptible to dry eyes and/or irritation. Unlike LASIK, the results from orthokeratology are temporary, which means that a patient must continue to wear the lenses in order to maintain good vision. Once you discontinue their use, the treated corneas will slowly revert back to their original curvatures thus restoring your vision to the state before the start of treatment.

Due to its temporary, safer, and non-surgical nature, a number of people prefer ortho-k over LASIK, which is permanent and associated with many risks. However, ortho-k does pose some risks too, as some optometrists refuse to treat patients with it due to its relative complexity and unfamiliarity to the public compared to more widely-known treatments such as LASIK, regular day-time contact lenses and conventional glasses. Some risks associated with ortho-k include corneal infections and higher chances of hypoxia, risks that are also associated with regular contacts. There has also been some controversy involving eye health during sleep: that eyes should rest at night, free from any foreign objects restraining them, and that ortho-k lenses prevent eyes from breathing and resting naturally at night. Despite all these claims, many patients experience great success, achieving near-perfect to perfect vision with no side effects or complications along with great eye health. In addition, ortho-k seems to work better on children because their corneas of softer and more flexible and respond better to treatment. Current trends show that ortho-k controls myopia in children, since many children who start treatment before or during their preteen years experience little to no myopic increases by the time they reach adulthood. Hopefully, this trend would open up to more research on myopia control and prevention in the future.

Further Reading:
- http://ortho-k.net/
- http://www.allaboutvision.com/contacts/orthok.htm
- http://www.crtvision.com/