Radial keratotomy (RK) is a type of eye surgery used to correct myopia (nearsightedness). It works by changing the shape of the cornea-the transparent part of the eye that covers the iris and the pupil.
About 25-30% of all people in the world are nearsighted and need eyeglasses or contact lenses for distance vision to be clear. For a number of reasons, some people don't like wearing corrective lenses. Some feel unattractive in eyeglasses. Others worry about not being able to see without their glasses in an emergency, such as a house fire or a burglary. Both glasses and contact lenses can be scratched, broken, or lost. In addition, contact lenses require special care and can irritate the eyes.
Radial keratotomy was introduced in North America in 1978. Since then doctors have improved the technique, and its results have become more predictable. Radial keratotomy is one of several surgical techniques to correct nearsightedness, reducing or eliminating the need for corrective lenses. It is most successful in patients with a low to moderate amount of nearsightedness-people whose eyes require up to -5.00 diopters of correction. A diopter (D) is a unit of measure of focusing power. Minus lenses correct nearsightedness.
Not every nearsighted person is a good candidate for radial keratotomy. This type of surgery cannot help people whose nearsightedness is caused by keratoconus, a rare condition in which the cornea is cone shaped. The procedure usually is not done on patients under 18, because their eyes are still growing and changing shape. It is important that visual status is stable. Women who are pregnant, have just given birth, or are breast-feeding should not have the surgery because hormonal changes may cause temporary changes in the cornea. In addition, anyone with glaucoma or with any disease that interferes with healing (e.g., rheumatoid arthritis, lupus erythematosus, or uncontrolled diabetes) should not have RK.
Radial keratotomy weakens the cornea, making it vulnerable to injuries even long after the surgery. Getting hit in the head after having RK can cause the cornea to tear and can lead to blindness. For this reason, the procedure is not recommended for people who engage in sports that could result in a blow to the head (i.e., karate or racquetball).
It is important to keep in mind that RK is a permanent procedure and that success cannot be guaranteed. An experienced eye surgeon can estimate how likely it is that the surgery will help a particular patient, but that is just an estimate. There is no way to know for sure whether the surgery will improve eyesight enough to eliminate the need for corrective lenses. Vision usually improves after RK, but it is not always perfect. Anyone who decides to have RK should be prepared to accept less-than-perfect vision after surgery, which may necessitate the continued use of glasses or contact lenses. This surgery does not eliminate the need for reading glasses. Actually, someone who didn't need reading glasses before surgery because their myopia allowed near vision to be clear may find themselves needing reading glasses. Patients must ask about this prior to surgery.
Anyone considering RK should also be aware that certain professions, including branches of the military, are not open to people who have had the procedure.
A reputable ophthalmologist will discuss the risks of the procedure and should tell anyone considering it that perfect vision can't be guaranteed. Patients should be wary of any doctor who tries too hard to "sell" them on RK.
In a person with clear vision, light passes through the cornea and the lens of the eye and focuses on a membrane lining the back of the eye called the retina. In a person with myopia, the eyeball is usually too long, so light focuses in front of the retina. Radial keratotomy reduces myopia by flattening the cornea. This reduces the focusing power of the cornea allowing light to focus further back onto the retina (or at least closer to it), forming a clearer image.
A surgeon performing RK uses a very small diamond-blade knife to makes four to eight radial incisions around the edge of the cornea. These slits are made in a pattern that resembles the spokes of wheel. As the cornea heals, its center flattens out.
Radial keratotomy is usually performed in an ophthalmologist's office. Before the surgery begins, the patient may be given medicine to help him or her relax. A local anesthetic-usually in the form of eye drops-is used to numb the eye, but the patient remains conscious during the procedure. The surgeon looks through a surgical microscope while making the slits. The treatment usually takes no more than 30 minutes.
Some ophthalmologists will perform RK on both eyes at once but others prefer to do one eye at a time. It once was thought that surgeons could use the results of the first eye to predict how the well the procedure would work on the second eye. However, a study published in 1997 found that this was not the case. The authors of the study cautioned that there might be other reasons not to operate on both eyes at once, such as increased risk of infection and other complications.
The cost for RK depends on the surgeon, but usually ranges from $1,000-$1,500 per eye. Medical insurance usually does not cover RK, because it is considered an elective procedure-one that people choose to have done.
Before beginning the procedure, the surgeon marks an area in the center of the cornea called the optical zone. This is the part of the cornea that one sees through (it is the area over the pupil). No cuts are made in this region. The surgeon also measures the cornea's thickness, to decide how deep the slits should be.
After the surgery is over, the anesthetic wears off. Some patients feel slight pain and are given eye drops and medications to relieve their discomfort. For several days after the surgery, the eye that was treated may feel scratchy and look red. This is normal. The eye may also water, burn slightly, and be sensitive to light.
As with any type of surgery, it is important to guard against infection. Patients are given eye drops to protect against infection and may be told to use them for several weeks after the surgery. Because RK weakens the cornea it is important to protect the head and eyes.
The cornea heals slowly, and full recovery can take several months (another reason not to have the surgery done on both eyes at the same time). While the cornea is healing, patients may experience these problems:
- Variations in vision. Eyesight may be better in the morning than in the evening or vice versa.
- Temporary pain.
- Increased glare.
- Starburst or halo effects. Rays or rings of light around lights at night.
- Hyperopic shift. As the cornea flattens, vision may become more farsighted (hyperopic). For this reason, the surgeon may initially undercorrect the patient. This gradual shift may occur over several years.
If RK does not completely correct a person's nearsightedness, glasses or contact lenses may be needed. In general, people who were able to wear contact lenses before the procedure can still wear them afterward. Even patients whose nearsightedness was corrected may still need glasses for reading. This is especially true for middle-aged and older patients. The lens of the eye stiffens with age, making reading glasses necessary (presbyopia ). Radial keratotomy does not correct this problem.
The surgeon who performs the RK procedure will tell the patient how often to return for follow-up visits. Often, two to four visits are needed, including one the day after surgery. It is also important to know what side effects should be reported immediately to the surgeon (e.g., pain or nausea ).
Complications from RK are rare, but they can occur. These include:
- cataract a clouding of the lens of the eye, resulting in partial or total loss of vision
- serious infection
- lasting pain
- rips along an incision, especially after being hit in the head or eye
- loss of vision
- chance of overcorrection (hyperopic shift)
The chances of complications are reduced when the surgery is done by an ophthalmologist with a lot of experience in RK. Younger patients also tend to heal faster.
Cornea— The transparent part of the eye that covers the iris and the pupil.
Diopter (D)— Unit describing the amount of focusing power of a lens.
Iris— The colored part of the eye.
Laser-assisted in situ keratomileusis (LASIK)— A type of refractive eye surgery using a laser and another instrument to change the shape of the cornea.
Local anesthetic— Used to numb an area where surgery or another procedure is to be done, without causing the patient to lose consciousness.
Myopia— Nearsightedness. People with myopia cannot see distant objects clearly.
Ophthalmologist— A physician who specializes in treating eyes.
Photorefractive keratectomy (PRK)— A type of refractive eye surgery using a laser to change the shape of the cornea.
Pupil— The part of the eye that looks like a black circle in the center of the iris. It is actually an opening through which light passes.
Retina— A membrane lining the back of the eye onto which light is focused to form images.
The desired result of radial keratotomy is a reduction in myopia. A major study by the National Eye Institute, reported in 1994, tracked the success of RK in 374 patients who had had the procedure done 10 years earlier. The study found that:
- 85% had at least 20/40 vision (the acuity considered good enough to drive without glasses)
- 70% did not need glasses or contact lenses for distance vision
- 53% had 20/20 vision without glasses
- 30% still needed glasses or contact lenses to see clearly
- 1-3% had worse vision than before they had RK
- 40% had a hyperopic shift.
As with all surgeries, RK has risks. These risks include having worse vision than before the surgery; halos; glare; and although rare, blindness. Some aftereffects, such as halos or glare may last for years. Other refractive surgeries, such as photorefractive keratectomy (PRK) and laser-assisted in situ keratomileusis (LASIK) use lasers to change the shape of the cornea and they may produce fewer side effects. It is important to speak with an experienced eye surgeon who has done many refractive surgeries to fully understand the options and risks involved before making a decision.
American Optometric Association. 243 North Lindbergh Blvd., St. Louis, MO 63141. (314) 991-4100. 〈http://www.aoanet.org〉.
American Society of Cataract & Refractive Surgery. 4000 Legato Road, Suite 850, Fairfax, VA 22033. (703) 591-2220. 〈http://www.ascrs.org〉.
"Radial Keratotomy." Gale Encyclopedia of Medicine, 3rd ed.. . Encyclopedia.com. (February 26, 2017). http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/radial-keratotomy
"Radial Keratotomy." Gale Encyclopedia of Medicine, 3rd ed.. . Retrieved February 26, 2017 from Encyclopedia.com: http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/radial-keratotomy
Radial keratotomy is a type of eye surgery that is used to correct permanently myopia (pronounced my-O-pee-ah) or nearsightedness. In this surgery, a physician typically cuts slits into the cornea (pronounced KOR-nee-ah) with a tiny diamond scalpel, changing the shape of the cornea. The diamond scalpel is rapidly being replaced by laser surgery, which is quicker, more reliable, and has fewer complications.
How the eye works
The human eye can be considered a kind of extension of the brain. As an image-gathering tool, it can also be thought of as a camera, with the brain doing the developing of the picture. In many ways, a camera is similar to an eye in that both have a lens that can be focused for different distances. The retina (pronounced REH-tih-nuh), the innermost layer of the eye, can also be thought of as the film in the camera.
If looked at sideways, the human eyeball is spherical or round and has a bulge in the middle of its front. This outermost bulge or bump in its center is called the cornea. Described as a transparent (meaning light passes through) guard of the eye, the cornea is the first thing that receives the light that bounces off an image and goes into our eye. This is how human vision actually works, as our eyes detect light that is reflected from an object. The cornea is like a transparent front window that does the initial focusing for the eye. Although it is not nourished by blood, it is kept moist by a fluid called aqueous humor (pronounced AY-kwee-us HEW-mohr).
Shape of the cornea
The shape of the cornea is very important since it slows the light entering the eye and bends it toward the center of the eye where it meets the lens. Most of the focusing is done by the cornea, with the lens doing some fine tuning of the image. In general, the more curved the cornea is, the more it focuses. Myopia or nearsightedness (meaning that a person can see things better that are near than those that are far) is caused by eyeballs that are too "long" or too steeply curved. When this happens, the light rays are focused before they ever reach the retina, so that the image is out of focus or blurred by the time it does reach it.
Words to Know
Aqueous humor: Clear liquid filling the small cavities between the cornea and the iris and between the iris and the lens of the eye.
Cornea: The outer, transparent part of the eye through which light passes to the retina.
Nearsightedness: Vision disorder caused by an eyeball that is too long or a lens that is too strong; objects up close are seen easily while those far away appear blurry.
Retina: The light-sensitive part of the eyeball that receives images and transmits visual impulses through the optic nerve to the brain.
Discovery of surgical procedure
The eye surgery called radial keratotomy is a procedure that changes the shape of the cornea (and therefore how it bends light) in order to correct its focusing errors. The surgery achieves this through microscopic radial cuts made in the cornea. The word "radial" describes the pattern of slits that "radiate" out from the center of the cornea like the spokes of a wheel. The word "keratotomy" is a compound Latin word in which "kera" means cornea and the suffix "totomy" means to cut. As long ago as 1869, a Dutch ophthalmologist (pronounced aaf-thaal-MA-low-jist) or eye doctor suggested that if the cornea could somehow be flattened by surgery, it might improve certain people's vision. He conducted a series of experiments on rabbits some years later. Although others in Norway, America, Italy, and Holland performed similar experiments around the beginning of the twentieth century, it was in Japan in the 1930s that a physician named Tsutomo Sato performed about 200 operations on people with mixed results.
Modern radial keratotomy was pioneered by Russian ophthalmologist Svyatoslav N. Fyodorov in the early 1970s. There are two different stories as to how Fyodorov came to use radial keratotomy successfully. One story tells of a boy whose eyeglasses shattered and left tiny fragments of glass embedded in his cornea. Another story tells of a pilot with similar accidental cuts in his cornea. In either (or both) cases, Fyodorov noticed that when the cuts had healed, the patient's previously poor vision had improved because the cornea had been "flattened" by the accidental cuts. Fyodorov soon began to perform cornea surgeries regularly by 1974, and by the late 1970s, his new technique had become known around the world. In 1978, Leo Bores became the first to perform a radial keratotomy in the United States and soon after began training others.
Radial keratotomy was found to improve nearsightedness because it flattened the central part of the cornea by making cuts in its sides. The length, depth, and number of cuts was usually different in each case, depending on the patient's condition, age, and the curve of the cornea. This flattening of the cornea brought the focal point of the eye closer to the retina and improved distance vision. The surgery was performed using a highly precise diamond-tipped or sapphire-tipped scalpel (blade) that is set to a particular depth. This surgery is usually quick, generally painless, and its recovery period short. However, it sometimes resulted in irregular healing or infection. Others have experienced what is called "variable vision" in the course of a day, and sometimes scarring would result in blurred vision.
New laser surgery
Although radial keratotomy is still performed and even recommended for certain cases, most eye doctors now recommend it be replaced by laser surgery. Laser vision correction, now known as LASIK surgery (for LASer In situ Keratmileusis), is the newest and usually best form of radial keratotomy. Instead of using a knife to makes slits in the cornea, the surgeon reshapes the cornea using a process called "photoablation" (pronounced foe-toe-ab-LAY-shun). This process uses an intense beam of ultraviolet laser light that is precisely controlled. With it, the surgeon stimulates the molecules in the cornea to the point where certain ones break apart and vaporize. The tissue that is disappearing is actually no more than one five hundredth the thickness of a human hair. What is remarkable about this procedure is that the tissue around and even underneath is not at all affected.
Doctors use a computer to perform laser vision correction surgery and program its software according to a number of variables since each patient is different. Today's laser vision correction has become quicker, cheaper, and safer than ever. Modern LASIK has rapidly become the procedure of choice for most surgeons who recommend it because it produces better results with less discomfort in a quicker period of time. Overall, the older, scalpel-based radial keratotomy has increasingly been replaced by the newer laser-based surgery. Radial keratotomy was an important step in the evolution of vision correction surgery.
[See also Eye ]
"Radial Keratotomy." UXL Encyclopedia of Science. . Encyclopedia.com. (February 26, 2017). http://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/radial-keratotomy
"Radial Keratotomy." UXL Encyclopedia of Science. . Retrieved February 26, 2017 from Encyclopedia.com: http://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/radial-keratotomy
Radial keratotomy is a surgery performed on the covering of the eyeball (the cornea). It is used to permanently correct near-sightedness, or myopia. In myopia, light rays entering the eye's lens are bent too much. The rays focus in front of, instead of onto, the back of the eye, or the retina. In radial keratotomy, incisions made on the cornea to refocus the light rays.
The first radial keratotomy was performed in Japan in 1955. Like most new techniques, it was considered a risky procedure. Procedures were improved in the 1990s and many patients have successfully undergone the surgery.
Interviews with hundreds of patients show that after surgery, two-thirds of them were able to stop wearing eyeglasses or contact lenses. Some patients however, still needed lenses because they did not get the proper amount of correction. If there is not enough correction, the patient continues to have myopia. Too much correction however, causes farsightedness. Further refinements are being made in the procedure to eliminate these undesirable results.
Corneal sculpting, also known as laser surgery, corrects myopia in about 30 seconds. While the procedure is being performed in other countries, it is not approved for use in the United States.
"Radial Keratotomy." Medical Discoveries. . Encyclopedia.com. (February 26, 2017). http://www.encyclopedia.com/medicine/medical-journals/radial-keratotomy
"Radial Keratotomy." Medical Discoveries. . Retrieved February 26, 2017 from Encyclopedia.com: http://www.encyclopedia.com/medicine/medical-journals/radial-keratotomy