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Radial Keratotomy

Radial Keratotomy

Definition

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.

Purpose

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.

Precautions

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.

Description

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.

Preparation

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.

Aftercare

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 ).

Risks

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.

KEY TERMS

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.

Normal results

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.

Resources

ORGANIZATIONS

American Academy of Ophthalmology. 655 Beach Street, P.O. Box 7424, San Francisco, CA 94120-7424. http://www.eyenet.org.

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.

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Radial Keratotomy

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 ]

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Radial Keratotomy

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.

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Radial Keratotomy

Radial Keratotomy

Definition

Radial keratotomy (RK) is eye surgery performed to correct myopia by changing the cornea's shape.

Purpose

RK was introduced in North America in 1978. RK is one of several surgical techniques for reducing or eliminating the need for corrective lenses. It is most successful in patients with low to moderate nearsight-edness—people whose eyes require up to −5.00 diopters of correction.

Precautions

RK cannot help patients whose nearsightedness is caused by keratoconus, a condition in which the cornea is cone shaped. The procedure usually is not performed on patients under 18 because their vision is unstable. Women who are pregnant, have just given birth, or are breast-feeding should not have RK because hormones may cause temporary corneal changes. Glaucoma patients or patients with any disease that interferes with healing should not have RK.

Radial keratotomy weakens the cornea, making it vulnerable to injuries long after surgery. A head injury after RK can cause the cornea to tear and can lead to blindness. Sports enthusiasts should be warned of this danger.

RK's success cannot be guaranteed. An ophthalmologist estimates the probability of the surgery's success in correcting vision. In some cases, patients with myopia that has caused their near vision to be clear prior to surgery may need corrective lenses for near vision following surgery. Some patients still require lenses for distance vision. RK does not eliminate presbyopia and the eventual need for reading glasses.

Description

With clear vision, light passes through the cornea and the lens of the eye and focuses on the retina. In a myopic patient, the eyeball is usually too long, so that light focuses in front of the retina. RK reduces myopia by flattening the cornea. This flattening reduces the cornea's focusing power, allowing the light to focus further back onto the retina, forming a clearer image.

For RK, a surgeon uses a small diamond-blade knife to make four to eight radial incisions approaching 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.

Before surgery the patient is given a sedative. A local anesthetic—usually eye drops—is used to numb the eye. The patient remains conscious during the procedure. The surgeon utilizes a surgical microscope to magnify the cornea while making the slits. The treatment usually lasts 30 minutes.

Most ophthalmologists perform RK on one eye at a time. Surgeons once thought they could use the results of the first eye to predict how the well the procedure would work on the second eye. However, a study in the American Journal of Ophthalmology in 1997 found that this was not the case. The authors cautioned that there might be other reasons not to operate on both eyes at once, such as increased risk of infection.

RK's costs depends on the surgeon, but usually range from $1,000 to $1,500 per eye. It is usually not covered by insurance.

Preparation

RK patients should be carefully screened by an ophthalmic assistant or physician before surgery is approved to avoid possible complications. This screening should include a comprehensive eye exam, either by the ophthalmologist or a co-managing optometrist at least a few days before surgery. At this time, the physician or ophthalmic assistant should chart any dry eye or any corneal disease that may hinder surgery. They also should perform corneal topography, which creates a map of the patient's eye.

Assistants must advise patients to discontinue wearing contact lenses weeks prior to the visual exams to make sure vision is stable; and they must also advise the doctor of contact lens wear.

Before surgery, ophthalmic staff administer eye drops and a sedative to the patient. The physician tests the patient's vision, and the patient rests while waiting for the sedative to take effect. Immediately before the surgery, ophthalmic staff administer local anesthetic eye drops.

Before beginning the procedure, the surgeon measures the cornea's thickness to decide how deep the slits should be, and marks an area in the center of the cornea called the optical zone. This is the part of the cornea in the area over the pupil that the patient sees through. No cuts are made in this region.

Aftercare

After surgery, some patients feel pain and are given eye drops and medications to relieve discomfort. For several days the eye may feel scratchy and look red. This is normal. The eye also may water, burn, and be sensitive to light.

Patients should be advised to use eye drops for several weeks to protect against infection. Patients also should be told to protect the head and eyes.

The cornea heals slowly, and full recovery can take months. This is one reason RK has fallen out of favor with surgeons and patients. Laser-refractive surgeries, such as laser-assisted in situ keratomileusis (LASIK), have better results with faster recovery. Such procedures as LASIK and corneal rings have rendered RK virtually obsolete.

While the cornea is healing, patients may experience better eyesight in the morning than in the evening (or vice versa); pain; glare; starburst or halo effects; or a hyperopic shift. As the cornea flattens, vision may become more hyperopic. For this reason, the surgeon may initially undercorrect the patient. This gradual shift may occur over several years. This procedure leaves permanent scars on the cornea.

If RK does not completely correct nearsightedness, corrective lenses may be needed. Presbyopic patients will still require reading glasses.

Patients return to the surgeon for a follow-up exam one day post-operatively. After that, patients may be referred to the co-managing optometrist for the subsequent three or four visits. Patients should be advised to report any pain or nausea immediately to the attending physician.

Complications

Complications from RK include:

  • cataract
  • infection
  • lasting pain
  • tears along an incision, especially after being hit in the head or eye
  • vision loss
  • hyperopic shift

Complications are reduced when an ophthalmologist experienced with RK performs the surgery. Younger patients also tend to heal faster.

Results

The desired result of radial keratotomy is myopia reduction. A study reported by the National Eye Institute in 1994 tracked the success of 374 patients who had RK 10 years earlier. The study found that:

  • 85% had at least 20/40 vision.
  • 70% did not need corrective 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.

Health care team roles

Allied health professionals help prepare patients for refractive surgery. Advanced and intermediate level ophthalmic technicians perform refractions and help determine the patient's eligibility for surgery. These professionals also may perform corneal topography.

Specially trained ophthalmic nurses assist during surgery. They prepare the operating room and equipment, and administer eye drops. Advanced ophthalmic technologists, who are trained for additional duties such as taking ophthalmic photographs and using ultrasound, may administer eye medications, perform tests, maintain surgical equipment and assist in refractive surgery.

Training

The American Society of Cataract and Refractive Surgery keeps physicians informed of the latest advances in surgery. Optometrists are advised to observe surgeries and attend seminars to learn more about follow-up treatments.

Ophthalmic assistants who want to assist in these surgeries can receive additional training from certified education programs.

KEY TERMS

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 microkeratone to change the shape of the cornea.

Local anesthetic— Used to numb an area in which 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.

Resources

PERIODICALS

Azar, Dimitri, M.D. and Khoury, Johnny M.D. "Understanding Wound Healing After Refractive Surgery." Review of Ophthalmology Online 〈http://www.revophth.com/RPC5F9.HTM〉.

Brown, David C., M.D. "How to Diversify." Ophthalmology Management Online〈http://www.ophmanagement.com/archive_results.asp?loc=archive/11119934028pm.html〉.

Feldman, Miriam Karmel. "Cataract Warning: RK Patients Need Special Care." EyeNet Magazine Online〈http://www.eyenet.org/eyenet_mage/02_00/cataract.html〉.

Koffler, Bruce H., M.D. "Post-Op Strategies." Ophthalmology Management Online〈http://www.ophmanagement.com/archive_results.asp?loc=archive/1180041950pm.html〉.

ORGANIZATIONS

American Academy of Ophthalmology. P.O. Box 7424, San Francisco, CA 94120-7424. (415) 561-8500. 〈http://www.eyenet.org〉.

American Optometric Association. 243 N. Lindbergh Blvd., St. Louis, MO 63141. (314) 991-4100. 〈http://www.aoanet.org/aoanet/〉.

American Society of Cataract & Refractive Surgery. 4000 Legato Road, Suite 850, Fairfax, VA 22033. (703) 591-2220. 〈http://www.ascrs.org〉.

OTHER

"Refractive Surgery: New Options in Vision Correction." American Society of Cataract and Refractive Surgery Online. 〈http://www.ascrs.org/eye/refract.html〉.

Snyder, Robert W. "The Differences in Radial Keratotomy Surgery." The University of Arizona Health Sciences Center. 〈http://www.ahsc.arizona.edu/opa/crnap/rk.htm〉.

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Radial Keratotomy

Radial Keratotomy

System of precise predictable keratorefractive surgery

Correcting astigmatism

Possible side effects

Radial keratotomy (RK) is a surgical procedure that reduces myopia (nearsightedness), or astigmatism (diminished focus) by changing the shape of the cornea the outermost part of the eyeball. The procedure is particularly attractive to individuals who want to avoid wearing glasses or wish to be rid of the inconvenience of contact lenses. RK is a quick, relatively painless procedure that takes less than 30 minutes to perform; it is done on an outpatient basis. But while vision can improve immediately, the results may change, sometimes for the worse, over the following several months or years.

First performed in Japan in 1955 by Dr. Tsutomu Sato of Juntendo University, Tokyo, Soviet ophthalmologist Svyatoslav Fyodorov developed the procedure in the 1970s after removing glass splinters from a patient whose vision actually improved once the eye healed. The procedure was brought to the United States in 1977 and further refined. It was first performed in the United States in 1978. Although once

considered a risky procedureand there are still risks involvedmore than one million people worldwide have undergone treatment. In most instances, RK can improve myopic vision to 20/40 or better, even though some cases the patient still needs lenses due to under-correction and in others because of over-correction which causes far-sightedness.

The cornea, the clear cover of the eye, and the lens work together to focus light rays entering the pupil onto the retina, the light sensitive tissue at the back of the eye. The cornea has a natural curve, and the greater the curvature, the greater its refractive power, that is, its ability to bend light so it focuses on the retina.

Normally, pressure inside the eyeball pushes the edges of the cornea forward slightly, flattening the central few millimeters of the cornea and reducing the amount of curvature. Candidates for RK have either excess curvature of the cornea or elongated eyeballs, both of which cause light rays to focus in front of the retina causing myopia. This makes objects at a distance appear blurry.

Astigmatism occurs when the surface of the cornea is not spherical in shape, but has an irregular contour. This makes it difficult to focus clearly on an object, causes a doubling, or ghosting, effect.

Keratotomy, which refers to cutting the cornea, corrects both of these problems by reducing the natural curve of the cornea and slightly flattening it. The reshaped cornea focuses light rays directly on, or very near, the retina, producing a sharper image.

System of precise predictable keratorefractive surgery

American ophthalmologists refined RK and developed newer instruments and techniques to improve results. This refined procedure, called the system of precise predictable keratorefractive surgery, is the standard for this type of surgery. Prospective RK patients must have healthy corneas and be deemed suitable candidates after a pre-surgical examination of the eye. The surgeon measures the curvature of the cornea in order to obtain a baseline from which to determine the amount of flattening that is required. Therefore, patients who wear hard contact lenses must remove them for three weeks before their preoperative eye examination, because the lenses can mold the cornea and change its natural curvature. Patients who wear soft lenses must remove them at least three days before the examination.

On the day of the examination, patients are generally given a sedative to help them relax during the operation, but the surgery itself is painless, and is not done under anesthesia. While on the operating table, the area around the patients eye is cleaned, and topical anesthetic drops are administered to the eye.

The surgeon places an ultrasound probe over the eye to measure the thickness of the cornea in several spots. This measurement is critical, because each incision must penetrate to at least 75% of the depth of the cornea, which is about 0.02 in (0.5 mm) deep, in order to obtain the greatest flattening effect without penetrating the vitreous fluid underneath.

A diamond blade secured within a slot on the handle of the cutting instrument is then adjusted to within a hundredth of a millimeter of the thinnest spot on the cornea. The surgeon then places dark lines on the cornea to guide the blade. Under high magnification with an operating microscope, the surgeon pushes the blade into the cornea with enough force to produce a slight indentation. With the blade adjusted to prevent it from being inserted too deeply, the surgeon then makes a number of incisions in the cornea that radiate from the pupil like the spokes of a wheel, leaving a central clear zone. The patient wears a patch after the operation, and recovery takes about one to two days. When RK is to be done on both eyes, they are operated on during separate visits at least several months apart.

Correcting astigmatism

Astigmatic keratotomy is similar to RK, and is performed to correct astigmatism along with nearsightedness, or when there is only astigmatism. Two incisions are made at the time of RK to flatten the astigmatic part of the cornea.

Although RK has been refined over the years, the results are not perfect in every patient. The ability of surgeons to alter the shape of the cornea is not yet as precise as the ability of lens makers to make a pair of glasses or contact lenses that almost perfectly match the requirements of the wearer.

In addition, the cornea heals slowly after RK, usually becoming flatter as it does so. Thus, some surgeons attempt to compensate for this by undercorrecting the cornea during the operation. Then, as the cornea flattens further during healing, the patients eyes may approach emmetropia, or perfect vision.

Possible side effects

If the patients vision is overcorrected during surgery, post-surgical flattening causes progressive loss of refractive power (ability to bend and focus light rays).Consequently, instead of being myopic (light rays are focused in front of the retina), the eye becomes hyper-opic, or farsighted (i.e., light rays are focused in back of the retina).

As the number of RK patients increased, surgeons encountered an increasing number of potential side effects. Some patients complained of discomfort when in bright light, persistent glare, or disorienting star-like bursts of light when approaching a light at night (e.g., an oncoming vehicles headlights). Moreover, some patients also lost their best correct visual acuity; i.e., their vision was not able to be corrected as well as before RK with properly prescribed glasses or contact lenses. Others suffered infections from micro-organisms that infected the incisions.

A National Eye Institute study, called Prospective Evaluation of Radial Keratotomy (PERK), evaluated 693 patients 10 years after RK procedures were performed in 1982 and 1983 to reduce nearsightedness. Seventy percent did not require corrective lenses for long distance; 85% were corrected to 20/40 or better; 53% to 20/20 or better; and 43% continued to change toward farsightedness; and a significant decrease in vision, even with glasses, occurred in 3% of patients.

In the 1990s, a newer technique, called photoreactive keratectomy (PKR) utilized a type of laser called an excimer laser to decrease nearsightedness. This laser removes a very precise amount of tissue off the center of the cornea using a cold ultraviolet laser, changing the corneal shape to bring the focal point closer to the retina. By the late 1990s, a third correctional device, called the LASIK (LAser in SItu Keratomileusis), was being used. It combines the excimer laser and a microkeratome to also reduce nearsightedness. Although approved by the U.S. Food and Drug Administration (FDA) independently, their combined use is not yet approved. However, in this procedure, the eye is anesthetized and a suction ring centered over the cornea to stabilize the eye. This ring also and provides guide tracks for the microkeratome, a very precise instrument that shaves a micro-thin partial flap off the center of the cornea, leaving it attached at one side like a hinge while exposing the middle portion of the cornea. The excimer laser is then used to remove tissue and reshape the center of the cornea. The flap is replaced and conforms to the flatter, reshaped cornea.

RK surgeries are less frequent in the 2000s due to newer alternatives such as LASIK and PRK that have less complications.

See also Vision disorders.

Marc Kusinitz

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Radial Keratotomy

Radial keratotomy

Definition

Radial keratotomy (RK) is eye surgery performed to correct myopia by changing the cornea's shape.

Purpose

RK was introduced in North America in 1978. RK is one of several surgical techniques for reducing or eliminating the need for corrective lenses. It is most successful in patients with low to moderate nearsightedness—people whose eyes require up to -5.00 diopters of correction.

Precautions

RK cannot help patients whose nearsightedness is caused by keratoconus, a condition in which the cornea is cone-shaped. The procedure usually is not performed on patients under 18 because their vision is unstable. Women who are pregnant, have just given birth, or are breast-feeding should not have RK because hormones may cause temporary corneal changes. Glaucoma patients or patients with any disease that interferes with healing should not have RK.

Radial keratotomy weakens the cornea, making it vulnerable to injuries long after surgery. A head injury after RK can cause the cornea to tear and can lead to blindness. Sports enthusiasts should be warned of this danger.

RK's success cannot be guaranteed. An ophthalmologist estimates the probability of the surgery's success in correcting vision. In some cases, patients with myopia that has caused their near vision to be clear prior to surgery may need corrective lenses for near vision following surgery. Some patients still require lenses for distance vision. RK does not eliminate presbyopia and the eventual need for reading glasses.

Description

With clear vision, light passes through the cornea and the lens of the eye and focuses on the retina. In a myopic patient, the eyeball is usually too long, so that light focuses in front of the retina. RK reduces myopia by flattening the cornea. This flattening reduces the cornea's focusing power, allowing the light to focus further back onto the retina, forming a clearer image.

For RK, a surgeon uses a small diamond-blade knife to make four to eight radial incisions approaching 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.

Before surgery the patient is given a sedative. A local anesthetic—usually eye drops—is used to numb the eye. The patient remains conscious during the procedure. The surgeon utilizes a surgical microscope to magnify the cornea while making the slits. The treatment usually lasts 30 minutes.

Most ophthalmologists perform RK on one eye at a time. Surgeons once thought they could use the results of the first eye to predict how the well the procedure would work on the second eye. However, a study in the American Journal of Ophthalmology in 1997 found that this was not the case. The authors cautioned that there might be other reasons not to operate on both eyes at once, such as increased risk of infection .

RK's costs depends on the surgeon, but usually range from $1,000 to $1,500 per eye. It is usually not covered by insurance.

Preparation

RK patients should be carefully screened by an ophthalmic assistant or physician before surgery is approved to avoid possible complications. This screening should include a comprehensive eye exam, either by the ophthalmologist, or a co-managing optometrist at least a few days before surgery. At this time, the physician or ophthalmic

assistant should chart any dry eye or any corneal disease that may hinder surgery. They also should perform corneal topography, which creates a map of the patient's eye.

Assistants must advise patients to discontinue wearing contact lenses weeks prior to the visual exams to make sure vision is stable; and they must also advise the doctor of contact lens wear.

Before surgery, ophthalmic staff administer eye drops and a sedative to the patient. The physician tests the patient's vision, and the patient rests while waiting for the sedative to take effect. Immediately before the surgery, ophthalmic staff administer local anesthetic eye drops.

Before beginning the procedure, the surgeon measures the cornea's thickness to decide how deep the slits should be, and marks an area in the center of the cornea called the optical zone. This is the part of the cornea in the area over the pupil that the patient sees through. No cuts are made in this region.

Aftercare

After surgery, some patients feel pain and are given eye drops and medications to relieve discomfort. For several days the eye may feel scratchy and look red. This is normal. The eye also may water, burn, and be sensitive to light.

Patients should be advised to use eye drops for several weeks to protect against infection. Patients also should be told to protect the head and eyes.

The cornea heals slowly, and full recovery can take months. This is one reason RK has fallen out of favor with surgeons and patients. Laser-refractive surgeries, such as laser-assisted in situ keratomileusis (LASIK), have better results with faster recovery. Such procedures as LASIK and corneal rings have rendered RK virtually obsolete.

While the cornea is healing, patients may experience better eyesight in the morning than in the evening (or vice versa); pain; glare; starburst or halo effects; or a hyperopic shift. As the cornea flattens, vision may become more hyperopic. For this reason, the surgeon may initially undercorrect the patient. This gradual shift may occur over several years. This procedure leaves permanent scars on the cornea.

If RK does not completely correct nearsightedness, corrective lenses may be needed. Presbyopic patients will still require reading glasses.

Patients return to the surgeon for a follow-up exam one day post-operatively. After that, patients may be referred to the co-managing optometrist for the subsequent three or four visits. Patients should be advised to report any pain or nausea immediately to the attending physician.

Complications

Complications from RK include:

  • cataract
  • infection
  • lasting pain
  • tears along an incision, especially after being hit in the head or eye
  • vision loss
  • hyperopic shift

Complications are reduced when an ophthalmologist experienced with RK performs the surgery. Younger patients also tend to heal faster.

Results

The desired result of radial keratotomy is myopia reduction. A study reported by the National Eye Institute in 1994 tracked the success of 374 patients who had RK 10 years earlier. The study found that:

  • 85% had at least 20/40 vision
  • 70% did not need corrective 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

Health care team roles

Allied health professionals help prepare patients for refractive surgery. Advanced and intermediate level ophthalmic technicians perform refractions and help determine the patient's eligibility for surgery. These professionals also may perform corneal topography.

Specially trained ophthalmic nurses assist during surgery. They prepare the operating room and equipment, and administer eye drops. Advanced ophthalmic technologists, who are trained for such additional duties as taking ophthalmic photographs and using ultrasound, may administer eye medications, perform tests, maintain surgical equipment and assist in refractive surgery.


KEY TERMS


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 microkeratone to change the shape of the cornea.

Local anesthetic —Used to numb an area in which 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.


Training

The American Society of Cataract and Refractive Surgery keeps physicians informed of the latest advances in surgery. Optometrists are advised to observe surgeries and attend seminars to learn more about follow-up treatments.

Ophthalmic assistants who want to assist in these surgeries can receive additional training from certified education programs.

Resources

PERIODICALS

Azar, Dimitri, M.D.; Khoury, Johnny. M.D. "Understanding Wound Healing After Refractive Surgery." Review of Ophthalmology Online <http://www.revophth.com/RPC5F9.HTM>.

Brown, David C., M.D. "How to Diversify." Ophthalmology Management Online <http://www.ophmanagement.com/archive_results.asp?loc=archive/11119934028pm.html>.

Feldman, Miriam Karmel. "Cataract Warning: RK Patients Need Special Care." EyeNet Magazine Online <http://www.eyenet.org/eyenet_mage/02_00/cataract.html>.

Koffler, Bruce H., M.D. "Post-Op Strategies." Ophthalmology Management Online <http://www.ophmanagement.com/archive_results.asp?loc=archive/1180041950pm.html>.

ORGANIZATIONS

American Academy of Ophthalmology. P.O. Box 7424, San Francisco, CA 94120-7424. (415) 561-8500. <http://www.eyenet.org>.

American Optometric Association. 243 N. Lindbergh Blvd., St. Louis, MO 63141. (314) 991-4100. <http://www.aoanet.org/aoanet/>.

American Society of Cataract & Refractive Surgery. 4000 Legato Road, Suite 850, Fairfax, VA 22033. (703) 591-2220. <http://www.ascrs.org>.

OTHER

"Refractive Surgery: New Options in Vision Correction" American Society of Cataract and Refractive Surgery Online. <http://www.ascrs.org/eye/refract.html>.

Snyder, Robert W. "The Differences in Radial Keratotomy Surgery." The University of Arizona Health Sciences Center. <http://www.ahsc.arizona.edu/opa/crnap/rk.htm>.

Mary Bekker

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Radial Keratotomy

Radial keratotomy

Radial keratotomy (RK) is a surgical procedure that reduces myopia (nearsightedness), or astigmatism (diminished focus) by changing the shape of the cornea—the outermost part of the eyeball. The procedure is particularly attractive to individuals who want to avoid wearing glasses or wish to be rid of the inconvenience of contact lenses. RK is a quick, relatively painless procedure that takes less than 30 minutes to perform; it is done on an outpatient basis. But while vision can improve immediately, the results may change, sometimes for the worse, over the following several months or years. RK was first attempted in Japan in 1939, then refined during the 1960s and 1970s in the Soviet Union, and first performed in the United States in 1978.

The cornea, the clear cover of the eye , and the lens work together to focus light rays entering the pupil onto the retina, the light sensitive tissue at the back of the eye. The cornea has a natural curve , and the greater the curvature, the greater its refractive power, that is, its ability to bend light so it focuses on the retina.

Normally, pressure inside the eyeball pushes the edges of the cornea forward slightly, flattening the central few millimeters of the cornea and reducing the amount of curvature. Candidates for RK have either excess curvature of the cornea or elongated eyeballs, both of which cause light rays to focus in front of the retina causing myopia. This makes objects at a distance appear blurry.

Astigmatism occurs when the surface of the cornea is not spherical in shape, but has an irregular contour. This makes it difficult to focus clearly on an object, causes a doubling or "ghosting" effect.

Keratotomy, which refers to cutting the cornea, corrects both of these problems by reducing the natural curve of the cornea and slightly flattening it. The reshaped cornea focuses light rays directly on, or very near, the retina, producing a sharper image.


System of precise predictable keratorefractive surgery

American ophthalmologists refined RK and developed newer instruments and techniques to improve results. This refined procedure, called the system of precise predictable keratorefractive surgery, is the standard for this type of surgery. Prospective RK patients must have healthy corneas and be deemed suitable candidates after a presurgical examination of the eye. The surgeon measures the curvature of the cornea in order to obtain a baseline from which to determine the amount of flattening that is required. Therefore, patients who wear hard contact lenses must remove them for three weeks before their preoperative eye examination, because the lenses can mold the cornea and change its natural curvature. Patients who wear soft lenses must remove them at least three days before the exam.

On the day of the examination, patients are generally given a sedative to help them relax during the operation, but the surgery itself is painless, and is not done under anesthesia . While on the operating table, the area around the patient's eye is cleaned, and topical anesthetic drops are administered to the eye.

The surgeon places an ultrasound probe over the eye to measure the thickness of the cornea in several spots. This measurement is critical, because each incision must penetrate to at least 75% of the depth of the cornea, which is about 0.02 in (0.5 mm) deep, in order to obtain the greatest flattening effect without penetrating the vitreous fluid underneath.

A diamond blade secured within a slot on the handle of the cutting instrument is then adjusted to within a hundredth of a millimeter of the thinnest spot on the cornea. The surgeon then places dark lines on the cornea to guide the blade. Under high magnification with an operating microscope , the surgeon pushes the blade into the cornea with enough force to produce a slight indentation. With the blade adjusted to prevent it from being inserted too deeply, the surgeon then makes a number of incisions in the cornea which radiate from the pupil like the spokes of a wheel, leaving a central clear zone. The patient wears a patch after the operation, and recovery takes about one to two days. When RK is to be done on both eyes, they are operated on during separate visits at least several months apart.


Correcting astigmatism

Astigmatic keratotomy is similar to RK, and is performed to correct astigmatism along with nearsightedness, or when there is only astigmatism. Two incisions are made at the time of RK to flatten the astigmatic part of the cornea.

Although RK has been refined over the years, the results are not perfect in every patient. The ability of surgeons to alter the shape of the cornea is not yet as precise as the ability of lens makers to make a pair of glasses or contact lenses that perfectly match the requirements of the wearer.

In addition, the cornea heals slowly after RK, usually becoming flatter as it does so. Thus, some surgeons attempt to compensate for this by undercorrecting the cornea during the operation. Then, as the cornea flattens further during healing, the patient's eyes may approach emmetropia, or perfect vision.

Possible side effects

If the patient's vision is overcorrected during surgery, postsurgical flattening causes progressive loss of refractive power (ability to bend and focus light rays). Consequently, instead of being myopic (light rays are focused in front of the retina), the eye becomes hyperopic, or farsighted (i.e., light rays are focused in back of the retina).

As the number of RK patients increased, surgeons encountered an increasing number of potential side effects. Some patients complained of discomfort when in bright light, persistent glare, or disorienting starlike bursts of light when approaching a light at night (e.g., an oncoming vehicle's headlights). Moreover, some patients also lost their best correct visual acuity, i.e., their vision was not able to be corrected as well as before RK with properly prescribed glasses or contact lenses. Others suffered infections from microorganisms that infected the incisions.

A National Eye Institute study, called Prospective Evaluation of Radial Keratotomy (PERK), evaluated 693 patients 10 years after RK procedures were performed in 1982 and 1983 to reduce nearsightedness. Seventy percent did not require corrective lenses for long distance; 85% were corrected to 20/40 or better; 53% to 20/20 or better; and 43% continued to change toward farsightedness; and a significant decrease in vision, even with glasses, occurred in 3% of patients.

In the 1990s, a newer technique, called Photoreactive Keratectomy (PKR) utilized a type of laser called an excimer laser to decrease nearsightedness. This laser removes a very precise amount of tissue off the center of the cornea using a "cold" ultraviolet laser, changing the corneal shape to bring the focal point closer to the retina. By the late 1990s, a third correctional device, called the LASIK (LAser in SItu Keratomileusis), was being used. It combines the excimer laser and a microkeratome to also reduce nearsightedness. Although approved by the FDA independently, their combined use is not yet approved. However, in this procedure, the eye is anesthetized and a suction ring centered over the cornea to stabilize the eye. This ring also and provides "guide tracks" for the microkeratome, a very precise instrument that "shaves" a micro-thin partial flap off the center of the cornea, leaving it attached at one side like a hinge while exposing the middle portion of the cornea. The excimer laser is then used to remove tissue and reshape the center of the cornea. The flap is replaced and conforms to the flatter, reshaped cornea.

See also Vision disorders.

Marc Kusinitz

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