radial keratotomy

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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.

keratotomy

 [ker″ah-tot´ah-me]
incision of the cornea.
radial keratotomy an operation in which a series of incisions is made in the cornea from its outer edge toward its center in a spokelike fashion; done to flatten the cornea and thus to correct myopia.
Radial keratotomy. A, Before procedure. B, Incisions are made from the center to the periphery. C, The corneal contour is flattened.

ra·di·al ker·a·tot·o·my

a keratotomy with radial incisions around a clear central zone. A form of refractive keratoplasty used in the treatment of myopia.

radial keratotomy

n. Abbr. RK
Keratotomy involving a radial pattern of incisions, used to reduce or correct myopia.

radial keratotomy (RK)

a surgical procedure in which a series of tiny shallow incisions is made in the cornea to flatten it, thereby reducing refractive error. The operation is performed using local anesthesia and requires only 10 minutes. Hospitalization is not necessary. Radial keratotomy usually corrects mild to moderate myopia. Compare photorefractive keratectomy. See also refractive keratotomy.
enlarge picture
Location of incisions in radial keratotomy

radial keratotomy

Ophthalmology A form of refractory surgery–a technique for correcting myopia by changing corneal conformation, causing it to flatten, ↓ myopia Complications Daily fluctuation in visual acuity, visual haziness, glare and halos, overcorrection, undercorrection, bacterial keratitis or endophthalmitis, corneal perforation, recurring corneal erosion and scarring, irregular astigmatism, cataract formation Contraindications Corneal dystrophy, ocular surface disease, corneal scarring. See Laser Eye Surgery.  Cf LASIK, Photoreactive keratectomy.

ra·di·al ker·a·tot·o·my

(rā'dē-ăl ker'ă-tot'ŏ-mē)
A form of refractive keratoplasty used in the treatment of myopia.

radial keratotomy

An eye operation in which eight or more radiating cuts are made in the outer zone of the CORNEA so as to produce scars that flatten the curvature and reduce short sight (MYOPIA). The results are uncertain and the operation has been criticised. It has been largely replaced by excimer laser corneal reshaping.

keratotomy, radial (RK)

A surgical procedure on the cornea aimed at correcting ametropia. It consists of making incisions in the anterior part of the cornea in order to flatten it and thereby produce a reduction of its power. The incisions are usually radial, extending from the limbus to about halfway towards the centre like the spokes of a wheel, but other patterns of incision are also used. In some cases, the procedure does not produce a perfect correction and vision is poor, especially in the dark. The use of the excimer laser provides greater accuracy and success. The technique is then called laser refractive keratoplasty (LRK) or photorefractive keratectomy (PRK). Syn. refractive keratoplasty and keratorefractive surgery (both terms also include epikeratoplasty, keratomileusis and keratophakia). See cornea; epikeratoplasty; photorefractive keratectomy; keratomileusis; keratophakia; keratoreformation; LASEK; LASIK.

ra·di·al ker·a·tot·o·my

(rā'dē-ăl ker'ă-tot'ŏ-mē)
A form of refractive keratoplasty used in the treatment of myopia.

radial keratotomy (ker´ətot´əmē),

n a surgical procedure in which a series of tiny, shallow incisions are made on the cornea, causing it to bulge slightly to correct for nearsightedness. The operation is performed using local anesthesia and requires only a few minutes. Hospitalization is not necessary. Radial keratotomy usually corrects mild to moderate myopia.