Radial Keratotomy (RK)
Definition
Radial keratotomy (RK) is a refractive surgery procedure in which small incisions are made in the cornea to help correct refractive error and decrease or eliminate the need for glasses or contact lenses in myopic (nearsighted) individuals. Radial keratotomy was one of the first refractive surgery procedures to be widely used for vision correction since its development in the 1960s and 70s. However, it has largely been replaced today by technologies that allow for greater precision, such as LASIK and PRK.
How Does RK Work?
In RK surgery, small, partial thickness incisions are made in a radial fashion around the center of the cornea, like spokes on a wheel.
These incisions allow the peripheral cornea to expand somewhat, leading to a flattening of the central corneal curvature. This central flattening is helpful in correcting nearsighted eyes, in which the central cornea is too steeply curved. By flattening the central cornea, light coming into a nearsighted eye is more sharply focused on the retina and the vision becomes clearer. RK is effective only for lower levels of myopia.
Who are candidates for RK?
RK helps correct the vision of people with myopia. Similar partial thickness incisions in a curved fashion on the edge of the cornea, called astigmatic keratotomy, can also help correct some forms of astigmatism. RK is uncommonly used today, as it has largely been replaced by excimer laser surgeries, which are more precise, and result in more predictable outcomes. RK is sometimes still performed today as a primary refractive surgery technique in some patients, or as an enhancement technique after other forms of refractive surgery have been performed.
In general, candidates for RK should be:
- 21 years of age or older: younger people may still have eyes that are growing.
- Dissatisfied with wearing glasses or contact lenses.
- Have had no change in glasses or contact lens prescription for at least a year.
- Have otherwise healthy eyes.
- Be willing to accept a small amount of risk associated with surgery.
- Understand that glasses and/or contacts are occasionally still needed for some activities after surgery.
- Not have excessively thin corneas or extremely high levels of refractive error. Your doctor will test for these conditions on your evaluation exam.
- Have a relatively low level of nearsightedness to correct, ranging from -1.0 to -4.00 diopters
These conditions may prevent you from undergoing RK or other corneal refractive surgeries. You should alert your eye surgeon if you have one or more of these conditions so that he or she can help you make the best choice about undergoing refractive surgery:
Condition:
Reason for caution:
Examination prior to RK
Before you arrive at the doctor's office
If you wear contact lenses you must stop wearing them prior to surgery–at least two weeks for soft contacts and one month for hard contacts. This is because contact lenses can cause mild warping of the corneal shape, which may interfere with the preoperative measurements of the eye and calculations for refractive surgery.
Tests you may have at the doctor's office
The evaluation for RK surgery typically includes a complete eye exam of the front and back of the eye, plus several additional tests including:
- Your vision with and without glasses will be tested, as well as a refraction to determine if your current vision differs markedly from the vision corrected in your current glasses. If they do differ markedly, you may need to return for another visit several weeks later for a repeat refraction to insure that your prescription is not changing.
- The thickness of your corneas will also be tested. Since these surgeries remove some corneal tissue during the reshaping process of vision correction, a minimum amount of corneal thickness is required.
- Your pupil size will also be examined. People with large pupils may be at increased risk for night vision symptoms, such as glare and halos, after refractive surgery.
- Lastly, several machines may be used to assess the shape of your cornea, including a topographer and/or a tomographer, and possibly a wavescan abberometer. Your doctor will review the information from these machines in order to determine if your corneas are regularly shaped. Individuals with abnormally shaped corneas may not be ideal candidates for refractive surgery due to a possible increased risk of irregular corneal warpage after the surgery. Your doctor will have a detailed discussion about any abnormal corneal findings with you and help you choose the best option for your vision correction.
Is 20/20 vision guaranteed with RK?
Though RK is helpful in correcting myopia, its results are somewhat variable. Less people achieve 20/20 vision or better with this technique than with excimer laser surgeries. In fact, in a large clinical trial of RK conducted in the early 1980's, only 53% of patients achieved 20/20 vision or better.
Additional incisions may be required if the initial incisions in the cornea fail to appropriately correct the vision. RK may lead to fluctuation of vision through the day and night vision symptoms such as glare, starbursts and halos. The majority of patients undergoing RK have improved uncorrected vision from the procedure and decreased dependence on glasses and contacts; however, the vision they obtain without glasses after the procedure may not be as crisp as that which they enjoyed while wearing glasses or contacts alone. Lastly, the results of RK are not as stable over time as LASIK or PRK, with many eyes experience a slow progression towards hyperopia over years after the surgery.
What are the risks of RK?
The risks of these surgeries fall into two main categories: Vision Loss Risks, and Nuisance Risks.
Vision Loss Risks
Vision loss may occur after RK refractive surgery. Though rare, these risks include:
- Infection: Since cuts are made on the eye, it is possible that bacteria could gain access to the corneal tissue and start an infection. Scarring from such an infection could lead to vision loss. This is very uncommon as powerful antibiotics are used after surgery to prevent infection. The risk of severe infection is less than 1 in 500.
- Irregular Astigmatism: The incisions of RK occasionally cause irregular astigmatism, which is astigmatism that is not corrected well by glasses or soft contact lenses. A hard contact lens or additional Wavefront refractive surgery with the excimer laser can treat irregular astigmatism and restore the vision.
- Scarring: Since RK uses incisions to change the shape of the cornea, scarring may occur and lead to a loss of vision. This is especially true when the RK incisions are very close to the center of the cornea.
- Progressive Corneal Warpage (Ectasia): In this condition, the cornea begins to warp in odd directions, leading to loss of vision. Occasionally, a corneal transplant is required. Ectasia, however, is typically only seen in patients with abnormal corneal shapes, or corneal dystrophies such as keratoconus; its likely these conditions exist even before the surgery is done. Your surgeon will screen your corneas to help identify any preexisting corneal shape irregularity. The risk of Ectasia is less than 1 in 3500.
Nuisance Risks
Most of the other risks associated with RK surgery don't usually cause a significant loss of vision. Rather, they can cause nuisance problems with the eyes that may not have been present before the surgery.
- Fluctuation of vision: Some individuals experience sharper vision at various parts of the day after RK surgery. This is related to swelling of the cornea that occurs overnight, then progressively resolves as the day goes on. In most cases, the degree of fluctuation is mild, and most only a nuisance.
- Night Vision Symptoms: Some patients notice their night vision is different post-surgery. Usually, this occurs in the form of halos around streetlights, added glare from oncoming traffic, or increased difficulty seeing dimly light shapes in the dark. Medications can be used to change the size of the pupil in low light or nighttime settings, which can help reduce night vision symptoms if they occur.
- Regression of Effect and Enhancements: RK has proven to be unstable over time in some patients. Typically, these eyes may become more hyperopic (farsighted) over time and may require further refractive surgery or glasses and contacts to correct. Further, as RK relies on the surgeon's hand for delivering the refractive correction, it is less precise than refractive surgeries that use the excimer laser. As such, over or under correction sometimes occurs even with the initial procedure. If this happens, an enhancement procedure can be done several times to correct the remaining refractive error. Enhancement procedures carry a small risk of all of the above complications, just like the original procedure.
What will I experience during the RK procedure?
On the morning of your procedure, your surgeon will ask you not to wear any makeup (which may stain the cornea) or perfume or cologne. At the laser surgery center, you will usually be given a Valium pill to help you feel calm during the procedure. You lie on a special bed, and the procedure itself usually takes less than 10 minutes an eye. A blinking red light serves as your target to focus on during the procedure. A lid holder is used to hold your eyelids open, and numbing drops are placed on the eye. Then the surgeon uses a very fine diamond tipped knife to create the RK incisions. Last, eye drops are placed in the eye.
After the procedure is done, your surgeon may examine your eye, or simply have you go home and take a long nap. Your eyes will start to burn and feel irritated about half an hour after the surgery as the numbing medicine wears off. The nap, plus the eye drops your surgeon will give you helps make your eyes feel more comfortable.
Your doctor will see you the next day, at which point the eyes feel more comfortable. You typically see your doctor again in about a week to assess the healing of the surface cells and remove the contact lens. You will continue using eye drops for several weeks after the surgery, and then see your doctor again in about a month for a vision check. If all is well, as it typically is, your doctor will usually see you again in 6 months to a year for another vision check. During the few months after the surgery, artificial tears should be used regularly to help limit dryness of the eyes while they heal.
