Radial keratotomy, or RK, involves the precise placement of microscopic incisions in the cornea to change its curvature. The object of the procedure is to flatten the cornea and thereby correct the nearsightedness by allowing rays of light to focus properly on the retina.
Before undergoing RK, the patient will receive a complete eye exam. Corneal curvature, astigmatism, intraocular pressure, and the thickness of the cornea are measured and recorded. Also, the eyes are carefully examined for signs of disease or indications of future problems. Using this information and data regarding the patient's age and sex, some surgeons use a sophisticated computer program that provides guidelines for the number, depth, length, and position of the keratotomy incisions. This computer program has greatly improved the precision and predictability of the radial keratotomy procedure.
During the procedure, a series of four to 16 or more tiny incisions are placed in the mid-periphery or outer portion of the cornea with a precise diamond-edged knife. These incisions go only part way through the cornea and are not intended to obstruct the normal viewing zone of the eye. These incisions are so superficial that major anesthesia is not required. However, a drop of topical anesthetic placed in the eye (or a local anesthetic) makes the procedure virtually painless.
Once the patient is comfortable and the eye numbed by the topical anesthetic, a lid speculum is put in place to retract the eyelids. Viewed through an operating microscope, the optical center of the eye is carefully marked. To correct for myopia, the radial keratotomy incisions will extend between the border of the clear optical zone centrally and the out aspect of the cornea peripherally, leaving the center of the cornea free from incisions. Before the incisions can be placed, however, the knife used in making them is precisely set under the operating microscope. The instrument has a guard on it so that the correct incision depth will be achieved. The diamond radial keratotomy instrument is generally preferred over steel instruments because most surgeons in the U.S. feel it ensures the most predictable results.
While the eye is steadied with a pair of forceps, four to sixteen or more radial cuts are made in such a way as to avoid extending the cuts beyond the edge of the cornea. If significant astigmatism is present, additional radial or transverse incisions may be made during the initial procedure or later, after the eye has healed. For patients with severe astigmatism, incisions may be placed in a step-ladder-like fashion. These incisions are made perpendicular to the direction of the steepest corneal curvature, along the surface that is to be flattened during the operation. Each of these techniques will relax the steeper meridian to match the curvature of the cornea in the other direction and promote a new corneal surface that is properly rounded.
Although rare, side effects from RK can occur. They may include:
- Fluctuating vision, especially during the first few months after surgery
- A weakened cornea, more vulnerable to rupture if hit directly
- Difficulty in fitting contact lenses
- Glare or starburst around lights that can sometimes be permanent
- Light sensitivity
Radial keratotomy was once one of the most frequently used surgical procedures to correct nearsightedness. However, since the development of more effective vision repair procedures, such as LASEK, LASIK and PRK, RK is rarely used today.