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Ten-Year Results on Radial Keratotomy Released

October 13, 1994

After a decade of patient follow-up, a National Eye Institute (NEI)-supported study reported today that radial keratotomy (RK) remained a reasonably safe and effective technique to improve distance vision.

However, the study found that more than 40 percent of RK-operated eyes continued to have a gradual shift toward farsightedness. This finding suggests that some people who have RK may need glasses at an earlier age for poor close-up vision, a common problem after age 40, than if they had chosen not to have the surgery.

“Based on these findings, it may be that some people will be pleased with their vision shortly after having RK, but their opinion may change five, ten, or fifteen years down the road,” said PeterJ. McDonnell, M.D., of the Doheny Eye Institute at the University of Southern California and the study’s co-chairman.

Today’s findings, published in Archives of Ophthalmology, were issued from the Prospective Evaluation of Radial Keratotomy (PERK). The PERK study is the first large, well-designed clinical study to evaluate the long-term effects of radial keratotomy on the eye and vision.

RK is performed to improve poor distance vision, called myopia, which affects millions of Americans. For some people with myopia, RKoffers the prospect of good distance vision without the need for glasses or Contact lenses.

The surgery changes the shape of the cornea, the clear, rounded tissue at the front of the eye. It is performed by making spoke-like,partial-thickness incisions into the healthy cornea. These wounds cause the cornea to flatten, producing clearer distance vision.

Today, about 250,000 RK surgeries are performed annually in theUnited States, up from 30,000 operations just five years ago. However, eye care professionals still have little scientific information about the procedure’s long-term effects on the cornea and vision.

To provide these data, PERK clinicians periodically examined the eyes of the 435 participants since the study began in the early 1980s. Based on these examinations, researchers have published occasional reports in medical journals, including the results issued today.

At the PERK’s 10-year mark, researchers reported that RK effectively reduced but did not completely eliminate myopia in all patients. They found that 53 percent of the RK-operated eyes registered 20/20 vision, while 85 percent of the eyes had 20/40 uncorrected vision or better(required for a driver’s license in most states). Approximately a 70percent of study participants said they did not wear corrective lenses for distance vision at the 10-year mark.

RK also had “a reasonable margin of safety,” resulting in few vision-threatening complications. However, the researchers noted that 3 percent of operated eyes had poorer distance vision with glasses one decade after surgery, although none had corrected vision worse than 20/30.

Interestingly, the PERK scientists reported that 43 percent of the theRK-operated eyes continued to have a gradual change toward farsightedness, called hyperopic shift. In fact, 36 percent of the eyes had become farsighted at the 10-year point.

“Typically, people who are myopic need reading glasses later in life than those who are not myopic,” said Dr. McDonnell. “It may be that some people will reduce their need for glasses to see at a distance, but will need to wear reading glasses earlier than they otherwise would have needed to.”

But the hyperopic shift was beneficial in some cases. In those who remained nearsighted after surgery, this gradual change caused an improvement in their vision, moving their sight closer to 20/20.

According to the researchers, this shift was detected in some affected patients as soon as six months after surgery and continued to progress a decade later. They said they do not know when and if thisvchange will cease in the future.

The scientists noted that the shift in vision was not related to the patient's age or post-surgical outcome. They added that they could not predict based on the PERK data which patients will develop the hyperopic shift. They did note, however, that the shift was more common in those who had RK surgery using longer incisions in the cornea, a common technique in younger and/or more myopic patients.

“This clinical study provides ophthalmologists with scientifically validated information regarding the safety and effectiveness of radial keratotomy, said Carl Kupfer, M.D., director of the NEI, part of the National Institutes of Health. “With these results, prospective patients can have the best informed consent when considering radial keratotomy.”

The National Eye Institute is the Federal government’s lead agency for vision research.


The PERK is a prospective clinical study involving 435 patients at nine centers nationwide. It was designed to evaluate the short and long-term safety and efficacy of one standardized RK technique. The procedure was evaluated by comparing each patient’s refractive error and uncorrected vision before and after surgery.

The RK technique used in the study consisted of eight centrifugal, radial incisions made manually with a diamond micrometer knife.

All study participants were at least 21 years old and had myopia(two to eight diopters) that was correctable to 20/20 or better with glasses or Contact lenses. Each patient agreed to have RK performed on one eye and wait one year before having surgery on their other eye.

Participants were examined before and after surgery at two weeks, three months, six months, annually for five years, and again at 10years.

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  • Waring GO 3rd, Lynn MJ, McDonnell PJ. Results of The Prospective Evaluation of Radial Keratotomy (PERK) Study 10 years After Surgery. Arch Ophthalmol. 1994 Oct. PubMed