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RK, PRK, both, neither?
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VENTURA, Calif.—Refractive surgeons with experience in both incisional and laser surgery say they will continue to perform radial keratotomy, at least for certain indications, for the foreseeable future. They say RK for low myopia has results as good as, if not better than, photorefractive keratectomy (PRK). And teachers say their course enrollments indicate that incisional refractive surgery procedures are gaining new practitioners all the time.
In fact, one surgeon believes RK is so robust, it will not only coexist with PRK surface-ablation techniques but outlast them, surviving to become a complementary procedure to laser in situ keratomileusis (LASIK).
Some surgeons worry that the marketing hype for PRK that will undoubtedly follow Food and Drug Administration (FDA) approval of the procedure will make it harder for them to convince patients that RK is more in their interest than PRK for certain indications.
But the refractive surgeons interviewed for this article said they would continue to recommend RK and, even more so, astigmatic keratotomy (AK) for correction of a range of refractive errors. They said RK and AK would remain viable as primary procedures for correction of low to moderate myopia and astigmatism, and as secondary procedures to enhance unsatisfactory results of PRK.
Effect on optometry
How will the advent of PRK and the status of RK affect optometric referral patterns for refractive surgery? If you are currently sending patients to an incisional refractive surgeon, should you be looking for a laser surgeon?
The best advice from the surgical side seems to be to work with a surgeon who can offer comprehensive refractive surgery: someone who can perform a variety of incisional procedures and who also has access to a refractive laser. Surgeons who offer only laser refractive procedures will not have enough depth of experience to offer complete refractive surgical care to patients.
"Any good refractive surgeon will tell you that, even if you are a proponent of PRK, you still need to be good at incisional refractive surgery, at least for addressing astigmatism," said David R. Shapiro, MD, of Ventura, Calif.
"You have to be a comprehensive refractive surgeon," he said. "To do only laser and not back it up with incisional surgery is like going out in a boat without knowing how to swim."
Shapiro, whose practice is entirely devoted to refractive surgery, said that assuming PRK will be a "push-button panacea" can get surgeons—as well as optometrists—into trouble.
"You can box yourself into a corner," he explained, "by saying, 'Oh, you don't want that old RK, it's a dinosaur.' If a patient is corrected from –5 D to –1 D by PRK, he could then benefit from a little RK touch-up. But if you've already told the patient how barbaric it is to put incisions in the cornea, you are forced to reablate, instead of doing a very simple RK enhancement. You could end up doing something that is not in the best interest of the patient."
--- Richard L. Lindstrom, MD
Richard L. Lindstrom, MD, of Minneapolis, a refractive surgeon with years of experience in both incisional and laser surgery, agreed. "With a one- or two-incision RK we can correct up to about 2 D of residual myopia after PRK, and if we put those incisions in the steeper meridian we can also correct astigmatism," he said. "The procedure takes about five minutes, the patient sees better in five minutes, and it's a very nice enhancement. For me, that is better than exposing the patient to another PRK or LASIK procedure."
Indications for primary RK
Aside from its role as an enhancement, RK will continue to be many surgeons' procedure of choice for primary correction of low to moderate myopia. Surgeons vary in their opinions on the upper limit of correction, but all see a continued role for the knife.
--- Spencer P. Thornton, MD
Spencer P. Thornton, MD, of Nashville, Tenn., a pioneer of incisional refractive techniques, said he will be correcting up to 5 D of myopia with RK well after PRK approval. "RK will still be the main means of correcting errors up to 5 D, and in most cases above that PRK will probably be the way to go," he said. "RK is predictable, and we have few problems with it. With the American technique, the likelihood of getting full correction with one or two procedures is very high, about 95%. And AK remains the surest way of correcting astigmatism."
Lindstrom said he would continue to recommend RK for patients in the range of –1 D to –3 D. He cited results of a poll of International Society of Refractive Surgery members, indicating that about three-fourths of respondents who currently perform RK will continue to do so for –1 D to –3 D, despite the existence of effective laser refractive procedures.
--- Yair Karas, MD
In Toronto, a hotbed of PRK and LASIK activity, Yair Karas, MD, said he continues to recommend RK for errors up to –6 D. "In the –6-D to –8-D range, I can see the advantages to PRK, but I continue to prefer RK because I get very good results, and the percentage of scarring and regression after PRK is certainly much higher," he said.
Shapiro said RK will remain his choice up to "the dioptric correction that can be achieved with a 2.75-mm optical zone." He said he uses that nomenclature, rather than a dioptric limit, because RK is a highly age-dependent procedure. "For an older patient, that could be up to –9.5 D, for a younger patient up to –5.5 D," he said.
--- James J. Salz, MD
A study by James J. Salz, MD, found similar outcomes in RK and PRK patients for corrections of –1 D to -6 D. At one year, 94% of RK patients and 90% of PRK patients had uncorrected vision of 20/40 or better, he said. The major difference between the groups was the number of procedures needed to achieve that result; RK patients needed an average of 1.5 procedures per eye, while PRK patients needed only one procedure. "I think there will still be a role for both procedures," Salz said. "Surgeons can go ahead and get on line for the excimer, but they should keep the diamond knife handy as well."