Although LASIK is still the king of refractive surgery in general, PRK still has a significant place in today’s mix of refractive surgery procedures for the foreseeable future—and is sometimes used even more often than before. In this article, surgeons explain how they position the procedure and why they rely on it in a variety of cases. They also offer advice to help you determine which patients benefit the most from the procedure.
One and Only
Farrell C. Tyson, MD, FACS, of Tyson Eye in Cape Coral, Florida, knows of surgeons in his region who offer PRK as their only form of refractive surgery. “We’ve seen a number of colleagues go full circle,” he says. “I believe they don’t want to deal with flap complications. Plus, PRK is more cost-effective. We see practices promote it as ‘bladeless laser vision correction,’ giving it the aura of a new innovation.”
Not everyone agrees with this approach, however. Unlike some refractive surgeons, Arturo S. Chayet, MD, the medical director of Codet Vision Institute, Tijuana, Mexico, doesn’t think the term PRK stigmatizes the procedure or suggests that it’s outdated, even though the procedure is more than 25 years old. “To call PRK by an alternative name, such as advanced surface ablation or bladeless refractive surgery, is a big mistake, creating confusion,” he says. “We always call it PRK at our practice. We make sure the patient understands that we offer state-of-the-art PRK and state-of-the-art LASIK.”
At Tyson Eye, meanwhile, Dr. Tyson also sticks to the PRK label, using the procedure in about 5 percent of all of the refractive surgeries he performs. Generally, he says he reserves it for conditions that are causing irregular corneas, such as epithelial basement membrane dystrophy. Besides creating a refractive result, he notes that PRK on these patients enables him to buff down irregularities in the anterior corneal layer.
“One recent case we had is an example of when PRK can be most helpful,” says Dr. Tyson. “We did keratometry, and you could see slight steepening of the cornea, inferiorly. That’s when I decided to switch to PRK. The patient in question had forme fruste keratoconus.”
Dr. Tyson says he also turns to PRK when a post-RK patient presents for repeat refractive surgery. “We get a lot of patients who come in as post-RK cases,” he says. “I don’t want to make a deep-flap cut on them. I’d rather buff out the residual refraction. PRK enables me to do that cleanly.”
Even Daniel S. Durrie, MD, who co-created sub-Bowman’s keratomileusis and now offers every type of refractive surgery, finds a place for PRK in his practice. “Looking back over the past 10 years at our practice, I’d say the percentage of patients undergoing PRK has been very stable at 10 to 15 percent,” says Dr. Durrie, who runs Durrie Vision in Overland Park Kansas. “The main indications are pre-existing epithelial disease or thin corneas.”
Deciding Between LASIK and PRK
Many refractive surgeons lean toward LASIK. “Recovery from LASIK is a lot nicer and slicker than PRK,” says William Bond, MD, FASC, medical director of Bond Eye Associates in Peoria and Pekin, Illinois. “But there’s always that moment of truth when you’re making the flap. You’ve got to get the eye more wide-open. And there’s the possibility of a flap problem or some complication that you just won’t get with PRK. For example, I’ll choose PRK for the patient with a small orbit, where the strong bone structure is in the way and I can’t get the eye open enough. That makes me worry that I’m going to have a problem with suction.”
Also, he continues, “I watch for a residual bed that’s too thin for LASIK. We have to keep in mind that the flap doesn’t contribute any structural strength to the cornea. Therefore, if you have too thin of a cornea or too high of a correction, PRK is a lot safer. Some conventional wisdom also suggests ectasia is less likely with PRK in certain cases. For example, if someone has a slightly irregular corneal map, you might want to slant toward PRK, considering that PRK will help you avoid ectasia in some cases.
|Figure 1. This 22-year-old male, with a refraction of -2.50-4.40 D X 168, isn’t a candidate for LASIK because his central corneal thickness, at 490 µ, was too thin. The patient successfully underwent PRK, followed by treatment with mitomycin-C.|
“Can minute differences in the maps really suggest a risk of ectasia? It’s debatable, but I like to play it safe. You should be doing what you’d do if you were the patient. Taking away less tissue with PRK, possibly staying on slightly stronger legal ground, is also not a bad idea.”
Dr. Bond says he performs 500 to 1,000 refractive surgery procedures per year, including 15 to 35 percent that turn into PRKs. “I typically do PRK about 20 percent of the time,” he notes. “You have patients who can’t hold still, or a double-digit myope whose cornea isn’t overly thick. Sometimes, I have a little problem with a flap; after that, I might use PRK, in as many as one-third of my procedures. On the other hand, you’ll get a patient who has a very difficult time healing after surface ablation and experiences a lot of pain. An experience like that may push my PRK percentage back down. It’s like baseball. You’re only as good as your last time up at bat, and you’re always trying to figure out your best approach and learn as you go.”
Making sure patients fit the right profile for LASIK or PRK is also important, he adds. “Make them aware of the increased stability of refractive surgery without a flap (especially in the event of trauma),” he says. “I try to help them project into the future to determine if they just might end up doing something career- or lifestyle-wise that would not be good for a LASIK patient. Despite all of your counseling, though, you need to leave the decision to the patient. I’ve done LASIK on rodeo clowns that came to us as a group. That’s what they wanted, despite the risks that I reviewed with them.”
Dr. Bond notes that he only rarely considers implanting phakic intraocular lenses. “I’ve done them, yes, and I’ve had good luck doing them,” he recalls. “However, you raise the risk of more serious complications in these cases. With PRK, your complications are completely outside the eye. With LASIK, you could see issues involving the flap. If you put an ICL into a 22-year-old patient, however, you could cause a cataract or endophthalmitis or some other problem. You’ve moved up to your bigger-league complications, whether they’re common or not.”
Like Dr. Bond, many other surgeons prefer to err on the side of caution. As a surgeon who doesn’t focus primarily on refractive surgery, corneal specialist Brandon Ayres, MD, is one of these doctors.
“For any patient with a corneal thickness of 500 µm or less, even if the safety parameters for doing LASIK are met, I consider the cornea thinner than usual and I’ll do PRK,” says Dr. Ayres, co-director of the Cornea Fellowship at Wills and an instructor at Jefferson Medical College, Thomas Jefferson University in Philadelphia. “That’s purely my own rule. I don’t know if there’s any substance behind it. I just sleep better if I know I’m being safer for this patient.”
Penny A. Asbell, MD, FACS, MBA, FARVO, Barrett G. Haik Endowed Chair for Ophthalmology in the College of Medicine at the University of Tennessee Health Science Center, says many patients favor LASIK “because it provides a relatively quick visual recovery and because of the reduced discomfort initially. However, at six months, most of the reported results of LASIK and PRK are pretty equal in terms of vision. Deciding which type of surgery to perform has to do more with what you, as the surgeon, are comfortable doing. If you like LASIK and do a lot of LASIK, fine. However, LASIK as a technique poses more risk than surface ablation. If you don’t do a lot of refractive surgery because that’s not your primary focus in your practice, it’s probably less risky to do PRK, in terms of avoiding something major going wrong. You can go either way and, of course, you want to be able to do both because there are some patients who may require one or the other, depending on your findings and their preferences.”
|Figure 2. This 21-year-old female is a perfect candidate for LASIK, presenting with orthogonal, symmetric and regular astigmatism. With a refraction of -2.75-2.50 D X 169, her central corneal thickness was 594 µ and her pupil size was 5.7 mm.|
Dr. Chayet is a high-volume cataract and refractive surgeon who performs PRK if he sees any risks that could arise from lamellar incisional surgery, including LASIK and SMILE. This amounts to about 20 percent of his cases.
“For example, PRK may be indicated in patients with non-orthogonal asymmetric astigmatism,” he says. “This would be on a case-by-case basis, not always. I look for asymmetric thickness maps or abnormal epithelial maps. If you have the luxury of using some of the devices that provide biomechanical analysis, such as a Pentacam and keratoconus-screening software, you can detect these issues. Any time you have a thin cornea, you should be thinking about performing PRK on that patient. There are very few reports of ectasia following PRK.”
When new patients call his practice, inquiring about any form of refractive surgery (typically LASIK), Dr. Chayet’s staff reviews both PRK and LASIK with them. “There are no differences between these procedures as they’re presented to our patients,” he says. “They’re priced the same and equally effective. If patients want to have LASIK as a first choice, we will offer them LASIK if they’re good candidates. But if there’s anything that gives us concern about doing LASIK, then we’ll offer PRK as the first choice. The only consideration we have to keep in mind, which may encourage more patients to undergo LASIK if they’re good candidates, is the longer healing time and brief period of discomfort after PRK.”
Discomfort and Healing
Surgeons say they use varied approaches to minimize post-PRK discomfort, safeguard against infection and promote wound healing. Among the possibilities are bandage contact lenses, NSAIDs, topical antibiotics, topical steroids, ketorolac tromethamine ophthalmic solution, topical cyclosporine, preservative-free tears, oral steroids and oral analgesics (such as hydrocodone bitartrate/acetaminophen).
Dr. Chayet says he’s never used NSAIDs on the wound surface. “I don’t recommend using those agents,” he says. “We also don’t use anesthetics. Instead, we apply bandage contact lenses and topical steroids. We’ll also provide a non-opioid oral analgesic, such as oral ketorolac tromethamine (Toradol), and we don’t use alcohol on the surface. Patients have some discomfort for about two days. We tell them before the procedure what the postop period will be like, ensuring realistic expectations. Discomfort and longer healing time haven’t really been issues in more than 90 percent of our patients. Most don’t complain, and they’re satisfied with the results of their surgeries.”
Meanwhile, Dr. Chayet says he prevents corneal haze after performing PRK by treating his patients with the antimetabolite mitomycin-C for 20 seconds. “I only use it for ablations of more than 70 µm or in cases when I feel there’s a higher chance of post-PRK haze,” he says. He keeps the MMC away from the limbus to avoid toxicity and concentrates it on the central cornea. “I haven’t encountered any problems with this approach,” he adds.
Dr. Chayet acknowledges that PRK still has its drawbacks, even among the best candidates. “We can’t give PRK patients opioids in Mexico, so we’re limited in that way,” he says. “Ketorolac still isn’t perfect, and we’re always looking for other solutions. There’s interest in developing better topical analgesia, which hopefully we can use someday without interfering with re-epithelialization of the treated area of the cornea.”
None of the surgeons interviewed for this article discussed products made by companies with which they have a financial relationship.