Surface ablation techniques register growth trend in Europe

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Paolo Vinciguerra, MD, said PRK is well-suited for the entire range of refractive errors treatable by laser. Image: Vinciguerra P

The advent of LASIK relegated surface ablation to a niche procedure for some years, but recent times have witnessed a slow but steady return of surface ablation in its many variations: PRK, LASEK, epi-LASIK and epi-LASEK.

“In 1991, it seemed as if surface ablation had received its death sentence. Twenty years later, we can say that not only it is still alive and well, but it is also on the increase,” Paolo Vinciguerra, MD, head of ophthalmology at the Humanitas Clinic in Milan, said.

“Speaking with colleagues from all over the world, I have the impression that surface techniques are performed more than in the past. New lasers that produce smoother surfaces and the use of mitomycin C have minimized the problem of haze, and surgeons who only did LASIK now perform surface ablation in a certain number of cases,” Massimo Camellin, MD, OSN Europe Edition Editorial Board Member, said. Dr. Camellin developed LASEK in 1998, and in his private practice in Rovigo, Italy, he treats about 500 patients a year with the procedure.

Italy in particular has maintained a strong tradition of surface-based refractive surgery, but in all European countries, this approach has a fairly large group of advocates.

“There are a relatively small number of practices where surface ablation represents the vast majority of laser procedures, and there are practices where LASIK is still the majority, but there is a positive trend toward surface ablation, up to 20% of the total volume of refractive surgery,” Daniel Epstein, MD, PhD, a professor of ophthalmology in Bern, Switzerland, said. “This is happening in Europe, but also in some practices in the U.S. and in other countries like Israel, where PRK is enjoying great popularity at the moment.”

Francesc Duch, MD, director of refractive surgery at the Institut Català de Retina, Barcelona, uses PRK in 30% to 40% of his cases.

“We organize 10 patient sessions, and at every session we have at least three to four cases for surface ablation. If you want to be a comprehensive refractive surgeon, you should include all techniques, because there are specific indications for each one of them. This is what I teach to my residents,” he said.

“The scenario is constantly changing because the technology evolves,” Michiel Luger, MD, medical director of VisionClinics, Utrecht, the Netherlands, said.

“We have done refractive surgery for about 12 years. At first, we mainly did LASIK; then we changed to around 50% to 70% PRK, and when the femtosecond laser emerged, we switched back to LASIK with thin flap. We do now 70% LASIK and 30% PRK. If the patient is suitable for both procedures and motivated to do LASIK, I do LASIK, but there are a lot of circumstance in which PRK is preferable,” he said.

Indications, range of correction

The main indication for surface ablation is a thin cornea, below 500 µm or even 480 µm for some surgeons.

With other irregularities, scars or little leukomas due to corneal conditions such as adenovirus keratitis, surface ablation is also a better approach, according to Dr. Duch.

Patients in professions with a heightened risk of eye trauma, such as police officers or firefighters, or those involved in activities that could result in being hit in the eye, such as basketball, tennis or golf, should never be operated with LASIK, according to all the surgeons who were interviewed.

Both Dr. Epstein and Dr. Luger said that it is important to listen to what the patient wants. Patients today are well-informed, and many have specific requests.

“There are people who definitely want LASIK because they need to go back to work as soon as possible. Under this specific request, I might do LASIK if there are the conditions for it, ie, low refractive error, adequate thickness and a regular surface,” Dr. Vinciguerra said.

Surgeons’ opinions vary regarding the range and type of refractive error treated with surface procedures as opposed to LASIK.

Francesc Duch

Dr. Duch reserves PRK strictly for low myopia, as he does not like to use mitomycin C on virgin corneas. The average eye he treats is –3 D, and he said he recalls only a few exceptions up to –5 D. Astigmatism higher than 2 D and hyperopia are excluded.

“In both [of] these cases the re-epithelialization process is different, and we’d have too much haze. I treat high astigmatism, hyperopia and the combination of the two, up to 5 D to 6 D, with LASIK. I use LASIK also for higher myopia up to –7 D, then I switch to phakic lenses,” he said.

Dr. Vinciguerra, on the contrary, said that LASIK should only be considered, if ever, for low myopia cases, while PRK is well-suited for the whole range of refractive error that laser can treat.

“In the early days, LASIK promised to be a good technique for very high myopic treatments, up to and above 10 D to 12 D. But optical zones had to be small enough to be contained within the diameter of the flap, and the resulting optical quality was extremely poor. Later, the first reports on post-LASIK ectasia started coming out,” he said.

As a rule, Dr. Epstein uses PRK for up to –7 D or –8 D of spherical equivalent, depending on corneal thickness.

“I might go above those limits from time to time with PRK, but I would never do it with LASIK,” he said.

Dr. Luger treats the same range of refractive error, between –0.75 D and –10 D, with either PRK or LASIK. He never treats hyperopia with PRK.

Massimo Camellin

Dr. Camellin uses surface ablation, specifically LASEK or epi-LASEK, which is a form of epi-LASIK with the use of alcohol, for all his cases.

“With the use of mitomycin C 0.02%, the problem of haze is avoided entirely. I correct up to –10 D of myopia and also hyperopia up to +4 D and astigmatism up to 6 D. No more than this, to preserve visual quality,” he said.

In his view, surface treatments can be used for higher corrections than LASIK, not only in consideration of the risk of ectasia, but also because larger optical zones can be ablated and because, with no flap, there is more tissue depth available.

Advantages of surface treatments

An advantage of surface procedures as compared with LASIK is the increased safety in relation to corneal biomechanics and complications.

“They have no effects on corneal biomechanics, and we can therefore treat higher refractive errors with larger optical zones,” Dr. Camellin said.

First described by Seiler and colleagues in 1998 and later reported by several other authors, surgically induced ectasia has cast a shadow over the reputation of LASIK.

“After so many years and all the precautions we have adopted to avoid it, ectasia still remains an issue.” Dr. Epstein said. “The increased safety of femtosecond-laser LASIK, with or without [a] thin flap, has yet to be established. Ectasia might develop 5 to 7 years after the procedure, and though the femtosecond laser has been around for so long, it has had a limited amount of users. It will be years before we have a sufficient number of procedures to draw significant conclusions.”

According to Dr. Camellin, a flap, whether it is created with a femtosecond laser or a microkeratome and despite how thin it is, inevitably alters corneal biomechanics.

“The point is that you always cut the Bowman’s, which is like an elastic bandage that holds the cornea together. By doing this, you weaken the cornea,” he said.

With surface ablation, only a small 5- to 6-mm area of Bowman’s membrane is affected centrally; then the treatment goes more superficial, toward the periphery. But the LASIK flap is a large dissection of Bowman’s membrane that is, in his opinion, the cause of ectasia.

Dr. Duch said the many papers comparing the effects of surface ablation vs. lamellar techniques with thin flaps confirm that there is a difference.

“A cut remains a cut, even with femto technology,” he said.

Another advantage of surface techniques is that all flap-related complications, such as folds, interface inflammation and displacement, are avoided.

“Also, femtosecond-created flaps have risks. Suction loss, tissue bridges, gas breakthrough and other complications may occur. Thin flaps are no better. They more easily have folds on top of all the other complications of thicker flaps,” Dr. Camellin said. “We can handle these problems, of course, but they are better avoided. Surface ablation is easier and safer.”

Quality of vision, according to some surgeons, is also better after surface treatment. In several studies Dr. Duch performed, he found that in the low myopia range that he treats, contrast sensitivity and wavefront results with PRK were better than with LASIK.

In addition, over a period of 1 or 2 years, PRK results continue to improve because of the long-term process of surface remodeling. The same does not happen with LASIK.

“Patients treated with LASIK in one eye and PRK in the other eye definitely see better with the LASIK eye in the short term, but after 1 or 2 years, they report significantly better vision with the PRK eye,” Dr. Vinciguerra said.

Custom approach and smoothing

To optimize visual results, Dr. Vinciguerra uses a topography-based customized approach with PRK.

“I don’t believe in total wavefront-guided. Even when the initial enthusiasm made a lot of people try it, I was a voice outside the mainstream. The internal wavefront always changes. It changes with age but also, and constantly, with accommodation. You cannot design your ablation pattern on such an unstable entity. In addition, if you try to compensate the internal aberrations, you inevitably generate a very irregular profile with irregular tear-film distribution and, in the long term, tissue growing to ‘fill in the gaps.’ The end result will be very different from what you had expected,” he said.

The cornea, on the other hand, is stable and has a stable wavefront. Therefore, cornea-based topography-guided treatments are more effective.

“I’ve never had a patient coming back to complain because of residual internal aberrations, but many patients with an apparently good total wavefront and a bad cornea,” he said.

In addition, the resolution of wavefront systems is lower than the resolution of topographers, and the accuracy of treatment is not equal.

Customized treatments were attempted with LASIK as well, but it was soon clear that only PRK could sustain this approach.

“You program your ablation based on the cornea, but when you cut the flap, the cornea is no longer the same,” Dr. Vinciguerra said.

At the end of PRK surgeries, Dr. Vinciguerra adds a few microns of smoothing with masking fluid. This eliminates the risk of haze and regression and makes PRK even safer, he explained.

“It’s an off-label procedure but widely used in Italy and has certainly contributed to the popularity of PRK here because results are significantly better than without it. In the U.S., it is not [U.S. Food and Drug Administration] approved and not used at all, and this has given another advantage to LASIK,” he said.

Drawbacks of surface ablation

Drawbacks of surface treatments are some degree of postoperative pain, the discomfort of wearing a contact lens for a few days and a longer visual rehabilitation as compared with LASIK.

Considerable reduction of pain is obtained with LASEK and its variations, if a correct postoperative management protocol is applied, according to Dr. Camellin. One drop of antihistamine just after surgery, together with preservative-free NSAIDs and corticosteroids, should be applied.

“Antihistamines are mediators of pain, and it is important to block out pain right at its onset,” he said.

Pressure on the flap and a contact lens should be applied with the Johnston applanator (Rhein Medical) to squeeze out the fluid and make the flap adhere firmly to the stromal surface.

“This helps keeping the flap, which is mandatory in the first 24 hours to avoid pain, and is what makes LASEK different from PRK,” Dr. Camellin said.

Of his patients, 90% report no pain 1 day after surgery, and 10% have complaints that range from a mild burning sensation to pain. If a higher rate of pain is reported in some papers, this is mostly because recommendations are not followed, he said.

“We have learned how to manage pain, but still the patient cannot go back to work immediately,” Dr. Epstein said. “All variations of PRK are the same in this respect: They all need a few days to heal and a few weeks to 1 month to achieve full visual recovery.”

“The chance of experiencing some pain for a few days and 1 week of relative inability to work seem a small price to pay for the high safety profile of surface techniques. A minor inconvenience compared to the short- and long-term hazards of LASIK,” Dr. Camellin said. “But LASIK has won the largest share on the market based on two of the most appealing concepts in our society: no pain and instant gratification. Selling these ideas is a tremendous marketing strategy.”

“Add to this the pressure to be super-productive, which is so strong in the U.S., and you’ll understand why surface procedures have never taken root there. In Europe, that is, a less production-oriented society, taking a sick leave is less of an issue,” he said.

According to the surgeons, however, people are beginning to change their priorities. A small but increasing number of patients are prepared to pay the price of initial discomfort in view of long-term safety.

“Of course you need to speak clearly to them and be objective about the pros and cons of the two procedures,” Dr. Epstein said.

“You also must be prepared to pay the price of a longer follow-up and a more demanding psychological approach. There might be discomfort with the contact lens, there might be postoperative pain, and your patients will need assistance,” Dr. Camellin said.

Transepithelial PRK approach

A newly developed technique with one specific laser has taken PRK forward in minimizing pain and shortening the healing process, according to Dr. Luger.

Michiel Luger

It is a no-touch, all-laser transepithelial approach in which the epithelium is removed by the laser after the refractive correction has been performed. An algorithm calculates the correction in the corneal stroma minus the epithelium, and it is known exactly how much of the epithelium will be removed. The laser is accurate and minimally traumatic, which leads to a faster healing process. Dr. Luger noted that the contact lens, which was previously removed at 4 days, is now removed at 2 to 3 days.

“Postoperative pain is also less than in conventional PRK. Fewer patients complain, and those who do seem to suffer less and for a shorter time,” he said. “It’s a quick, very precise, very effective procedure. Not many surgeons use it because there’s only one machine doing it, but in our practice the amount of PRK has increased a lot since we have introduced it. We treat around 6,000 patients per year in this practice, and around 1,000 are PRK with transepithelial approach.”

The future

It is difficult to say in what proportion surface and lamellar procedures will be used in the future, but they are likely to continue to coexist.

“There are new developments in the surface approach, such as transepithelial PRK, but there are new developments in LASIK too, with the femtosecond laser treating the cornea intrastromally,” Dr. Luger said.

Dr. Camellin said new techniques show possibilities for the future.

“The intrastromal approach is promising, because we’ll have a LASIK procedure where there is no flap and the Bowman’s is not cut. All complications will be avoided,” he said.

Dr. Epstein said that, in the future, it is possible that a strictly surface ablation or lamellar approach may not exist. Instead, a whole new idea may take shape.

“What we are aiming at is a procedure with a very small opening or no opening, where the ablation is done inside the eye without damaging the outside nor weakening the biomechanical structure. This new approach will take us beyond the dichotomy of surface and lamellar procedures and will be something totally different, which leaves PRK and LASIK behind,” Dr. Epstein said. – by Michela Cimberle

Would you consider PRK as a re-treatment after LASIK?

References:

• Camellin M. Laser epithelial keratomileusis for myopia. J Refract Surg. 2003;19(6):666-670.
• Camellin M. Laser epithelial keratomileusis with mitomycin C: indications and limits. J Refract Surg. 2004;20(5 Suppl):S693-698.
• Camellin M. What about LASEK? J Refract Surg. 2008;24(5):462.
• Camellin M, Wyler D. Epi-LASIK versus epi-LASEK. J Refract Surg. 2008;24(1):S57-63.
• Epstein D. Refractive surgery. Ther Umsch. 2009;66(3):207-210.
• Neira-Zalentein W, Moilanen JA, Tuisku IS, Holopainen JM, Tervo TM. Photorefractive keratectomy retreatment after LASIK. J Refract Surg. 2008;24(7):710-712.
• Seiler T, Koufala K, Richter G. Iatrogenic keratectasia after laser in situ keratomileusis. J Refract Surg. 1998;14(3):312-317.
• Vinciguerra P, Albè E, Camesasca FI, Trazza S, Epstein D. Wavefront- versus topography-guided customized ablations with the NIDEK EC-5000 CX II in surface ablation treatment: refractive and aberrometric outcomes. J Refract Surg. 2007;23(9 Suppl):S1029-1036.
• Vinciguerra P, Camesasca FI, Bains HS, Trazza S, Albè E. Photorefractive keratectomy for primary myopia using NIDEK topography-guided customized aspheric transition zone. J Refract Surg. 2009;25(1 Suppl):S89-92.
• Vinciguerra P, Randazzo A, Albè E, Epstein D. Tangential topography corneal map to diagnose laser treatment decentration. J Refract Surg. 2007;23(9 Suppl):S1057-1064.

• Massimo Camellin, MD, can be reached at SEKAL, Via Dunant 10, 45100 Rovigo, Italy; phone/fax: +39-0425-411357; email: cammas@tin.it.
• Francesc Duch, MD, can be reached at Institut Català de Retina, Pau Alcover, 67, 08017 Barcelona, Spain; +34-93-254-79-20; fax: +34-93-418-96-02; email: duch@icrcat.com.
• Daniel Epstein, MD, PhD, can be reached at Bernese Eye Research Institute, Switzerland; +41-0041-31-3114822; email: epstein.dan9@gmail.com.
• Michiel Luger, MD, can be reached at VisionClinics, Postbus 85337, 3584 AA Utrecht, The Netherlands; +31-30-7114804; fax: +31-30-7114819; email: luger@visionclinics.nl.
• Paolo Vinciguerra, MD, can be reached at Istituto Clinico Humanitas, Via Alessandro Manzoni, 56, 20089 Rozzano Milano, Italy; +39-02-82246205/02; fax: +39-02-82242554; email: paolo.vinciguerra@humanitas.it.
• Disclosures: The sources have no relevant financial disclosures.