Femtosecond lasers minimize role of surface ablation in refractive surgery

With the growing safety and efficacy of LASIK, surgeons may be less likely to choose surface ablation.

Despite the resurgence of surface ablation observed several years ago, the procedure has been losing popularity among refractive surgeons due to recent advancements in femtosecond laser technology.

Early techniques in surface ablation were often painful for patients, but improvements in preventing pain with topical nonsteroidal anti-inflammatory drugs, topical dilute anesthetics and oral medications, as well as a reduction in haze rates, allowed surgeons to perform a more comfortable and ultimately more effective procedure.

With the improvements in patient experience and visual outcomes and the reduction in complications, the volume of surface ablation procedures began to steadily increase during the last decade. However, the tide has turned more recently with innovations in femtosecond laser platforms that have improved the safety and accuracy of LASIK. The percentage of surface ablation cases has been dropping while the percentage of femtosecond LASIK procedures has been rising.

Choosing between surface ablation and LASIK

William B. Trattler

According to William B. Trattler, MD, OSN SuperSite Board Member, surface ablation is still a valuable procedure that continues to evolve with improvements in postoperative care.

“Surface ablation is an excellent procedure,” he told Ocular Surgery News. “Our patients achieve very good visual results, and the comfort level has improved over time with our better understanding of how to keep patients more comfortable postoperatively.”

Surface ablation — or more specifically, PRK — uses an excimer laser to remove a small amount of tissue from the cornea. The resulting corneal structure is often less altered than it would be with a microkeratome, which many surgeons still use for LASIK.

However, Dr. Trattler said femtosecond lasers have increased LASIK safety. He said he prefers to perform femtosecond LASIK over surface ablation if patients are eligible to undergo either procedure.

Even though LASIK and surface ablation offer similar visual results at 3 months, Dr. Trattler said patients who undergo femtosecond-flap LASIK are not only more comfortable after surgery but have a more rapid visual recovery and can typically drive a car the day after surgery.

Christopher L. Blanton, MD, agreed that the current trend in refractive surgery is focused on LASIK because of the emergence of femtosecond flap creation.

“The ability to create thinner flaps has decreased the fear of creating ectasia in our patients,” he said, recalling lawsuits several years ago that caused surgeons to worry about causing iatrogenic keratectasia in patients who undergo LASIK.

Because LASIK yields faster visual recovery times and less discomfort, Dr. Blanton said he needs compelling reasons to convert to surface ablation. One factor he takes into consideration is a patient’s lifestyle, including occupation or hobbies.

In order to avoid flap complications associated with postoperative trauma, he said he recommends surface ablation to patients who play contact sports or are involved in the military or law enforcement.

Dr. Blanton added that surface ablation is a safer option for patients with prior LASIK because of the chance for epithelial ingrowth, as well as for patients with questionable topography. Because it is difficult to define what is abnormal in topographic maps, if there is any question, Dr. Blanton said, most surgeons will choose surface ablation with the expectation that it will be less likely to cause ectasia.

According to Dr. Trattler, peer-reviewed literature has shown that PRK is an appropriate option for patients with mild forme fruste keratoconus, as long as the patient’s vision is “correctable to 20/20 and the ablation is not too deep,” he said.

For patients with more advanced forme fruste keratoconus, Dr. Trattler said he suggests collagen cross-linking first, followed by surface ablation 6 months to 1 year later. The same treatment plan can be followed for patients with suspicious topographies, he added.

Debate over thin corneas

With the use of femtosecond lasers on the rise, the relevance of central corneal thickness has become a controversial topic in refractive surgery. Surgeons disagree about whether corneal thickness increases the risk of ectasia after LASIK in cases with normal topography.

Dr. Trattler is inclined to evaluate each patient individually to determine whether surface ablation is a safer alternative to LASIK. He said in general, patients with thin corneas and normal topographies are appropriate candidates for LASIK, as long as they are left with a sufficient residual bed. Multiple peer-reviewed articles have demonstrated that LASIK in these eyes is safe and effective, Dr. Trattler added.

According to Dr. Blanton, many surgeons deem abnormal any cornea less than 500 µm thick. However, he said he prefers to follow guidelines from a study published in the Journal of Refractive Surgery based on results from an Optical Express database suggesting that 480 µm is the thinnest cornea that should undergo LASIK, as long as the rest of the eye is considered healthy.

Advanced techniques increase comfort

Christopher L. Blanton

The difference between the postoperative complications of surface ablation and LASIK are under investigation, but Dr. Blanton said neither procedure appears to have an advantage over the other in terms of vision quality or side effects.

However, advanced surface ablation techniques such as mitomycin C, more comfortable bandage contact lenses and newer medications have all resulted in improved visual outcomes and increased comfort level for patients undergoing the procedure.

“Surface ablation has reached a place where we can offer a reasonably comfortable, fairly rapid recovery of vision in our patients … but it still remains inferior to LASIK,” he said.

Dr. Blanton noted, however, that surface ablation has a theoretical advantage for dry eye patients because it is less invasive than LASIK in terms of depth, and therefore creates less disruption of the corneal nerve plexus.

Conversely, Dr. Trattler said that based on two studies, the risk for dry eye is identical in both PRK and thin-flap LASIK with a femtosecond laser, and a proactive approach can be used to prevent the development of dry eye with both PRK and LASIK. His treatment protocol includes punctal plugs, Restasis (cyclosporine A, Allergan) and additional dry eye treatments administered preoperatively and postoperatively.

Future role of surface ablation

Although femtosecond lasers are making LASIK the preferred choice among many refractive surgeons, the procedure has been the subject of controversy.

In response to growing concern about the long-term safety of LASIK, the U.S. Food and Drug Administration has partnered with the National Eye Institute and the U.S. Department of Defense to evaluate patient quality of life following LASIK. The three-part study, launched in 2009, has the potential to validate the perceived safety and efficacy of LASIK. Dr. Trattler expects that the results will confirm the procedure’s safety and efficacy rather than steer refractive surgeons back to surface ablation.

“If anything, I think it will make patients feel more comfortable to undergo LASIK,” he said.

Dr. Blanton is similarly optimistic about LASIK’s fate, although he predicts future clinical innovations could alter refractive surgery trends once again.

“LASIK is likely to remain the dominant procedure unless the scientific community develops a method for rapidly replacing the corneal surface, or we go intrastromal — leaving behind flap complications and surface healing issues,” he said. – by Courtney Preston

References:

• Brown MC. An evidence-based approach to patient selection for laser vision correction. J Refract Surg. 2009;25:S661-S667.
• Caster AI, Friess DW, Potvin RJ. Absence of keratectasia after LASIK in eyes with preoperative central corneal thickness of 450 to 500 microns. J Refract Surg. 2007;23(8):782-788.
• He TG, Shi XR. [Clinical study of ultrathin flap LASIK and LASEK for the treatment of high myopia with thin cornea]. Zhonghua Yan Ke Za Zhi. 2006;42(6):517-521.
• Kremer I, Bahar I, Hirsh A, Levinger S. Clinical outcome of wavefront-guided laser in situ keratomileusis in eyes with moderate to high myopia with thin corneas. J Cataract Refract Surgery. 2005;31(7):1366-1371.
• Kymionis GD, Bouzoukis D, Diakonis V, et al. Long-term results of thin corneas after refractive laser surgery. Am J Ophthalmol. 2007;144(2):181-185.
• U.S. Food and Drug Administration. FDA provides update on LASIK quality of life collaboration project status. http://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm230139.htm. Accessed November 9, 2010.

• Christopher L. Blanton, MD, can be reached at Inland Eye Institute, 3257 E. Guasti Road, Suite 210, Ontario, CA 91761; phone: 909-937-9230 or 800-570-5273; e-mail: blanton007@aol.com.
• William B. Trattler, MD, can be reached at the Center for Excellence in Eye Care, 8940 N. Kendall Drive, Suite 400-E, Miami, FL 33176; 305-598-2020; fax: 305-274-0426; e-mail: wtrattler@gmail.com.
• Disclosures: Dr. Blanton is a paid consultant to Abbott Medical Optics and Allergan. Dr. Trattler is a consultant, is on the speaker’s bureau, and/or receives research support from Abbott Medical Optics, Bausch + Lomb, WaveTec, Lenstec and LensAR.

Surface ablation has certainly been around for a long time, and I think there is a role for it in certain cases. The role of surface ablation can be several-fold. First, it can be used in patients who would rather have surface ablation performed. Second, it can be based on job or career, because certain careers lend themselves better to one procedure, or require one procedure over the other. For example, certain aspects of the military and certain professions that could be more affected by trauma may be better candidates for surface ablation. And, surface ablation may be used in people with larger degrees of near-sightedness, where depth of the cornea is an issue. I think many people are seeing resurgence in this third instance. With a microkeratome, surgeons are cutting thicker flaps, which limits the amount of treatment that can be done. Today, we are trying to leave more residual bed tissue than we did 5 or 10 years ago to prevent corneal ectasia. For those of us who use IntraLase (Abbott Medical Optics), we can very predictably create thin flaps so we are not as likely to be performing surface ablation in those instances. In other words, iLASIK permits surgeons to operate on thinner corneas and still preserve robust residual beds due to the creation of thinner, reproducible corneal flaps.

Lastly, I think studies have shown very clearly that, assuming all the rest of the corneal architecture, thickness and shape of the front and back surface of the cornea is normal, having a thin cornea (500 µm or 490 µm) does not necessarily rule out LASIK. There are certain surgeons who feel that LASIK is appropriate, even on a thin cornea, provided the ablation does not go deeper than 300 µm or 250 µm. And there are other surgeons who just feel surface ablation is better for thinner corneas — and the results with surface ablation in combination with mitomycin C have been very successful. These days, patients and surgeons have choices and options.

– Kerry D. Solomon, MD
OSN Refractive Surgery Board Member
Disclosure: Dr. Solomon is a consultant and/or receives financial support from Alcon, Allergan, Bausch + Lomb, AMO, Advanced Vision Research, QLT, Inspire, Wavetec, Aquesys and Glaukos.