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Over the years, LASIK has garnered some unfortunate press and a negative image—undeservedly so, in my opinion—despite advances in the past 25 years that have improved outcomes and made the surgery safer. It is worthwhile to keep in mind, however, that the LASIK market originally grew because of patients’ demand for the procedure. Patients’ preferences will continue to drive the future of refractive surgery. Indeed, refractive surgery is still very much desired by many patients, and they might welcome new options that offer similarly excellent results.
In the interest of giving patients more options for refractive correction, the recent FDA approval of small-incision lenticule extraction (SMILE) for myopia is a welcome addition to the refractive surgery repertoire. In this technique the VisuMax femtosecond laser (Carl Zeiss Meditec) is used to cut a small lenticule that is then extracted. Investigations to date suggest that SMILE provides safety and efficacy outcomes at least comparable to those of LASIK. It uses a different approach to modifying the optical system, however, which may confer benefits including potentially faster healing, if not faster visual recovery.
The laser SMILE procedure is performed in four stages:
• the underside of the lenticule is cut
• the sides of the lenticule are cut
• the upper border of the lenticule is cut
• an opening incision is created
The patient is then moved to the microscope, where the surgeon removes the lenticule through the opening incision.
In a phase 3 trial, 327 of 328 eyes treated with SMILE achieved 20/40 or better vision 6 months postoperatively, and 88% of eyes achieved 20/20 or better. Issued related to loss of suction, and complications such as dry eye and moderate to severe glare and halo, were seen with rates comparable to those reported after LASIK.1
As one of the investigators in that trial, I had the opportunity to learn about this procedure and what advantages it may offer in certain patients, and I share some of these insights in this article.
Patient selection is important for the success of any surgery. As SMILE is rolled out commercially, we will undoubtedly learn more about the nuances of who may benefit from it the most. For now, we know that SMILE has the potential to fix myopia and astigmatism, although it is now approved only for correction of myopia between -1.00 and -8.00 D.
(I was the medical monitor of a trial looking at SMILE for the treatment of myopic astigmatism; that study has been completed, and results have been submitted to the FDA. I am not able to share specific data, but I can say that the outcomes were very promising.)
To date, close to 600,000 SMILE procedures have been performed worldwide, with outcomes equal to and in some cases superior to those of LASIK. Any patient who would be a candidate for myopic LASIK would likely be equally suitable for SMILE. However, the features of SMILE and how it is performed may make it a more desirable option for some patients.
Compared with LASIK, fewer corneal nerves are truncated during the SMILE procedure, so there appears to be a theoretical reduction of risk postoperative dry eye. Equally, those with preoperative dry eye may experience easier healing after SMILE than after LASIK.
RISK FOR ECTASIA
Whereas LASIK procedures require creation of a corneal flap around 270° for access the stromal bed, in SMILE the entrance incision is 45° to 60.° Moreover, more of Descemet membrane is preserved in SMILE relative to LASIK, leaving more of this strongest part of the cornea intact. As refractive surgeons are well aware, with proper patient selection LASIK does not cause ectasia, but in a cornea prone to ectatic changes it can hasten its onset. Because less tissue is disturbed in SMILE, the procedure appears to offer better postoperative corneal biomechanical integrity than LASIK.
VERY HIGH MYOPIA
SMILE is not a dose-dependent procedure. That is to say, with LASIK, the higher the refractive error treated, the more laser stromal ablation must be applied, leading to longer procedures with more energy application, in which the flap and cornea are exposed longer to drying conditions.
With SMILE, on the other hand, anterior and posterior laser cuts are made, and the only variable is how far apart to place them; the same amount of energy is applied to low and high myopes alike, in the same span of time. As a result, although a typical scattergram of LASIK outcomes tends to get a greater spread of results among very long eyes, a scattergram of similar patients with SMILE would demonstrate tighter clustering around the mean, indicating more consistent outcomes.
PATIENT PREFERENCE AND THE FUTURE
Although SMILE may be preferred over LASIK for clinical reasons in certain cases, patient preference will most often be the determining factor in which option patients select. If the experiences in Europe and Asia with SMILE are an indication, the desire to avoid a flap-based procedure will be important to some patients; others will be attracted by the novelty of SMILE, the latest refractive surgery offering; still others may be wary because of LASIK’s previous bad press and eager to try something new and different. When LASIK was introduced 25 years ago, it offered outcomes similar to those of PRK, but it became the favored option for correcting vision due to popular demand. In the ensuing time, advances such as eye tracking capabilities, femtosecond laser flap creation, and wavefront-guided ablation have greatly improved the safety and efficacy of LASIK. In most cases, SMILE will yield outcomes comparable to those with the most advanced LASIK techniques and technologies, so it will be interesting to see how the court of popular demand rules in terms of patient preference.
In the near term, a review by the FDA of clinical data on SMILE in myopic astigmatism is anticipated, and ongoing research is exploring SMILE techniques for correction of hyperopia. It is hoped that these developments will complement the success of SMILE for myopia and add to our ability to give patients the final vision they want. These advances provide good options for patients today, and they establish a platform that can be further improved to offer even better options in the future.
1. FDA approves VisuMax Femtosecond Laser to surgically treat nearsightedness [press release]. US Food and Drug Administration. September 13, 2016. http://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm520560.htm. Accessed January 19, 2017.
Stephen G. Slade, MD
• Private practice at Slade and Baker Vision in Houston, Texas
• (713) 626- 5544; firstname.lastname@example.org