Refractive surgeons look to SMILE into the new year

The newly approved refractive procedure is poised to enter the US market.

Issue: February 10, 2017

ByMitchell A. Jackson, MD

Premium surgeons are embarking upon the new year with new refractive surgery procedures recently approved by the FDA, such as the Raindrop corneal inlay from ReVision Optics. Even more exciting is the FDA approval of the VisuMax small incision lenticule extraction procedure from Carl Zeiss Meditec for reduction or elimination of myopia from –1 D to –8 D, with 0.5 D cylinder or less and manifest refraction spherical equivalent of –8.25 D in the eye to be treated in patients who are 22 years of age or older with documentation of stable manifest refraction over the past year.

With more than 51 million LASIK procedures performed worldwide, SMILE brings a new era of sophistication to myopia correction in the U.S. in what we can call microincisional refractive surgery (MIRS), no different from MICS and MIGS in cataract and glaucoma surgery, respectively. SMILE has already been established in global markets such as Europe, China, Australia, Canada and India.

Pivotal FDA study results

The U.S. FDA trial was composed of 336 eyes in a prospective, multicenter, open-label, single-arm study at five investigational sites with unilateral treatment and a minimum of 12 months of follow-up. Central corneal thickness had to be at least 500 µm. Endpoint data showed excellent uncorrected visual acuity results, such that 88% were 20/20 or better and 65% were 20/16 or better at 12 months. Refractive stability postoperatively was excellent as well, as 93.9% were within 0.5 D of target and 99.6% were within 1 D at the 12-month data point. At 12 months, 74% of patients ended up with better UCVA postoperatively than best corrected visual acuity preoperatively. Only five eyes of the 336 eyes treated had intraoperative adverse events: one cap perforation, two difficult lenticule removals with tissue damage and two cases of retained tissue with lenticule removal. Overall, primary efficacy endpoints and safety data were obtained to grant FDA approval in September 2016.

Commercial U.S. launch

As Zeiss launches SMILE in the U.S. market, there are a few differences in the approval parameters here compared with internationally. The optical zone can be 6 mm or 6.5 mm in the U.S. but can go to 7 mm internationally, and the cap is always 1 mm larger than the intended optical zone treatment. Treatment depth is locked at 120 µm in the U.S. but is adjustable internationally. Some surgeons have stated that SMILE can be more difficult in lower myopia because of a thinner lenticule, but Dan Reinstein has published that by increasing lenticule thickness by using a larger optical zone and a minimum lenticule thickness of 20 µm to 25 µm instead of the standard 10 µm, this issue can be easily avoided.

SMILE advantages over LASIK

The “flapless” nature of this MIRS type of correction for myopia has some key advantages over LASIK in terms of less postoperative dry eye side effects and potentially less biomechanical weakening effect on the cornea, potentially reducing the risk of corneal ectasia postoperatively. LASIK-induced neurotrophic epitheliopathy, first described by Steve Wilson, is one of the main complications suffered by patients postoperatively, and the nerve plexus that is severed in LASIK is for the most part preserved with SMILE, and as a result corneal sensitivity recovers almost twice as fast with SMILE (3 to 6 months) compared with LASIK (6 to 12 months). With SMILE the stronger anterior stroma portion of the cornea is uncut, giving a potential biomechanical advantage for this procedure and thus allowing larger optical zone treatment sizes if needed without any additional weakening risk to the cornea.

SMILE limitations

The main limitation for U.S. surgeons will be the inability to treat spherocylinder corrections, which are typically present in the more moderate to high myopic approved treatments for this procedure. U.S. surgeons will also be limited to a fixed incision size to remove the lenticule compared with the more flexibility allowed internationally, but by having a microincision, SMILE has essentially transformed the correction of myopia to a minimally invasive procedure.

In the end, premium surgeons should be happy to SMILE as we move into this new year with advances in presbyopia and now myopia correction, with faster healing and lower risk with similar visual outcomes when compared with the standard we know as LASIK.

References:
Reinstein DZ, et al. J Refract Surg. 2014;doi:10.3928/1081597X-20141113-07.
Reinstein DZ, et al. J Cataract Refract Surg. 2015;doi:10.1016/j.jcrs.2014.12.055.
Wilson SE, et al. Am J Ophthalmol. 2001;doi:10.1016/S0002-9394(01)00995-3.

For more information:
Mitchell A. Jackson, MD, can be reached at Jacksoneye, 300 N. Milwaukee Ave., Suite L, Lake Villa, IL 60046; email: mjlaserdoc@msn.com.

Disclosure: Jackson reports he is a consultant for Carl Zeiss Meditec and ReVision Optics.