Understanding pros, cons of the latest corneal refractive procedure

Chicago-On Sept. 13, 2016, the FDA announced that it was approving use of the VisuMax Femtosecond Laser (Carl Zeiss Meditec) for the small incision lenticule extraction (SMILE) procedure to treat myopia.

In a timely talk at Refractive Surgery 2016, Sunil Shah, MD, made a case for why refractive surgeons might want to consider this minimally-invasive corneal refractive procedure.

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Dr. Shah told attendees that SMILE is highly effective and has been associated with a very high patient satisfaction rate. In addition it appears to have a number of benefits compared with LASIK.

“Lower biomechanical impact may be the main advantage of SMILE. Furthermore, SMILE is associated with less dry eye, less induced aberrations, less subjective pain, less refractive regression, and it is less subject to influence from surgical environmental factors, such as hydration and exposure,” said Dr. Shah, Professor of Ophthalmology, Aston University, Birmingham, England.

Dr. Shah presented data to support some of these claims and he also acknowledged the limitations of the SMILE procedure.

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A review of refractive outcomes from nine SMILE studies published from 2011 through 2014 showed that the postoperative spherical equivalent was within 0.5 D of target in 84% of eyes overall.  While that predictability rate is not as good as with LASIK today, the outcome with SMILE seemed better in the more recent studies. And, in the FDA clinical trial leading to approval of SMILE for treatment of myopia, spherical equivalent correction at 12 months was within 0.5 D of attempted in 94% of eyes. Refractive results from the FDA trial also show excellent stability during the 12-month follow-up period, said Dr. Shah.

Discussing SMILE’s biomechanical benefit, Dr. Shah said it has been demonstrated using different instruments to measure biomechanical properties. The lower biomechanical impact of SMILE compared with LASIK is explained by the fact that SMILE leaves the anterior stroma, which is the strongest part, largely intact, save for the region of the small incision used for lenticule extraction.

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In addition, because the cornea is largely cut below the nerve plexus by SMILE whereas LASIK severs the sub-basal nerves, SMILE causes less dry eye than the flap-based procedure. Evidence supporting a difference between the two refractive surgeries is also available from a number of studies assessing a variety of parameters, including nerve density, corneal sensitivity, tear osmolarity, Schirmers test results, and patient use of ocular lubricants.

Fair balance

Fair balance

Dr. Shah was careful to note that SMILE is not problem free. Yet, its safety profile is good. A study by Ivarsen et al. [Ophthalmology. 2014;121:822-824] looking at the safety and complications of SMILE in more than 1500 procedures found the most common complication was trace haze (8%).

“Eyes can develop diffuse lamellar keratitis, and in this series there were four cases of interface inflammation, but it was relatively mild, and epithelial ingrowth at the edge of the incision is also possible,” Dr. Shah said.

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When it comes to disadvantages of SMILE, Dr. Shah suggested that the major drawback at the moment is cost. In addition, patients should expect slightly slower visual recovery compared with LASIK, and they need to know there is a slightly greater risk of loss of corrected visual acuity

“Like with any other new procedure, there is also a learning curve for SMILE and slightly different complications. In addition, it is difficult to control astigmatism with SMILE at present, and we are still waiting for approval to treat hyperopia and for customization,” Dr. Shah concluded.