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SMall-Incision Lenticular Extraction for the treatment of myopia requires new surgical skills with a manageable learning curve.
Take-home message: SMall-Incision Lenticular Extraction for the treatment of myopia requires new surgical skills with a manageable learning curve.
By Cheryl Guttman Krader; Reviewed by John F. Doane, MD
Leawood, KS-SMall-Incision Lenticular Extraction (SMILE) for the correction of myopia provides outcomes that are at least as good as LASIK, and it has many advantages to offer patients and surgeons, John F. Doane, MD.
However, refractive surgeons interested in adding SMILE to their practice must be prepared to develop new skills.
“SMILE has a learning curve, but it is a learnable, straightforward procedure delivering refractive results that are equivalent to LASIK when treating low myopia and more predictable for higher myopia,” said Dr. Doane, refractive surgeon, Discover Vision Centers, Leawood, KS, and on the clinical faculty, Department of Ophthalmology, Kansas University Medical Center, Kansas City.
“Moreover, SMILE avoids flap-related risks, affords better corneal structural integrity compared with LASIK, and it can cut the capital expense in half for surgeons new to laser refractive surgery because the procedure is done with just a single laser,” he said.
However, cerebral, tactile, physical, and three-dimensional understanding of the small incision intrastromal technique is necessary to enable a successful transition to this new procedure, he noted.
SMILE is performed using a proprietary femtosecond laser (VisuMax 500 kHz, Carl Zeiss Meditec) to create an intrastromal lenticule that is then removed through a small side incision.
He noted that ease in dissecting and extracting the refractive lenticule improves as surgeons develop expertise working in a small three-dimensional space under a two-dimensional view.
“Experience performing cataract surgery provides a foundation for some of the necessary skills, but SMILE represents an entirely new concept in microsurgery,” he said.
“Various surgeons adopting SMILE have designed new instruments that enable dissection of the lenticule,” said Dr. Doane, an investigator in a U.S. clinical trial in which patients underwent SMILE in one eye and another refractive procedure, usually LASIK, in the fellow eye.
“Tools that are not specialized for SMILE will be too large, too sharp, and lacking the correct angulation,” he said.
Even using the proper tools, surgeons should anticipate a learning curve in performing SMILE.
Dr. Doane noted that in his first case, the lenticule dissection and extraction took almost 20 minutes as he proceeded carefully with his maneuvers to avoid causing any corneal injury.
However, he cut that time in half during his second case, and his confidence and efficiency continued to improve quickly thereafter.
“After several surgical days, I got to the point of being incredibly comfortable with SMILE so that the total surgical time was even less than for a LASIK procedure,” Dr. Doane said.
SMILE appears similar to LASIK with respect to refractive outcome accuracy when correcting low myopia, but appears to be even more predictable when treating higher myopia, Dr. Doane said.
He suggested the latter benefit of SMILE may be explained by the fact that environmental conditions do not affect the precision of the femtosecond laser intrastromal treatment whereas they influence the excimer laser ablation in LASIK.
“In a LASIK procedure, the laser ablation time for higher levels of correction may last 40 to 45 seconds,” Dr. Doane said. “During that time, the hydration state of the exposed corneal stroma can change, depending on room temperature, humidity, and barometric pressure.”
“The femtosecond laser treatment in SMILE is done in a closed system, and so the laser-tissue interaction is protected from influence of outside variables,” he said.
Surgeons and patients should be aware that visual recovery may be slightly slower after SMILE compared with LASIK.
“With LASIK we expect the ‘wow’ phenomenon where patients can see 20/20 or better uncorrected on the first day after surgery,” he said. “In my experience, we were not comparing results between procedures, but we did treat individual patients with LASIK in one eye and SMILE in the other eye.
“We found on the first postop day that vision was better by about 1 or 2 lines in the SMILE eye than in the LASIK eye in about one-third of patients, while the rest of the patients had better vision by about 1 or 2 lines in the LASIK eye,” Dr. Doane said.
By 1 week, this discrepancy resolved and the two groups of eyes saw the same.
John F. Doane, MD
This article was adapted from Dr. Doane’s presentation at the 2015 meeting of the American Society of Cataract and Refractive Surgery. Dr. Doane is a consultant to Carl Zeiss Meditec and receives funds for research overhead.