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US Ophthalmic Review Highlights Small Incision Lenticule Extraction (SMILE) in 2015 Dan Z Reinstein, MD, MA(Cantab), FRCSC, DABO, FRCOphth, FEBO Medical Director, London Vision Clinic, London, UK; Clinical Professor of Ophthalmology, Department of Ophthalmology, Columbia University Medical Center, New York, NY, US; Clinical Professor of Ophthalmology, Centre Hospitalier National d’Ophtalmologie, Paris, France Abstract Following the early work by Sekundo et al. and Shah et al., small incision lenticule extraction (SMILE) using the VisuMax femtosecond laser (Carl Zeiss Meditec) has become increasingly popular. The accuracy of the lenticule dimensions has been verified using very- high-frequency digital ultrasound and optical coherence tomography. Visual and refractive outcomes and safety have been shown to be similar to LASIK. A number of studies have demonstrated a lower reduction and faster recovery of corneal sensitivity and subbasal nerve fiber density after SMILE than LASIK, as expected since the anterior stroma is disturbed only by the small incision. The potential biomechanical advantages of SMILE have been modeled based on the nonlinearity of tensile strength through the stroma. Extraction of an intact lenticule has also given rise to new applications such as cryopreservation of the lenticule for later reimplantation, and a new procedure, endokeratophakia, in which a myopic SMILE lenticule is implanted into a hyperopic patient. Keywords Small incision lenticule extraction (SMILE), femtosecond laser, keyhole, flapless procedure Disclosure: Dan Z Reinstein, MD, MA(Cantab), FRCSC, DABO, FRCOphth, FEBO, is a consultant for Carl Zeiss Meditec (Jena, Germany) and has a proprietary interest in the Artemis technology (ArcScan Inc, Morrison, Colorado) and is an author of patents related to VHF digital ultrasound administered by the Cornell Center for Technology Enterprise and Commercialization (CCTEC), Ithaca, New York. No funding was received in the publication of this article. Open Access: This article is published under the Creative Commons Attribution Noncommercial License, which permits any noncommercial use, distribution, adaptation, and reproduction provided the original author(s) and source are given appropriate credit. Received: January 4, 2015 Accepted: January 8, 2015 Citation: US Ophthalmic Review, 2015;8(1):30–2 Correspondence: Dan Z Reinstein, MD, MA(Cantab), FRCSC, DABO, FRCOphth, FEBO, London Vision Clinic, 138 Harley Street, London W1G 7LA, UK. E: Ever since femtosecond lasers were first introduced into refractive surgery, the ultimate goal has been to create an intrastromal lenticule that can then be removed in one piece manually, thereby circumventing the need for incremental photoablation by an excimer laser. This was achieved in 2005, presented at the American Academy of Ophthalmology (AAO) meeting in Las Vegas in 2006, and published in 2008 with the Femtosecond Lenticule Extraction procedure (FLEx) in which a lenticule was manually removed after lifting a flap, 1 11 years after this had first been demonstrated in rabbit eyes with a picosecond laser. 2 Following the successful implementation of FLEx, a new procedure called small incision lenticule extraction (SMILE) was developed; an all-femtosecond laser, keyhole, flapless procedure that is in the process of revolutionizing corneal refractive surgery and realizing Jose Ignacio Barraquer’s original concept of keratomileusis. 3,4 The SMILE procedure is gaining popularity following the results of the first prospective trials 5–7 and more recent reports that have demonstrated that the visual and refractive outcome is similar to laser in situ keratomileusis (LASIK), 8–18 and there have now been over 140,000 procedures performed worldwide with more than 300 surgeons regularly doing SMILE. The feasibility of the procedure has been proved by studies on the surface quality of the lenticules, 19,20 wound healing and inflammation, 21–23 and the accuracy of the lenticule thickness parameters have been verified using very-high-frequency digital ultrasound 24,25 and optical coherence tomography (OCT). 26–29 166 The safety has also been demonstrated to be similar to LASIK 30 and our recent publication has shown that there are no concerns in treating patients with SMILE for low myopia. 17 In terms of safety, SMILE also brings two advantages over LASIK, relevant to the most common complication: dry eye, and the most serious complication: ectasia. Both of these advantages stem from the minimally invasive pocket incision nature of the procedure as this results in maximal retention of anterior corneal innervational as well as structural integrity. It was expected that there would be less postoperative dry eye after SMILE. While the trunk nerves that ascend into the epithelial layer within the diameter of the cap will continue to be severed in SMILE, those that ascend outside the cap diameter, or that are anterior to the cap interface will be spared. A number of studies have demonstrated a lower reduction and faster recovery of corneal sensitivity after SMILE than LASIK, 31–39 with recovery to baseline after 3–6 months after SMILE compared with 6–12 months after LASIK. Some studies have also used confocal microscopy to demonstrate a lower decrease in sub-basal nerve fiber density after SMILE than LASIK. 34,38,40 The other major advantage of SMILE is the biomechanical profile as the anterior stroma above the lenticule remains uncut (except in the location of the small incision), unlike in LASIK where anterior stromal lamellae are severed by the creation of the flap. It has been TOU C H ME D ICA L ME D IA