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      Astigmatism Correction Using SMILE

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          Abstract

          Small incision lenticule extraction (SMILE) was introduced in the recent decade for the treatment of myopia and myopic astigmatism. This flap-free technique has a high efficacy and safety profile and also carries potential advantages over laser in situ keratomileusis such as a better corneal biomechanical stability, reduction in dry eyes rate, and the avoidance of flap complications. However, there have been concerns regarding the precision of astigmatism correction that undercorrection has been reported to be apparent. Various factors that affect astigmatism correction have been identified in the literature. The purpose of this review is to discuss the factors that affect astigmatism correction in SMILE and several techniques to improve the refractive outcomes.

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          Results of small incision lenticule extraction: All-in-one femtosecond laser refractive surgery.

          To report the clinical results of small incision lenticule extraction to correct refractive errors using a femtosecond laser to refine the femtosecond lenticule extraction technique. Private laser center, Vadodara, India. Prospective clinical study. The VisuMax femtosecond laser system was used to perform small incision lenticule extraction to treat refractive errors. The laser was used to cut a refractive lenticule intrastromally to correct myopia and myopic astigmatism. The lenticule was then extracted from the stroma through a 3.0 to 5.0 mm incision. Outcome measures were corrected distance visual acuity (CDVA), uncorrected distance visual acuity (UDVA), and manifest refraction during 6 months of follow-up. Corneal topography and ocular wavefront aberrations were also measured. The study enrolled 51 eyes of 41 patients. The mean spherical equivalent was -4.87 diopters (D) ± 2.16 (SD) preoperatively and +0.03 ± 0.30 D 6 months postoperatively. Refractive stability was achieved within 1 month (P<.01). Six months after surgery, 79% of all full-correction cases had a UDVA of 20/25 or better. The 6-month postoperative CDVA was the same as or better than the preoperative CDVA in 95% of eyes. Two eyes lost 1 line of CDVA. All-in-one femtosecond refractive correction using a small incision technique was safe, predictable, and effective in treating myopia and myopic astigmatism. No author has a financial or proprietary interest in any material or method mentioned. Additional disclosure is found in the footnotes. Copyright © 2011 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.
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            Safety and complications of more than 1500 small-incision lenticule extraction procedures.

            To evaluate the safety and complications of small-incision lenticule extraction (SMILE). Clinical control cohort study. A total of 922 healthy patients (1800 eyes) who were treated for myopia or myopic astigmatism between January 2011 and March 2013 at the Department of Ophthalmology, Aarhus, Denmark. Patients received a full preoperative examination and were treated with SMILE in both eyes and followed for 3 months (1574 eyes). Patients with complications, including loss of corrected distance visual acuity (CDVA) or dissatisfaction, were offered a late reexamination. Surgical complications and CDVA. Mean preoperative spherical equivalent refraction was -7.25±1.84 diopters (D). Average postoperative refraction was -0.28±0.52 D, and mean error of treatment was -0.15±0.50 D. By 3 months, 86% (1346 eyes) had unchanged or improved CDVA. A loss of 2 or more lines was observed in 1.5% of eyes; however, at a late follow-up visit (average, 18 months), CDVA was within 1 line of the preoperative level in all eyes. Perioperative complications included epithelial abrasions (6%), small tears at the incision (1.8%), and difficult lenticule extraction (1.9%). The cap was perforated in 4 eyes, and a major tear occurred in 1 eye; however, none of these patients had late visual symptoms. In 0.8% (14 eyes), suction was lost during surgery. Re-treatment was successful in 13 eyes, whereas 1 eye had ghost images and was re-treated with topography-guided photorefractive keratectomy (PRK). Postoperative complications included trace haze (8%), epithelial dryness on day 1 (5%), interface inflammation secondary to central abrasion (0.3%), and minor interface infiltrates (0.3%); these complications had an impact on CDVA at 3 months in only 1 case. Irregular corneal topography occurred in 1.0% of eyes, resulting in reduced 3-month CDVA (12 eyes) or ghost images (6 eyes). Topography-guided PRK was performed in 4 eyes, with improvement in 3 cases. Satisfaction was high, with only 2 patients dissatisfied at their latest visit because of blurred vision or residual astigmatism. Overall, SMILE had acceptable safety. Although 1.5% of eyes had reduced CDVA by 3 months, visual acuity was restored in the long term. Likewise, patient satisfaction was high. Copyright © 2014 American Academy of Ophthalmology. Published by Elsevier Inc. All rights reserved.
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              Mathematical model to compare the relative tensile strength of the cornea after PRK, LASIK, and small incision lenticule extraction.

              To develop a mathematical model to estimate the relative differences in postoperative stromal tensile strength following photorefractive keratectomy (PRK), LASIK, and small incision lenticule extraction (SMILE). Using previously published data where in vitro corneal stromal tensile strength was determined as a function of depth, a mathematical model was built to calculate the relative remaining tensile strength by fitting the data with a fourth order polynomial function yielding a high correlation coefficient (R(2) = 0.930). Calculating the area under this function provided a measure of total stromal tensile strength (TTS), based only on the residual stromal layer for PRK or LASIK and the residual stromal layers above and below the lenticule interface for SMILE. Postoperative TTS was greatest after SMILE, followed by PRK, then LASIK; for example, in a 550-μm cornea after 100-μm tissue removal, postoperative TTS was 75% for SMILE (130-μm cap), 68% for PRK, and 54% for LASIK (110-μm flap). The postoperative TTS decreased for thinner corneal pachymetry for all treatment types. In LASIK, the postoperative TTS decreased with increasing flap thickness by 0.22%/μm, but increased by 0.08%/μm for greater cap thickness in SMILE. The model predicted that SMILE lenticule thickness could be approximately 100 μm greater than the LASIK ablation depth and still have equivalent corneal strength (equivalent to approximately 7.75 diopters). This mathematical model predicts that the postoperative TTS is considerably higher after SMILE than both PRK and LASIK, as expected given that the strongest anterior lamellae remain intact. Consequently, SMILE should be able to correct higher levels of myopia. Copyright 2013, SLACK Incorporated.
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                Author and article information

                Journal
                Asia Pac J Ophthalmol (Phila)
                Asia Pac J Ophthalmol (Phila)
                AP9
                Asia-Pacific Journal of Ophthalmology (Philadelphia, Pa.)
                Department of Ophthalmology & Visual Sciences, The Chinese University of Hong Kong
                2162-0989
                Sep-Oct 2019
                04 October 2019
                : 8
                : 5
                : 391-396
                Affiliations
                []Department of Ophthalmology, Grantham Hospital, Hong Kong, China
                []Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong, China
                []Department of Ophthalmology, Hong Kong Sanatorium & Hospital, Hong Kong, China
                [§ ]Department of Ophthalmology and Visual Sciences, The Chinese University of Hong Kong, Hong Kong, China
                Author notes
                Correspondence: Tommy C.Y. Chan, Department of Ophthalmology, Hong Kong Sanatorium & Hospital, 2 Village Road, Happy Valley, Hong Kong 852, China. E-mail: tommychan.me@ 123456gmail.com .
                Article
                APJO-2019-207
                10.1097/01.APO.0000580140.74826.f5
                6784860
                31490198
                152cdb23-a193-493a-942e-c0dcfd9b5f1c
                Copyright © 2019 Asia-Pacific Academy of Ophthalmology. Published by Wolters Kluwer Health, Inc. on behalf of the Asia-Pacific Academy of Ophthalmology.

                This is an open access article distributed under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives License 4.0 (CCBY-NC-ND), where it is permissible to download and share the work provided it is properly cited. The work cannot be changed in any way or used commercially without permission from the journal. http://creativecommons.org/licenses/by-nc-nd/4.0

                History
                : 17 May 2019
                : 17 June 2019
                Categories
                Review Article
                Custom metadata
                TRUE

                astigmatism,lenticule extraction,myopia,smile
                astigmatism, lenticule extraction, myopia, smile

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