In 2001, femtosecond (FS) laser technology was introduced

Transcription

1 CLINICAL SCIENCE Clinical Outcomes After SMILE and Femtosecond Laser-Assisted LASIK for Myopia and Myopic Astigmatism: A Prospective Randomized Comparative Study Manli Liu, PhD, Yile Chen, PhD, Danyang Wang, PhD, Yugui Zhou, PhD, Xiaoying Zhang, BM, Jiexu He, BM, Ting Zhang, PhD, Yuan Sun, PhD, and Quan Liu, MD, PhD Purpose: To compare the clinical outcomes of small-incision lenticule extraction (SMILE) and femtosecond laser-assisted LASIK (FS-LASIK) for the correction of myopia and myopic astigmatism. Methods: In this prospective, randomized, comparative study, SMILE surgery was performed in 113 eyes with a mean spherical equivalent (MSE) of diopters (D) and FS-LASIK was performed in 84 eyes with an MSE of D. Contrast sensitivity and uncorrected and corrected distance visual acuities were measured preoperatively and 1 day, 1 week, 1, 3, and 6 months postoperatively. Higher-order aberrations were evaluated preoperatively and 6 months postoperatively. Results: At postoperative day 1, the uncorrected distance visual acuity in the FS-LASIK group was better (P, 0.05), whereas no statistically significant difference was found at 6 months postoperatively (P =0.9).Therewasnosignificant difference in terms of logmar corrected distance visual acuity and MSE during the 6 months of follow-up between the SMILE and FS-LASIK groups (all P. 0.05). The contrast sensitivity in the SMILE group was lower at 1 day and 1 week postoperatively (all P, 0.05). The spherical aberration at 6 mm diameter at 6 months postoperatively was lower (P, 0.05) in the SMILE group ( mm) than in the FS-LASIK group ( mm). Conclusions: Both FS-LASIK and SMILE procedures achieved good visual outcomes in the correction of myopia and myopic astigmatism. SMILE had a lower induction rate of spherical aberration at 6 months postoperatively in the analysis of 6 mm diameter than that of FS-LASIK. Received for publication May 29, 2015; revision received October 11, 2015; accepted October 15, From the Refractive Surgery Center, State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China. Supported by Grants from the Natural Science Foundation of Guangdong (2015A ). The authors have no conflicts of interest to disclose. M. Liu and Y. Chen contributed equally to this work. Reprints: Quan Liu, MD, PhD, State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, 54 S. Xianlie Road, Guangzhou , China ( drliuquan@163.com). Copyright 2015 Wolters Kluwer Health, Inc. All rights reserved. Key Words: small-incision lenticule extraction, femtosecond laserassisted LASIK, clinical outcomes, contrast sensitivity, higher-order aberrations (Cornea 2015;0:1 7) In 2001, femtosecond (FS) laser technology was introduced to create corneal flaps in laser in situ keratomileusis (LASIK). 1 FS-LASIK has gained wide acceptance in corneal refractive surgery because of its predictability, safety, and accuracy. 2 4 In 2011, the VisuMax FS laser system (Carl Zeiss Meditec AG, Jena, Germany) was introduced to perform small-incision lenticule extraction (SMILE) surgery for the correction of myopia and myopic astigmatism, 5 and it gained widespread acceptance because it is flapless, preserves more corneal nerves, and rarely causes dry eye Several studies have been conducted to report the refractive outcomes after SMILE 7,8,11 13 ; however, only a few articles compare the visual outcomes between SMILE and FS-LASIK procedures. 14,15 The purpose of this prospective study was to compare the visual and refractive outcomes at 6 months after FS-LASIK and SMILE for the correction of myopic refractive errors. PATIENTS AND METHODS Patients All procedures were approved by the Ethics Committee of Zhongshan Ophthalmic Center at the Sun Yat-sen University in accordance with the tenets of the Declaration of Helsinki. All recruited patients signed the consent letter. This prospective, randomized, comparative study included 197 eyes of 99 patients, and they either received SMILE (113 eyes of 57 patients, there was 1 emmetropic eye) or FS-LASIK surgery (84 eyes of 42 patients). All surgeries were performed by the same surgeon (Q.L.) following standard procedures at Zhongshan Ophthalmic Center (Guangzhou, China) between April and September The inclusion criteria were as follows: to diopters (D) of spherical equivalent (SE), 0 to D of cylinder with no history of ocular surgery and pathology, and residual stromal thickness. 250 mm. Monocular uncorrected and corrected distance visual acuities (UDVA and CDVA) using Snellen charts, ocular anterior segment by slit-lamp Cornea Volume 0, Number 0, Month

2 Liu et al Cornea Volume 0, Number 0, Month 2015 TABLE 1. Distribution of Preoperative Statistics of Subjects in SMILE and FS-LASIK Groups (Mean 6 SD) SMILE Group FS-LASIK Group P Age (yrs) (18 to 34) (18 to 34) 0.09 MR sphere (D) (29.25 to 21.50) (28.5 to 21.25) 0.85 MR cylinder (D) (24 to0) (23.5 to 0) 0.88 MRSE (D) (29.63 to 22.25) (29.25 to 21.38) 0.88 CDVA (logmar) (20.18 to 0) (20.18 to 0) 0.12 logmar, logarithm of the minimal angle; MR, manifest refraction. microscopy, and contrast sensitivity (CS) under different lighting conditions (Vector Vision CSV 1000E test, Vector Vision, USA) were measured preoperatively and 1 day, 1 week, and 1, 3, and 6 months postoperatively. Visual acuity from the Snellen chart was converted to logmar units using the Holladay method. The astigmatism was analyzed using the vector method of Alpins. 16 The CS was measured at a distance of 2.5 m in patient s CDVA under 4 different lighting conditions:photopic CS with and without glare and mesopic CS with and without glare at spatial frequencies of 3, 6, 12, and 18 cycles per degree (cpd). Wavefront aberrations in the 4 and 6 mm diameters were calculated with an aberrometer (Carl Zeiss Meditec, Jena, Germany) preoperatively and 6 months postoperatively. The root mean square (mm) was used to analyze the coma, trefoil, spherical, and residual fourthorder aberrations. SMILE Procedure SMILE surgery was performed with the VisuMax FS laser system (Carl Zeiss Meditec AG, Jena, Germany) with a 500-kHz repetition rate and a pulse energy of 180 nj by a sole fully qualified and highly experienced (.200 cases of SMILE) refractive surgeon (Q.L.) to avoid operative errors. Oxybuprocaine eye drops (Benoxil, Santen, Inc, Japan) were administered as topical anesthesia before the surgical procedure. The patients were positioned under the curved contact glass of the VisuMax FS laser and were asked to fixate at the target light, after which vacuum suction was activated to perform the treatment. The intended cap thickness was 120 mm. The diameter of the cap was 7.5 mm, 1.0 mm larger than the refractive lenticule (6.5 mm). Side cuts were set as 90 at a circumferential width of 2.0 mm to dissect the lenticule with spatulas (S02710 and S33427, Geuder) and extract with microforceps. FS-LASIK Procedure The FS-LASIK procedure was performed with the VisuMax FS laser system with a pulse of 140 nj and a repetition rate of 500 khz for the creation of corneal flaps. The WaveLight Allegretto excimer laser system (Alcon Laboratories, Inc, Fort Worth, TX) was used for stromal ablation. The intended diameter and flap thickness were 8.0 mm and 120 mm, respectively. The position and angle of the hinge were set at 90 and 50, respectively. The track and spot distances were set as 3.0 mm forflap creation and 1.5 mm for making the flap side cut. After lifting the flap, the excimer laser was used to perform stromal ablation, after which the flap was carefully repositioned over the stroma. After the SMILE and FS-LASIK surgeries, all patients were asked to use levofloxacin eye drops (Santen Pharmaceutical Co, Ltd) 4 times a day for 2 weeks, tobramycin and dexamethasone eye drops (TobraDex; SA Alcon-Couvreur NV) 4 times a day during the first week after surgery, loteprednol etabonate ophthalmic suspension FIGURE 1. Cumulative percentage of eyes that achieved definite cumulative levels of UDVA over 6 months of follow-up. All eyes in both groups were included. 2 Copyright 2015 Wolters Kluwer Health, Inc. All rights reserved.

3 Cornea Volume 0, Number 0, Month 2015 Clinical Outcomes After SMILE and FS-LASIK TABLE 2. UDVA and CDVA During the Period of Follow-up in SMILE and FS-LASIK Groups logmar UDVA logmar CDVA SMILE Group FS-LASIK Group P SMILE Group FS-LASIK Group P 1 d , wk mo mo mo (Lotemax, Bausch & Lomb Inc) 4 times a day during the second week after surgery, and sodium hyaluronate eye drops (Ursapharm Arzneimittel GmbH, Germany) 4 times a day for 1 month. Statistical Analyses All statistical analyses were performed with IBM SPSS Statistics 19.0 (SPSS Inc, Chicago, IL). One-way analysis of variance (ANOVA) was used for the analysis of timely changes postoperatively, and the Dunnett test was used for multiple comparisons. Normality was checked by the Kolmogorov Smirnov test, and the 2-tailed Student t-test was used to compare the data between the SMILE and FS-LASIK groups. Mean 6 SD was used for quantitative variables. The significance level was set at P, RESULTS Study Population The demographics of this study are summarized in the Table 1. All surgeries were uneventful and no definite intraoperative complications were observed. There were no significant differences in terms of age (2-tailed Student t-test, P = 0.09), manifest spherical diopter (P = 0.85), manifest cylindrical diopter (P = 0.88), manifest SE (P = 0.88), or logmar CDVA (P = 0.12) between the FS-LASIK and SMILE groups preoperatively. Effectiveness At 1 day, 1 week, 1, 3, and 6 months after surgery, there were 55%, 89%, 93%, 96%, and 96% of treated eyes in the SMILE group, and 73%, 95%, 96%, 99%, and 99% treated eyes in the FS-LASIK group, respectively, that had 20/20 or better UDVA (Fig. 1). A statistically significant difference of logmar UDVA was found between the SMILE ( ) and FS-LASIK ( ) groups (P, 0.05) at 1 day postoperatively. However, this trend did not extend to all time points as there was no significant difference at 1 week and 1, 3, and 6 months postoperatively (Table 2). Safety Outcomes Regarding the CDVA at 1 week postoperatively, in the SMILE group, 53 eyes (47%) showed no change, 28 eyes (25%) gained 1 line, 3 eyes (3%) gained more than 1 line, 26 eyes (23%) lost 1 line, and 3 eyes (3%) lost more than 1 line, whereas in the FS-LASIK group, 46 eyes (55%) exhibited no change, 25 eyes (30%) gained 1 line, 1 eye (1%) gained more than 1 line, 11 eyes (13%) lost 1 line, and 1 eye (1%) lost more than 1 line at 1 week postoperatively. At 6 months postoperatively, in the SMILE group, 87 eyes (77%) showed no change, 17 eyes (15%) gained 1 line, 2 eyes (2%) gained more than 1 line, 5 eyes (4%) lost 1 line, and 2 eyes (2%) lost 2 lines (both patients had a 20/20 UDVA and had satisfactory visual acuity), whereas in the FS-LASIK group, 55 eyes (65%) exhibited no change, 24 eyes (29%) gained 1 line, 1 eye (1%) gained more than 1 line, 4 eyes (5%) FIGURE 2. Percentage of eyes in gain/loss of lines of CDVA at different time points of follow-up after SMILE and FS-LASIK surgeries. All eyes in both groups were included. Copyright 2015 Wolters Kluwer Health, Inc. All rights reserved. 3

4 Liu et al Cornea Volume 0, Number 0, Month 2015 FIGURE 3. Scatterplot of the attempted against achieved manifest SE correction at 6 months after SMILE and FS-LASIK surgeries. lost 1 line, and no eye was lost more than 1 line at 6 months postoperatively (Fig. 2). There was no statistically significant difference in logmar CDVA between both groups at all time points postoperatively (P. 0.05) (Table 2) D (range: D) in the SMILE group and D (range: D) in the FS-LASIK group from 1 week to 6 months after surgery, which were not considered significantly different (P = 0.23). Predictability A scatterplot of the attempted SE against achieved SE correction is shown in Figure 3. At 6 months postoperatively, all treated eyes were within D (achieved vs. attempted correction); 97% and 100% of eyes in the SMILE and FS-LASIK groups, respectively, were within D (Fig. 4). There was no significant difference in manifest refraction between both groups at at any time point postoperatively (P. 0.05) (Table 3). Stability The change in the manifest SE is shown in Figure 5. There were 2.6% and 7.1% of treated eyes with a change of.0.50 D in SE from 1 week to 6 months after SMILE and LASIK, respectively. The changes in manifest refraction were Refractive Astigmatism Refractive astigmatism results are shown in Figure 6 with scatterplots of the target-induced astigmatism vector (TIA) versus the surgically induced astigmatism vector (SIA), the percentage of eyes that achieved definite levels of astigmatism, and the corresponding distribution of the angle of error at 6 months after SMILE and FS-LASIK surgeries. There were no significant differences between the SMILE and FS-LASIK surgeries in the arithmetic means of TIA (P = 0.88), SIA (P = 0.84), and angle of error (P =0.96). CS Under Different Lighting Condition At 1 day, 16 patients in the SMILE group and 4 patients in the FS-LASIK group had not finished the CS examination FIGURE 4. Accuracy of SE at 6 months postoperatively. The percentage of eyes that reached definite differences in attempted versus achieved correction for both groups. All eyes in both groups were included. 4 Copyright 2015 Wolters Kluwer Health, Inc. All rights reserved.

5 Cornea Volume 0, Number 0, Month 2015 Clinical Outcomes After SMILE and FS-LASIK TABLE 3. Manifest Refraction During the Period of Follow-up in SMILE and FS-LASIK Groups Parameters SMILE Group FS-LASIK Group P MR sphere (D) 1wk mo mo mo MR cylinder (D) 1wk mo mo mo MRSE (D) 1wk mo mo mo MR, manifest refraction. because of corneal edema or symptoms of corneal irritation. In the SMILE group, the CS at spatial frequencies of 3 cpd and 6 cpd under different lighting conditions recovered to the preoperative level at 1 week postoperatively, but 12 cpd and 18 cpd recovered to the preoperative level at 1 month postoperatively. In the FS-LASIK group, the CS at spatial frequencies of 3, 6, 12, and 18 cpd under different lighting conditions recovered to the preoperative level at 1 week postoperatively (Fig. 7). Wavefront Aberrations We compared the induced ocular aberrations (the root mean square of coma, trefoil, spherical aberration, and the residual fourth-order aberration) between the SMILE and FS- LASIK groups (Table 4). Six months after surgery, in the 4- mm zone, there was no significant difference in wavefront aberrations between both groups (P = 0.048), so the induction of coma can be considered to be very little or not significant between both groups; however, in the 6-mm zone, SMILE had significantly lower induction rates of spherical aberrations than those of FS-LASIK (P, 0.001). DISCUSSION In this study, both SMILE and FS-LASIK procedures have shown excellent efficacy, probable safety, and predictability for the correction of myopia and myopic astigmatism. We observed time-dependent changes in refractive outcomes before and after SMILE and FS-LASIK. The values of UDVA, CDVA, and SE in both SMILE and FS-LASIK groups were not significantly different between 1 week and 6 months after surgery. When comparing the percentage of eyes with a UDVA 20/20 or better between both groups at 3 and 6 months of follow-up, we found that the results in the FS-LASIK group (99%) were better than in the SMILE group (96%). Four eyes with high myopia ( D) in the SMILE group did not achieve a UDVA of 20/20 at 3 and 6 months postoperatively. All groups had satisfactory visual outcomes at 6 months postoperatively. Our results are similar to those reported by Lin et al. 14 They reported that no significant differences were found in refractive diopters between SMILE and FS-LASIK groups at 1 and 3 months postoperatively. However, we found better differences in the UDVA after FS-LASIK than SMILE at 1 day after surgery. This difference in the recovery time of visual acuity after SMILE and FS-LASIK was probably due to the difference in the healing response between both treatment procedures. As previously described, the SMILE procedure 5,17 entails attaching the posterior surface of the cap to the residual stromal bed after extracting the lenticule, which is different from the LASIK procedure. Vestergaard et al, 18 Heichel et al, 19 and Shah and Shah 20 reported that slit-lamp examination showed transient hyperreflection in the interface in some eyes after femtosecond lenticule extraction (FLEx) within 1 week postoperatively; Agca et al 21 reported that treated eyes after SMILE have increased corneal backscatter in the interface at 3 months after extracted lenticule surgery compared with the FS-LASIK procedure. They also suggested that the stromal damage could be related to the FS laser treatment and the surgical maneuvers required for blunt separation of the lenticule floor and roof. 21 Another reason for the delayed visual recovery may be corneal edema. Regarding CS, Sekundo et al 12 found that neither mesopic nor photopic CS showed any significant changes at 1 year after SMILE. In another comparative analysis of CS after SMILE and FS-LASIK, both procedures yielded no statistically significant differences from baseline to 6 months after surgery. 22 In our study, the postoperative CS was lower in the SMILE group FIGURE 5. Stability of visual outcomes during the period of follow-up in SMILE and FS-LASIK groups. Copyright 2015 Wolters Kluwer Health, Inc. All rights reserved. 5

6 Liu et al Cornea Volume 0, Number 0, Month 2015 FIGURE 6. Vector analysis for SMILE and FS-LASIK at 6 months postoperatively. Target-induced astigmatism vector versus surgically induced astigmatism vector after (A) SMILE and (B) FS-LASIK. C, Percentage of eyes that achieved definite levels of astigmatism after SMILE (black) and FS-LASIK (gray). D, Distribution of the angle of error after SMILE (black) and FS-LASIK (gray). than in the FS-LASIK group at 1 day and 1 week postoperatively; however, there were no statically significant differences found in SMILE and FS-LASIK surgeries from 1 month onward. Both groups showed significant improvement in CS at low spatial frequencies (3 and 6 cpd) but no improvement at high spatial frequencies (12 and 18 cpd) at 6 months postoperatively. After FS-LASIK, there was faster recovery of CS at high spatial frequencies under all different lighting conditions as compared with that seen after SMILE surgeries. This may result from the different mechanism of corneal stromal wound-healing processes after both procedures. In our study, we found that SMILE had significantly lower induction rates of spherical aberrations at the analysis diameter of 6mm(P, 0.001). These are similar to the results reported by Lin et al 14 and Ganesh and Gupta. 15 Gyldenkerne et al 23 also found that in the diameter of 5 mm, FS-LASIK induced more coma and spherical aberration than did SMILE. The results were also comparable with the findings of our study. As we know, there is no transition zone of the SMILE procedure, and it could achieve a larger ablation zone than do FS-LASIK procedures. However, postoperative spherical aberration was associated with optical and ablation zones. 24 The larger diameter optical zones could have decreased the induction of higher-order aberrations after LASIK. 25,26 We have further confirmed it in our study as the optical zone was significantly larger in the SMILE group than in the FS-LASIK group (the range of the transition zone was mm, and the range for the optical zone was,6.5 mm). Further research is still needed to compare both procedures on the basis of the same ablation zone. Additionally, the different healing procedures correlated with corneal remodeling may attribute to the higher-order aberrations. 27 To improve the optical interface quality, Zhao et al 28 developed a new continuous curvilinear lenticulerrhexis technique for SMILE. Overall, in this study, both SMILE and FS-LASIK have shown probable safety, effectiveness, and predictability for correction of myopia and myopic astigmatism; however, SMILE has a lower induction rate of spherical aberration at 6 months after surgery. It is necessary to confirm these results FIGURE 7. CS at spatial frequencies of 3, 6, 12, and 18 cpd under photopic, mesopic, photopic with glare, and mesopic with glare lighting conditions in SMILE and FS-LASIK groups over 6 months of follow-up. 6 Copyright 2015 Wolters Kluwer Health, Inc. All rights reserved.

7 Cornea Volume 0, Number 0, Month 2015 Clinical Outcomes After SMILE and FS-LASIK TABLE 4. Comparison of Changed in Root Mean Square Values of Different Aberrations Between Both Groups for 4- and 6-mm Analysis Diameters at 6 Months Postoperatively (Induced = Postoperative Values 2 Preoperative Values) Parameter (RMS, mm) SMILE Group FS-LASIK Group P 4mm Pre Coma Trefoil Spherical Residual fourth order Post Coma Trefoil Spherical Residual fourth order Induced Coma Trefoil Spherical Residual fourth order mm Pre Coma Trefoil Spherical Residual fourth order Post Coma Trefoil Spherical ,0.01* Residual fourth order Induced Coma Trefoil Spherical ,0.01* Residual fourth order coma, RMS for Z 21 3 and Z 1 3 ; residual fourth-order, RMS for Z22 4,Z2 4,Z24 4 and Z 4 4 ; RMS, root mean square; spherical, RMS for jz 0 4j; trefoil, RMS for Z23 3 and Z 3 3. *Values differed significantly from 2 groups (P, 0.01). with further studies with a larger numbers of eyes and a longer follow-up period. In addition, preoperative spherical and cylindrical diopter should be considered as a grouping criterion in the patient population. REFERENCES 1. Ratkay-Traub I, Juhasz T, Horvath C, et al. Ultra-short pulse (femtosecond) laser surgery: initial use in LASIK flap creation. Ophthalmol Clin North Am. 2001;14: Kymionis GD, Kankariya VP, Plaka AD, et al. Femtosecond laser technology in corneal refractive surgery: a review. J Refract Surg. 2012;28: Tanna M, Schallhorn SC, Hettinger KA. Femtosecond laser versus mechanical microkeratome: a retrospective comparison of visual outcomes at 3 months. J Refract Surg. 2009;25:S668 S Montes-Mico R, Rodriguez-Galietero A, Alio JL. Femtosecond laser versus mechanical keratome LASIK for myopia. Ophthalmology. 2007; 114: Sekundo W, Kunert KS, Blum M. Small incision corneal refractive surgery using the small incision lenticule extraction (SMILE) procedure for the correction of myopia and myopic astigmatism: results of a 6 month prospective study. Br J Ophthalmol. 2011;95: Vestergaard A, Ivarsen AR, Asp S, et al. Small-incision lenticule extraction for moderate to high myopia: predictability, safety, and patient satisfaction. J Cataract Refract Surg. 2012;38: Kamiya K, Shimizu K, Igarashi A, et al. Visual and refractive outcomes of femtosecond lenticule extraction and small-incision lenticule extraction for myopia. Am J Ophthalmol. 2014;157: Ivarsen A, Asp S, Hjortdal J. Safety and complications of more than 1500 small-incision lenticule extraction procedures. Ophthalmology. 2014; 121: Li M, Niu L, Qin B, et al. Confocal comparison of corneal reinnervation after small incision lenticule extraction (SMILE) and femtosecond laser in situ keratomileusis (FS-LASIK). PLoS One. 2013;8:e Denoyer A, Landman E, Trinh L, et al. Dry eye disease after refractive surgery: comparative outcomes of small incision lenticule extraction versus LASIK. Ophthalmology. 2015;122: Xu Y, Yang Y. Small-incision lenticule extraction for myopia: results of a 12-Month prospective study. Optom Vis Sci. 2015;92: Sekundo W, Gertnere J, Bertelmann T, et al. One-year refractive results, contrast sensitivity, high-order aberrations and complications after myopic small-incision lenticule extraction (ReLEx SMILE). Graefes Arch Clin Exp Ophthalmol. 2014;252: Kunert KS, Melle J, Sekundo W, et al. One-year results of small incision lenticule extraction (SMILE) in myopia [in German]. Klin Monbl Augenheilkd. 2015;232: Lin F, Xu Y, Yang Y. Comparison of the visual results after SMILE and femtosecond laser-assisted LASIK for myopia. J Refract Surg. 2014;30: Ganesh S, Gupta R. Comparison of visual and refractive outcomes following femtosecond laser- assisted lasik with smile in patients with myopia or myopic astigmatism. J Refract Surg. 2014;30: Alpins N. Astigmatism analysis by the Alpins method. J Cataract Refract Surg. 2001;27: Shah R, Shah S, Sengupta S. Results of small incision lenticule extraction: all-in-one femtosecond laser refractive surgery. J Cataract Refract Surg. 2011;37: Vestergaard A, Ivarsen A, Asp S, et al. Femtosecond (FS) laser vision correction procedure for moderate to high myopia: a prospective study of ReLEx((R)) flex and comparison with a retrospective study of FS-laser in situ keratomileusis. Acta Ophthalmol. 2013;91: Heichel J, Blum M, Duncker GI, et al. Surface quality of porcine corneal lenticules after Femtosecond Lenticule Extraction. Ophthalmic Res. 2011;46: Shah R, Shah S. Effect of scanning patterns on the results of femtosecond laser lenticule extraction refractive surgery. J Cataract Refract Surg. 2011;37: Agca A, Ozgurhan EB, Yildirim Y, et al. Corneal backscatter analysis by in vivo confocal microscopy: fellow eye comparison of small incision lenticule extraction and femtosecond laser-assisted LASIK. J Ophthalmol. 2014;2014: Vestergaard AH, Grauslund J, Ivarsen AR, et al. Efficacy, safety, predictability, contrast sensitivity, and aberrations after femtosecond laser lenticule extraction. J Cataract Refract Surg. 2014;40: Gyldenkerne A, Ivarsen A, Hjortdal JO. Comparison of corneal shape changes and aberrations induced by FS-LASIK and SMILE for myopia. J Refract Surg. 2015;31: Vega-Estrada A, Alio JL, Arba MS, et al. Corneal higher order aberrations after LASIK for high myopia with a fast repetition rate excimer laser, optimized ablation profile, and femtosecond laser-assisted flap. J Refract Surg. 2012;28: Buhren J, Kuhne C, Kohnen T. Influence of pupil and optical zone diameter on higher-order aberrations after wavefront-guided myopic LASIK. J Cataract Refract Surg. 2005;31: Mok KH, Lee VW. Effect of optical zone ablation diameter on LASIKinduced higher order optical aberrations. J Refract Surg. 2005;21: Dong Z, Zhou X, Wu J, et al. Small incision lenticule extraction (SMILE) and femtosecond laser LASIK: comparison of corneal wound healing and inflammation. Br J Ophthalmol. 2014;98: Zhao Y, Li M, Yao P, et al. Development of the continuous curvilinear lenticulerrhexis technique for small incision lenticule extraction. J Refract Surg. 2015;31: Copyright 2015 Wolters Kluwer Health, Inc. All rights reserved. 7