Laser vision correction enjoys a position as the most commonly performed elective surgery in the world,1 owing to its excellent safety profile and high patient-reported satisfaction rate.2 Currently, the three modalities that are widely used are laser in situ keratomileusis (LASIK), photorefractive keratectomy (PRK), and small incision lenticule extraction (SMILE). In excimer laser surgery, conventional ablation simply corrects spherocylindrical error, but often results in induction of unwanted higher order aberrations.3 For that reason, different customized forms of ablations have been developed.3,4 These include algorithms that aim to minimize induction of aberrations and compensate for the so-called “cosine effect” (the reduction in ablation efficacy toward the periphery, mainly responsible for spherical aberration induction), preserve the natural shape of the cornea, or intend to correct corneal irregularities based on corneal topography.3,4
To obtain approval for use in the United States of America, lasers used for vision correction must undergo rigorous premarket approval studies for review by the U.S. Food and Drug Administration (FDA), yielding a wealth of information about the performance of the technique. A thorough understanding of these data is helpful for clinicians as they navigate which treatment algorithms and laser platform to use in patient care. Although a comparison of FDA premarket approval (PMA) data of wavefront- and topography-guided LASIK has been previously performed,5,6 to our knowledge, this is the first study reviewing the FDA PMA data of SMILE for myopia with astigmatism and two recently approved customized forms of LASIK. Refractive and visual data and astigmatic outcomes between the three procedures are compared in this study.
Patients and Methods
Outcomes of three recent FDA PMA studies for the correction of spherocylindrical myopia were reviewed: VisuMax SMILE7 (Carl Zeiss Meditec AG, Jena, Germany) (SMILE group), topography-guided LASIK performed with the Allegretto Wave Eye-Q excimer laser system8 (Alcon Laboratories, Inc., Fort Worth; TX) (TOPO group), and wavefront-guided LASIK performed with the STAR S4 IR excimer laser system9 (Johnson & Johnson Vision Care, Inc., Santa Ana, CA) (WFG group). All three studies were conducted as prospective, nonrandomized, multicenter studies in the United States and followed strict protocols for clinical trials with the approval of local institutional review boards and appropriate informed consent documents obtained from all study participants.
The refractive inclusion criteria of the SMILE study were for the treatment of myopia with magnitude up to 10.00 D and cylinder up to 3.00 D, with no more than 11.50 D of manifest spherical equivalent (MSE). The TOPO group included patients with myopic sphere up to 9.00 D, cylinder up to 6.00 D, and MSE up to 9.00 D. In the WFG study, the inclusion criteria were myopic sphere of 12.00 D or less, cylinder up to 8.00 D, and MSE of 12.00 D or less.
All studies adhered to similar inclusion/exclusion criteria, which are customary for corneal refractive procedures. The minimum patient age for the SMILE study was 22 years, whereas the TOPO and WFG studies included patients 18 years and older.
The exclusion criteria in all three studies were: abnormal corneal topography or any other abnormal corneal findings, clinically significant dry eye, anterior segment pathology; residual, recurrent, or active ocular disease; previous intraocular or corneal surgery, systemic autoimmune diseases that might affect wound healing, and pregnancy/lactation. A detailed list of all inclusion/exclusion criteria is presented in each study.7–9
In all three studies, patients were observed for up to 12 months, with the visits scheduled at 1 day, 1 week, and 1, 3, 6, 9, and 12 months. The main clinical variables compared in this report were uncorrected (UDVA) and corrected (CDVA) visual acuity, manifest refractive error, and vector analysis of refractive cylinder.
The SMILE procedure was performed using the VisuMax femtosecond laser system (Carl Zeiss Meditec AG), with 3 × 3 µm or 4.5 × 4.5 µm spot spacing and pulse energies between 125 and 170 nJ. The treatment was based on the patient's manifest refraction and centered on the corneal vertex. The cap thickness was set to 120 µm, with an intended cap diameter of 7.5 mm, whereas the diameter of the refractive lenticule was 6 to 6.5 mm. The refractive lenticule was dissected and manually removed through a small incision cut with forceps.
For the TOPO treatment, corneal topographies were obtained prior to the treatment with the Allegro Topolyzer (Alcon Laboratories, Inc.). The T-CAT software used the topography data and clinical refraction to calculate the LASIK treatment plan. Optical, transition, and ablation zones were determined based on the patient's individual measurements and the treatments were performed with the Allegretto Wave Eye-Q excimer laser. The laser uses an automated centering mode and pupil tracking for centering ablations.
For the WFG treatments, the ablation profile was derived from a Hartmann-Shack wavefront aberrometer (iDesign Advanced WaveScan Studio; Johnson & Johnson Vision Care, Inc.). The device captures spherocylindrical refraction and higher order aberrations to calculate the treatment plan, which is then transferred to the excimer laser (STAR S4 IR excimer laser system; Johnson & Johnson Vision Care, Inc.). All treatments were performed with an optical zone of 6 mm and an ablation zone of 8 mm. The system uses automated iris registration and pupil tracking.
Primary clinical outcomes were extracted from each study for the available follow-up visits. The chi-square test was used to compare percentages and, if necessary, Bonferroni post-hoc correction was applied to find differences between paired groups.
To present astigmatism outcomes, all three studies used vector analysis as described by Eydelman et al.10 The main outcomes of vector analysis were compared for each study for the follow-up month when the refractive stability was achieved. All calculations were performed with Microsoft Office Excel software version 11.0 (Microsoft Corporation, Redmond, WA) and STATISTICA (StatSoft Inc., College Station, TX) software.
The number of eyes successfully treated in the SMILE, TOPO, and WFG groups was 304, 249, and 334, respectively. Table 1 presents the basic demographics and preoperative clinical data of the three study groups. The WFG group had the highest attempted refractive error (for both sphere and cylinder). The SMILE group only included patients with refractive cylinder of 3.00 D or less. The proportion of eyes with refractive cylinder higher than 3.00 D was 8.4% (21 of 249) eyes in the TOPO group and 23.1% (77 of 334) in the WFG group.
Baseline Clinical Data and Demographics From Premarket Approval FDA Studies
Figure 1 shows the percentage of eyes with 20/20 or better UDVA over time. At 1 month, SMILE had slower visual recovery, with a lower percentage of eyes (65.8%) having 20/20 visual acuity compared to the TOPO (87.5%) and WFG (88.0%) groups (P < .01). At 6 months, there was no statistically significant difference between the three groups. At the 12-month visit, the WFG group showed a decrease in UDVA compared to the other groups (P < .01), but the difference in percentages between the SMILE and TOPO groups was not statistically significant (P = .16).
Uncorrected distance visual acuity (UDVA) over time. SMILE = small incision lenticule extraction; TOPO = topography-guided laser in situ keratomileusis (LASIK); WFG = wavefront-guided LASIK
Figure 2 presents cumulative UDVA for each group at 6 months. By this time point, each cohort had achieved refractive stability. The follow-up for the 6-month visit was also good, with 98.7% (300 of 304) of eyes in the SMILE group, 98.0% (244 of 249) of eyes in the TOPO group, and 100% (334 of 334) of eyes in the WFG group available for examination. Six-month postoperative outcomes showed no statistically significant difference for each level of presented visual acuity (20/20 to 20/40) between the three groups.
Six months postoperative cumulative uncorrected distance visual acuity. SMILE = small incision lenticule extraction; TOPO = topography-guided laser in situ keratomileusis (LASIK); WFG = wavefront-guided LASIK
In all three studies, the safety was evaluated as the loss of two or more lines of CDVA compared to baseline measurement between the 1- and 12-month visits. At 1 month, SMILE exhibited a slightly higher loss of CDVA, with 5 of 304 eyes (1.6%) having a loss of two or more lines compared to 0.4% and 0.3% in the TOPO and WFG groups, respectively. However, this difference was not statistically significant (P = .12). From 3 months on, the loss of CDVA was minimal in all three groups, with none or no more than 1 eye in each group having CDVA reduced by two or more lines.
Figure 3 depicts the percentage of eyes with MSE within ±0.50 D of plano at each follow-up visit. The SMILE and TOPO groups had comparable outcomes with no obvious change over the follow-up time, whereas the WFG group had significantly lower percentages of eyes within ±0.50 D of emmetropia and a reduction in percentages over the 12-month period, which was in agreement with the difference in preoperative attempted correction in each group.
Postoperative manifest spherical equivalent (MSE) over time: percentage of eyes within ±0.50 diopters (D) of emmetropia. SMILE = small incision lenticule extraction; TOPO = topography-guided laser in situ keratomileusis (LASIK); WFG = wavefront-guided LASIK
Figure 4 shows the stability of MSE over time. The SMILE and TOPO groups demonstrated stable results with minimal and clinically insignificant changes over the 12 months. The WFG group had a gradual regression from −0.33 ± 0.35 D at 1 month to −0.49 ± 0.04 D at 12 months with a slight undercorrection apparent at all examinations.
Stability of manifest spherical equivalent (MSE) over time. SMILE = small incision lenticule extraction; TOPO = topography-guided laser in situ keratomileusis (LASIK); WFG = wavefront-guided LASIK
The stability of MSE is further explored in Table 2 for 1 to 3 months and 3 to 6 months. Based on the paired comparison of eyes between the two consecutive examinations, the estimated yearly change in MSE was slightly hyperopic in the SMILE group, whereas both the TOPO and WFG groups showed a slight myopic regression, which was more obvious in the WFG group. For the WFG group, the refractive regression was the highest between 1 and 3 months (the refractive change between the two visits was equivalent to a yearly change of −0.576 D, compared to −0.030 D in the TOPO group and +0.185 D in the SMILE group).
Change in MSE
The stability of refractive cylinder (nonvector form) over time is shown in Figure 5. The SMILE and TOPO groups had comparable and stable refractive cylinder over the 12 months. The WFG group had generally higher residual cylinder, which is understandable considering the much higher attempted correction, but the change between 1 and 12 months was minimal in all three groups.
Stability of refractive cylinder over time. SMILE = small incision lenticule extraction; TOPO = topography-guided laser in situ keratomileusis (LASIK); WFG = wavefront-guided LASIK
Table 3 presents outcomes of vector analysis for comparable refractive cylinder groups between all three studies (preoperative refractive cylinder > 0.50 D to ≤ 1.00 D, > 1.00 D to ≤ 2.00 D, and > 2.00 to ≤ 3.00 D). Each of the categories had similar preoperative intended refractive correction (vector difference between the preoperative astigmatic correction vector and the target postoperative cylinder vector), although the TOPO group had slightly lower intended refractive correction in each refractive bin. The vector variables are presented for the 6-month postoperative visit in the SMILE and WFG groups, but the TOPO group presents astigmatic outcomes only for the 3-month postoperative visit.
Vector Analysis Comparison
Considering that the TOPO group achieved refractive stability at 3 months and there was no change in the mean refractive cylinder between 3 and 6 months (Figure 5), it is reasonable to assume the 3-month data are comparable to the 6-month data in the TOPO group.
The error vector is defined as the vector difference between the intended and the surgically induced refractive correction and it is equivalent to the magnitude of residual refractive cylinder in nonvector form. Unfortunately, this variable was not presented in the TOPO group. The error vector was less for the SMILE group in the lowest refractive bin (0.15 ± 0.30 D) compared to the WFG group (0.30 ± 0.23 D). For the remaining two refractive bins, the outcomes were comparable (Table 3).
The correction ratio (the ratio between surgically induced and intended refractive correction) was slightly greater than 1 in the SMILE and TOPO groups for the lowest refractive bin, indicating slight vector overcorrection of the refractive cylinder, whereas the WFG group had slight undercorrection. For the two remaining refractive bins (preoperative cylinder between 1.00 and 3.00 D), the correction ratio indicated undercorrection for all three groups.
The error ratio is defined as the proportion of the intended correction that was not successfully treated (|error vector|/|intended refractive correction|). There were considerable differences in error ratio in the lowest refractive bin, with SMILE having the lowest error ratio and WFG having the highest. However, the differences in error ratio in the remaining two refractive bins between all three groups were minimal.
Table 4 shows the comparison of axis shift (absolute of the difference between preoperative axis and postoperative axis in units of degree) between the three studies, according to the amount of residual cylinder. In the comparison, the TOPO group used slightly different inclusion criteria for refractive bins (Table 4). Merging all refractive bins, 68.0%, 42.4%, and 48.6% of SMILE, TOPO, and WFG eyes, respectively, had an axis shift within 5° (P < .01). There was a statistically significant difference between SMILE and TOPO and SMILE and WFG, but not between TOPO and WFG. The percentage of eyes with an absolute axis shift within 15° was 76.7% for the SMILE group, 51.0% for the TOPO group, and 64.8% for the WFG group (P < .01). With a post-hoc comparison, there was a statistically significant difference between each combination of the three groups.
Residual Astigmatic Error by Absolute Axis Shift
This study reviews the FDA PMA data of the three most recently approved laser vision correction strategies for myopia and myopic astigmatism. TOPO and WFG LASIK are customized forms of ablation; WFG treatment uses ocular wavefront aberrations to drive excimer laser ablation, whereas TOPO treatments are based on corneal topography and refractive error.4 Both techniques have demonstrated efficacy and safety, and superiority of one technique over the other is debatable because each technique has shown some advantages/disadvantages in patients with different corneal parameters, topographic irregularities, or higher order aberrations.4,6,11 SMILE is a relatively new method that has been available in clinical practice since 2011.12 It is an intrastromal procedure that involves the creation of a refractive lenticule that is subsequently mechanically removed through a small corneal incision without the use of an excimer laser. The theoretical advantages of this include better preservation of the anterior corneal stroma, thereby maintaining better corneal integrity, less induction of dry eye, and faster recovery of corneal sensitivity.13,14
In the current comparison, all three techniques showed good refractive stability with minimal fluctuation between 1 and 12 months postoperatively. Patients in the SMILE and TOPO groups had minimal differences in the mean MSE over time, as well as a higher percentage of patients within ±0.50 D of attempted correction. However, comparison of these two studies to the WFG group should be interpreted with caution because it had the highest attempted correction for both sphere and cylinder (up to 12.00 D of MSE and up to 8.00 D of refractive cylinder), which might have resulted in the higher amount of undercorrection and less refractive predictability in this study. The undercorrection was obvious from early postoperative visits, and a nomogram adjustment has been shown to improve refractive predictability.15–17
In terms of visual acuity, 6-month data (when all three procedures achieved refractive stability) do not show significant differences in UDVA. However, SMILE demonstrated slower visual recovery, apparent at the 1-month examination, whereas long-term UDVA in the WFG group was affected by refractive undercorrection. The loss of corrected visual acuity was also slightly higher at 1 month for SMILE compared to WFG and TOPO, but the difference was not statistically significant. At 12 months, all three procedures had minimal loss of CDVA.
Slower visual recovery with SMILE has previously been reported compared to flap-based refractive surgeries.13 Refinements in surgical technique in terms of optimization of scan modes18 and lowering energy levels.19–21 have led to some improvements in recovery times. Essentially, the two techniques differ in healing response. Initial microdistortions in Bowman's layer22,23 have been observed following SMILE, but stabilize after 1 week. Agca et al.24 reported increased backscatter light intensity on confocal microscopy, which was still statistically significant at 3 months in fellow-eye comparison between SMILE and femtosecond laser–assisted LASIK. More recently, Ganesh et al.25 highlighted the correlation between modular transfer function and interface healing/interface granularity following SMILE, which still affects some patients at 3 months postoperatively. Other factors such as surgical manipulation and corneal edema can also play a role in prolonged recovery.26 However, whenever SMILE and LASIK with a variety of platforms was compared in meta-analyisis,27–30 no statistically significant difference in UDVA and CDVA and refractive predictability was found for the final examination.
In terms of astigmatic correction, both the SMILE and TOPO groups showed comparable mean values over time with minimal and clinically insignificant changes between 1 and 12 months of follow-up. The WFG group had slight regression, but considering the higher attempted amount of cylinder treated in the study, the regression (0.05 D) between the 1- and 12-month visits was minimal.
There has been discussion in the literature about the potential inferiority of SMILE in astigmatic correction due to the lack of automated cyclorotation compensation and the centration being reliant on the surgeon and the patient's fixation, whereas the other two techniques (WFG and TOPO) use automated eye tracking. When comparing wavefront-guided ablation with the same platform (Visx STAR S4 IR) and SMILE, Khalifa et al.31 found significantly higher difference vector and angle of error and significantly lower correction index (variables defined by the Alpins method32) for astigmatic correction performed by SMILE. On the other hand, Zhang et al.33 found that WFG was better than SMILE in correction of moderate astigmatism, but for higher astigmatism, both procedures equally under-corrected refractive cylinder.
Comparing TOPO LASIK and SMILE, Kanellopoulos34 found that TOPO LASIK outperformed SMILE in most of the study variables, including astigmatic correction. This was a contralateral study, but the sample size was relatively small (22 eyes in each group). However, other studies compared astigmatic correction with the Allegretto laser35–37 (not specifying which algorithm was used for ablation) and SMILE; two reported no difference in astigmatic correction,35,36 whereas one study37 found less favorable outcomes of astigmatic correction with SMILE for low to moderate myopic astigmatism.
The three groups compared in this study complied with high standard requirements of FDA PMA studies and used the same vector analysis methodology. Although the groups differed in the preoperative clinical parameters, for the astigmatic correction, we selected only the comparable refractive bins (up to 3.00 D of refractive cylinder). Outcomes of this study show that SMILE was not inferior in astigmatic correction compared to the other two studies. In fact, all three procedures similarly undercorrected refractive cylinder for higher attempted corrections. The WFG group showed slightly less predictable astigmatic outcomes for the lowest refractive category.
Absolute axis shift was used for the comparison of preoperative to postoperative cylinder axis change. Interestingly, despite the lack of automated centration, SMILE had the highest percentage of eyes with axis shift within 5°. However, it would have been better to compare error of angle, which determines the change in axis based on vector components rather than an absolute change, but this variable was not presented in the TOPO and WFG groups.
The current study has a few limitations. As we have already discussed, the preoperative clinical variables were not comparable, and the WFG group had significantly higher preoperative refractive error. Statistical comparison of continuous variables (eg, the mean preoperative or postoperative refractive error) was not possible without access to the full dataset of each study. However, we believe that plotting outcomes of the three procedures over the 12-month period will help clinicians to see the overall trend in outcomes over time and determine whether the changes in refraction were significant from a clinical point of view. Other variables such as change in higher order aberrations or patient-reported outcomes would also be useful in comparison, but the three studies used considerably different questionnaires and changes in higher order aberrations were reported for different pupil sizes and measured with different devices.
Despite the limitations of this review, we can conclude that all three modern refractive corneal correction strategies were predictable and safe and significantly exceeded targets set by the FDA. All three techniques demonstrated excellent visual outcomes for the attempted correction presented in each cohort with no obvious superiority of one technique over the others in astigmatic correction.
- Stuart A. A look at LASIK past, present and future. https://www.aao.org/eyenet/article/look-at-lasik-past-present-future
- Solomon KD, Fernández de Castro LE, Sandoval HP, et al. Joint LASIK Study Task Force. LASIK world literature review: quality of life and patient satisfaction. Ophthalmology. 2009;116(4):691–701. doi:10.1016/j.ophtha.2008.12.037 [CrossRef]19344821
- Smadja D, Reggiani-Mello G, Santhiago MR, Krueger RR. Wavefront ablation profiles in refractive surgery: description, results, and limitations. J Refract Surg. 2012;28(3):224–232. doi:10.3928/1081597X-20120217-01 [CrossRef]22373035
- Chen LY, Manche EE. Comparison of femtosecond and excimer laser platforms available for corneal refractive surgery. Curr Opin Ophthalmol. 2016;27(4):316–322. doi:10.1097/ICU.0000000000000268 [CrossRef]27031540
- Moshirfar M, Shah TJ, Skanchy DF, Linn SH, Durrie DS. Meta-analysis of the FDA reports on patient-reported outcomes using the three latest platforms for LASIK. J Refract Surg. 2017;33(6):362–368. doi:10.3928/1081597X-20161221-02 [CrossRef]28586495
- Moshirfar M, Shah TJ, Skanchy DF, Linn SH, Kang P, Durrie DS. Comparison and analysis of FDA reported visual outcomes of the three latest platforms for LASIK: wavefront guided Visx iDesign, topography guided WaveLight Allegro Contoura, and topography guided Nidek EC-5000 CATz. Clin Ophthalmol. 2017;11:135–147. doi:10.2147/OPTH.S115270 [CrossRef]28115827
- U.S. Food and Drug Administration. Premarket Approval Study: VisuMax™ femtosecond laser lenticule removal procedure for the correction of myopia with or without astigmatism. https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfpma/pma.cfm?id=P150040S003
- U.S. Food and Drug Administration. Premarket Approval Study: Allegretto Wave Eye-q excimer laser system. https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfPMA/pma.cfm?id=P020050S012
- U.S. Food and Drug Administration. Premarket Approval Study: STAR S4 IR excimer laser system with IDesign Wavescan Studio System. https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfpma/pma.cfm?id=P930016S044
- Eydelman MB, Drum B, Holladay J, et al. Standardized analyses of correction of astigmatism by laser systems that reshape the cornea. J Refract Surg. 2006;22(1):81–95. doi:10.3928/1081-597X-20060101-16 [CrossRef]16447941
- Toda I, Ide T, Fukumoto T, Tsubota K. Visual outcomes after LASIK using topography-guided vs wavefront-guided customized ablation systems. J Refract Surg. 2016;32(11):727–732. doi:10.3928/1081597X-20160718-02 [CrossRef]27824375
- 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(3):335–339. doi:10.1136/bjo.2009.174284 [CrossRef]
- Reinstein DZ, Archer TJ, Gobbe M. Small incision lenticule extraction (SMILE) history, fundamentals of a new refractive surgery technique and clinical outcomes. Eye Vis (Lond). 2014;1(1):3. doi:10.1186/s40662-014-0003-1 [CrossRef]
- Damgaard IB, Reffat M, Hjortdal J. Review of corneal biomechanical properties following LASIK and SMILE for myopia and myopic astigmatism. Open Ophthalmol J. 2018;12(1):164–174. doi:10.2174/1874364101812010164 [CrossRef]30123381
- Schallhorn S, Brown M, Venter J, Teenan D, Hettinger K, Yamamoto H. Early clinical outcomes of wavefront-guided myopic LASIK treatments using a new-generation Hartmann-Shack aberrometer. J Refract Surg. 2014;30(1):14–21.
- Schallhorn SC, Venter JA, Hannan SJ, Hettinger KA. Outcomes of wavefront-guided laser in situ keratomileusis using a new-generation Hartmann-Shack aberrometer in patients with high myopia. J Cataract Refract Surg. 2015;41(9):1810–1819. doi:10.1016/j.jcrs.2015.10.007 [CrossRef]26603388
- Schallhorn SC, Venter JA, Hannan SJ, Hettinger KA. Wavefront-guided photorefractive keratectomy with the use of a new Hartmann-Shack aberrometer in patients with myopia and compound myopic astigmatism. J Ophthalmol. 2015;2015:514837. doi:26504595
- Shah R, Shah S. Effect of scanning patterns on the results of femtosecond laser lenticule extraction refractive surgery. J Cataract Refract Surg. 2011;37(9):1636–1647. doi:10.1016/j.jcrs.2011.03.056 [CrossRef]21855763
- Donate D, Thaëron R. Lower energy levels improve visual recovery in small incision lenticule extraction (SMILE). J Refract Surg. 2016;32(9):636–642. doi:10.3928/1081597X-20160602-01 [CrossRef]27598734
- Ji YW, Kim M, Kang DSY, et al. Lower laser energy levels lead to better visual recovery after small-incision lenticule extraction: prospective randomized clinical trial. Am J Ophthalmol. 2017;179:159–170. doi:10.1016/j.ajo.2017.05.005 [CrossRef]28499707
- Li L, Schallhorn JM, Ma J, Cui T, Wang Y. Energy setting and visual outcomes in SMILE: a retrospective cohort study. J Refract Surg. 2018;34(1):11–16. doi:10.3928/1081597X-20171115-01 [CrossRef]29315436
- Luo J, Yao P, Li M, et al. Quantitative analysis of microdistortions in Bowman's layer using optical coherence tomography after SMILE among different myopic corrections. J Refract Surg. 2015;31(2):104–109. doi:10.3928/1081597X-20150122-05 [CrossRef]25735043
- Yao P, Zhao J, Li M, Shen Y, Dong Z, Zhou X. Microdistortions in Bowman's layer following femtosecond laser small incision lenticule extraction observed by Fourier-domain OCT. J Refract Surg. 2013;29(10):668–674. doi:10.3928/1081597X-20130806-01 [CrossRef]23938095
- 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;2014:265012. doi:24734168
- Ganesh S, Brar S, Pandey R, Pawar A. Interface healing and its correlation with visual recovery and quality of vision following small incision lenticule extraction. Indian J Ophthalmol. 2018;66(2):212–218.29380760
- Agca A, Demirok A, Yildirim Y, et al. Refractive lenticule extraction (ReLEx) through a small incision (SMILE) for correction of myopia and myopic astigmatism: current perspectives. Clin Ophthalmol. 2016;10:1905–1912. doi:10.2147/OPTH.S80412 [CrossRef]27757010
- Yan H, Gong LY, Huang W, Peng YL. Clinical outcomes of small incision lenticule extraction versus femtosecond laser-assisted LASIK for myopia: a meta-analysis. Int J Ophthalmol. 2017;10(9):1436–1445.28944205
- Zhang Y, Shen Q, Jia Y, Zhou D, Zhou J. Clinical outcomes of SMILE and FS-LASIK Used to treat myopia: a meta-analysis. J Refract Surg. 2016;32(4):256–265. doi:10.3928/1081597X-20151111-06 [CrossRef]27070233
- Lee JK, Chuck RS, Park CY. Femtosecond laser refractive surgery: small-incision lenticule extraction vs. femtosecond laser-assisted LASIK. Curr Opin Ophthalmol. 2015;26(4):260–264. doi:10.1097/ICU.0000000000000158 [CrossRef]26058022
- Shen Z, Shi K, Yu Y, Yu X, Lin Y, Yao K. Small incision lenticule extraction (SMILE) versus femtosecond laser-assisted in situ keratomileusis (FS-LASIK) for myopia: a systematic review and meta-analysis. PLoS One. 2016;11(7):e0158176. doi:10.1371/journal.pone.0158176 [CrossRef]27367803
- Khalifa MA, Ghoneim AM, Shaheen MS, Piñero DP. Vector analysis of astigmatic changes after small-incision lenticule extraction and wavefront-guided laser in situ keratomileusis. J Cataract Refract Surg. 2017;43(6):819–824. doi:10.1016/j.jcrs.2017.03.033 [CrossRef]28732617
- Alpins N. Astigmatism analysis by the Alpins method. J Cataract Refract Surg. 2001;27(1):31–49. doi:10.1016/S0886-3350(00)00798-7 [CrossRef]11165856
- Zhang J, Wang Y, Chen X. Comparison of moderate- to high-astigmatism corrections using wavefront-guided laser in situ keratomileusis and small-incision lenticule extraction. Cornea. 2016;35(4):523–530. doi:10.1097/ICO.0000000000000782 [CrossRef]26890662
- Kanellopoulos AJ. Topography-guided LASIK versus small incision lenticule extraction (SMILE) for myopia and myopic astigmatism: a randomized, prospective, contralateral eye study. J Refract Surg. 2017;33(5):306–312. doi:10.3928/1081597X-20170221-01 [CrossRef]28486721
- Liu M, Chen Y, Wang D, et al. Clinical outcomes after SMILE and femtosecond laser-assisted LASIK for myopia and myopic astigmatism: a prospective randomized comparative study. Cornea. 2016;35(2):210–216. doi:10.1097/ICO.0000000000000707 [CrossRef]
- Chan TCY, Wang Y, Ng ALK, et al. Vector analysis of high (≥3 diopters) astigmatism correction using small-incision lenticule extraction and laser in situ keratomileusis. J Cataract Refract Surg. 2018;44(7):802–810. doi:10.1016/j.jcrs.2018.04.038 [CrossRef]29909252
- Chan TC, Ng AL, Cheng GP, et al. Vector analysis of astigmatic correction after small-incision lenticule extraction and femto-second-assisted LASIK for low to moderate myopic astigmatism. Br J Ophthalmol. 2016;100(4):553–559. doi:10.1136/bjophthalmol-2015-307238 [CrossRef]
Baseline Clinical Data and Demographics From Premarket Approval FDA Studies
|No. of eyes (patients)||304 (304)||249 (212)||334 (170)|
|Gender, no. (%)|
| Male||128 (42.1%)||93 (43.9%)||93 (54.7%)|
| Female||176 (57.9%)||119 (56.1%)||77 (45.3%)|
|Surgical eye, no. (%)|
| Right||139 (45.7%)||128 (51.4%)||–|
| Left||165 (54.3%)||121 (48.6%)||–|
|Age [years], mean ± SD (range)||33.2 ± 7.3 (22 to 58)||34.0 ± 9.3 (18 to 65)||32.3 ± 8.31 (18 to 58)|
|Preoperative sphere [D], mean ± SD (range)||−4.62 ± 2.32 (−1.00 to −10.00)||−4.01 ± 2.57 (X to −9.00)a||−5.32 ± 2.97 (X to −12.00)a|
|Preoperative cylinder [D], mean ± SD (range)||−1.53 ± 0.70 (−0.75 to −3.00)||−1.19 ± 1.23 (0.00 to −6.00)a||−1.77 ± 1.65 (0.00 to −8.00)a|
|Preoperative manifest spherical equivalent [D], mean ± SD (range)||−5.39 ± 2.30 (−1.50 to −10.88)||−4.61 ± 2.43 (X to −9.00)a||−6.21 ± 2.78 (X to −12.00)a|
Change in MSE
|1 to 3 months|
| Change in MSE ⩽ 1.00 D, no. of eyes (%) [CI]||303/304 (99.7%) [98.2, 100.0]||246/247 (99.60%) [98.8, 100.0]||332/334 (99.4%) [N/A]|
| Change in MSE ⩽ 0.50 D, no. of eyes (%) [CI]||292/304 (96.1%) [93.2, 97.9]||237/247 (95.95%) [93.5, 98.4]||N/A|
|Mean change of MSE [D], mean ± SD [CI]||0.031 ± 0.259 [0.002, 0.060]||−0.005 ± 0.07 [−0.04, 0.03]||−0.096 ± 0.293 [N/A]|
| Mean change per year [D]||0.185||−0.030||−0.576|
|3 month to 6 months|
| Change in MSE ⩽ 1.00 D, no. of eyes (%) [CI]||300/300 (100.0%) [98.8, 100.0]||243/243 (100.0%) [100.0, 100.0]||331/334 (99.1%) [N/A]|
| Change in MSE ⩽ 0.50 D, no. of eyes (%) [CI]||289/300 (96.3%) [93.5, 98.2]||235/243 (96.71%) [94.5, 99.0]||N/A|
| Mean change of MSE [D], mean ± SD [CI]||0.010 ± 0.219 [−0.015, 0.035]||−0.043 ± 0.06 [−0.08, −0.01]||−0.030 ± 0.321 [N/A]|
| Mean change per year [D]||0.038||−0.173||−0.120|
Vector Analysis Comparison
|Preoperative Cylinder Refractive Bin (D)||SMILE (6 Months)||TOPO (3 Months)||WFG (6 Months)|
|No. of eyes|
| > 0.50 to ⩽ 1.00||120||45||54|
| > 1.00 to ⩽ 2.00||108||43||54|
| > 2.00 to ⩽ 3.00||72||29||44|
|IRC vs SIRC|
| > 0.50 to ⩽ 1.00||0.88 ± 0.13; 0.92 ± 0.24||0.73 ± 0.10; 0.74 ± 0.18||0.86 ± 0.13; 0.81 ± 0.25|
| > 1.00 to ⩽ 2.00||1.54 ± 0.28; 1.44 ± 0.37||1.45 ± 0.30; 1.35 ± 0.38||1.61 ± 0.31; 1.57 ± 0.39|
| > 2.00 to ⩽ 3.00||2.58 ± 0.28; 2.31 ± 0.43||2.30 ± 0.27; 2.15 ± 0.43||2.54 ± 0.26; 2.31 ± 0.38|
|CR = SIRC / IRC|
| > 0.50 to ⩽ 1.00||1.05 ± 0.27||1.02 ± 0.25||0.95 ± 0.29|
| > 1.00 to ⩽ 2.00||0.94 ± 0.17||0.93 ± 0.18||0.98 ± 0.17|
| > 2.00 to ⩽ 3.00||0.89 ± 0.14||0.93 ± 0.15||0.91 ± 0.11|
|EV = IRC – SIRC|
| > 0.50 to ⩽ 1.00||0.15 ± 0.30||N/A||0.30 ± 0.23|
| > 1.00 to ⩽ 2.00||0.22 ± 0.31||N/A||0.23 ± 0.22|
| > 2.00 to ⩽ 3.00||0.34 ± 0.38||N/A||0.34 ± 0.30|
|ER = EV / IRC|
| > 0.50 to ⩽ 1.00||0.17 ± 0.38||0.21 ± 0.42||0.36 ± 0.28|
| > 1.00 to ⩽ 2.00||0.15 ± 0.21||0.14 ± 0.20||0.14 ± 0.15|
| > 2.00 to ⩽ 3.00||0.13 ± 0.16||0.17 ± 0.21||0.13 ± 0.12|
Residual Astigmatic Error by Absolute Axis Shift
|Residual Cylinder Magnitude (D)||Axis Shift|
|0°||> 0° to ⩽ 5°||> 5° to ⩽ 15°||> 15°|
|SMILE, 6 months (300 eyes)|
| 0.00||184 (61.3%)||0 (0%)||0 (0%)||0 (0%)|
| > 0.00 to ⩽ 0.50||0 (0%)||13 (4.3%)||15 (5%)||51 (17%)|
| > 0.50 to ⩽ 1.00||0 (0%)||6 (2%)||7 (2.3%)||16 (5.3%)|
| > 1.00 to ⩽ 2.00||0 (0%)||1 (0.3%)||4 (1.3%)||3 (1%)|
| > 2.00 to ⩽ 3.00||0 (0%)||0 (0%)||0 (0%)||0 (0%)|
| Total||184 (61.3%)||20 (6.7%)||26 (8.7%)||70 (23.3%)|
|TOPO, 3 months (210 eyes)|
| 0.00||77 (36.7%)||0 (0%)||0 (0%)||0 (0%)|
| > 0.00 to < 0.50||0 (0%)||9 (4.3%)||10 (4.8%)||73 (34.8%)|
| ⩾ 0.50 to < 1.00||0 (0%)||2 (1%)||6 (2.9%)||24 (11.4%)|
| ⩾ 1.00 to < 2.00||0 (0%)||1 (0.5%)||2 (1%)||6 (2.9%)|
| ⩾ 2.00 to < 3.00||0 (0%)||0 (0%)||0 (0%)||0 (0%)|
| Total||77 (36.7%)||12 (5.7%)||18 (8.6%)||103 (49%)|
|WFG, 6 months (247 eyes)|
| 0.00||78 (31.6%)||0 (0%)||0 (0%)||0 (0%)|
| > 0.00 to ⩽ 0.50||6 (2.4%)||24 (9.7%)||29 (11.7%)||75 (30.4%)|
| > 0.50 to ⩽ 1.00||0 (0%)||7 (2.8%)||8 (3.2%)||8 (3.2%)|
| > 1.00 to ⩽ 2.00||0 (0%)||5 (2%)||3 (1.2%)||2 (0.8%)|
| > 2.00 to ⩽ 3.00||0 (0%)||0 (0%)||0 (0%)||2 (0.8%)|
| Total||84 (34%)||36 (14.6%)||40 (16.2%)||87 (35.2%)|