Small incision lenticule extraction (SMILE) in the correction of myopic astigmatism: outcomes and limitations - an update

Effective optical zone following small incision lenticule extraction: a review

Small incision lenticule extraction (SMILE) is a "flapless" keratorefractive surgery with excellent safety, efficacy, stability, and predictability for myopia correction. A recent global multicenter study also reported good refractive outcomes for hyperopic SMILE. SMILE has shown advantages including improved biomechanical strength, fewer dry eye symptoms, less corneal denervation, and fewer surgery-induced higher-order aberrations over laser in situ keratomileusis (LASIK). However, night vision complaints, including glare, halos, and starbursts, could still occur after SMILE. These symptoms have been proven to be closely related to the effective optical zone (EOZ), which is defined as the achieved area of corneal ablation. A larger postoperative EOZ may indicate better visual quality, making EOZ an important safety parameter for keratorefractive surgeries. As SMILE has gained wider application globally, the EOZ following SMILE has also been increasingly studied in the field of refractive surgery. This review provides an update on topics related to the EOZ after SMILE, including its measurement and influencing factors, aiming to benefit the personalization of the surgical algorithm and ultimately improve the visual quality after the SMILE procedure.

Effect of Cyclotorsion Compensation in Small Incision Lenticule Extraction Surgery for the Correction of Myopic Astigmatism: A Systematic Review and Meta-Analysis

INTRODUCTION

Small incision lenticule extraction (SMILE) has made notable advancements in addressing myopic astigmatism. Nevertheless, the potential impact of cyclotorsion on surgical outcomes cannot be overlooked. This study aims to assess the effectiveness of cyclotorsion compensation technology in SMILE surgery for the correction of myopic astigmatism, examining its influence on postoperative visual quality.

METHODS

A systematic review and meta-analysis were conducted. A comprehensive literature search was performed using databases, including PubMed, Web of Science, EMBASE, Cochrane Library, EBSCO, Scopus, CNKI, VIP, and Wan Fang. Studies meeting the criteria were selected and included. Data were independently extracted by three authors. Clinical outcome parameters were analyzed using Review Manager version 5.3.

RESULTS

This meta-analysis included ten studies. The results showed that, compared with the control group (cyclotorsion compensation was not performed in SMILE), the following indicators in the cyclotorsion compensation group were: residual astigmatism (RA) [weighted mean difference (MD) = 0.73, 95% confidence interval (CI) + 0.26 to + 1.19, P = 0.002], spherical equivalent (SE) (MD = 1.99, 95% CI + 0.77 to + 3.21, P = 0.001), coma (MD = -0.06, 95% CI -0.08 to -0.04, P < 0.00001), higher-order aberrations (HOAs) (MD = -0.04, 95% CI -0.06 to -0.02, P < 0.0001), follow-up 6-month angle of error (AE) (MD = -2.67, 95% CI -3.71 to -1.63, P < 0.00001), and follow-up 6-month uncorrected distance visual acuity (UDVA) (MD = -0.05, 95% CI -0.08 to -0.01, P = 0.005), and the differences in results were statistically significant. However, the differences among correction index, index of success (IOS), targeted induced astigmatism (TIA), magnitude of error (ME), and spherical aberration (SA) were not statistically significant.

CONCLUSION

Cyclotorsion compensation proves to be effective and predictable for correcting myopic astigmatism. The cyclotorsion compensation group demonstrated advantages over the control group in terms of postoperative residual astigmatism, and it induced fewer coma aberrations. Whether cyclotorsion compensation can lead to better visual quality remains to be seen, and further research on correcting myopic astigmatism through cyclotorsion compensation is warranted.

12-Month Outcomes of Small Incision Lenticule Extraction With Proper Head Positioning but No Reference Marking for the Correction of Astigmatism

PURPOSE

To investigate the 12-month outcomes of small incision lenticule extraction (SMILE) with proper head positioning but no reference marking for correcting astigmatism.

METHODS

This was a retrospective cohort study of 3,541 patients (5,953 eyes) who underwent SMILE between July 2010 and April 2021. Patient positioning on the treatment bed was meticulously done in every patient to avoid face turn, head tilt, and chin-up or chin-down posture. The corrected distance visual acuity (CDVA), uncorrected distance visual acuity (UDVA), manifest refraction, astigmatic outcomes, and adverse events were evaluated at 1, 3, and 12 months postoperatively.

RESULTS

The mean preoperative manifest spherical equivalent and manifest cylinder were -5.15 ± 2.24 diopters (D) (range: -0.13 to -12.88 D) and -1.00 ± 0.77 D (range: -0.25 and -6.00 D), respectively. Of all eyes, 88.4% and 98.6% had the spherical equivalent within ±0.50 and ±1.00 D of emmetropia at 12 months. The percentage of eyes with UDVA of 20/20 or better was 92.5%. Six eyes (0.1%) lost two or more lines of CDVA at the 12-month visit. The predictability of cylinder correction was excellent, with 88.1% within ±0.50 D and 98.9% within ± 1.00 D of astigmatism correction at 12 months. The mean correction index (CI) at 12 months was 1.09 ± 0.45 (range: 0.17 to 4.99), indicating a slight astigmatism overcorrection. The high cylinder group tended to have undercorrection with greater residual astigmatism, whereas the low cylinder group was likely to have overcorrection with lesser residual astigmatism (P < .001). No serious adverse events were observed.

CONCLUSIONS

SMILE with proper head positioning but no reference marking produces safe, efficient, predictable, and stable outcomes for astigmatism correction over a 12-month period. [J Refract Surg. 2023;39(10):683-692.].

Bibliometric and visualized analysis of myopic corneal refractive surgery research: from 1979 to 2022

Background

Myopic corneal refractive surgery is one of the most prevalent ophthalmic procedures for correcting ametropia. This study aimed to perform a bibliometric analysis of research in the field of corneal refractive surgery over the past 40 years in order to describe the current international status and to identify most influential factors, while highlighting research hotspots.

Methods

A bibliometric analysis based on the Web of Science Core Collection (WoSCC) was used to analyze the publication trends in research related to myopic corneal refractive surgery. VOSviewer v.1.6.10 was used to construct the knowledge map in order to visualize the publications, distribution of countries, international collaborations, author productivity, source journals, cited references, keywords, and research hotspots in this field.

Results

A total of 4,680 publications on myopic corneal refractive surgery published between 1979 and 2022 were retrieved. The United States has published the most papers, with Emory University contributing to the most citations. The Journal of Cataract and Refractive Surgery published the greatest number of articles, and the top 10 cited references mainly focused on outcomes and wound healing in refractive surgery. Previous research emphasized "radial keratotomy (RK)" and excimer laser-associated operation methods. The keywords containing femtosecond (FS) laser associated with "small incision lenticule extraction (SMILE)" and its "safety" had higher burst strength, indicating a shift of operation methods and coinciding with the global trends in refractive surgery. The document citation network was clustered into five groups: (1) outcomes of refractive surgery: (2) preoperative examinations for refractive surgery were as follows: (3) complications of myopic corneal refractive surgery; (4) corneal wound healing and cytobiology research related to photorefractive laser keratotomy; and (5) biomechanics of myopic corneal refractive surgery.

Conclusion

The bibliometric analysis in this study may provide scholars with valuable to information and help them better understand the global trends in myopic corneal refractive surgery research frontiers. Two stages of rapid development occurred around 1991 and 2013, shortly after the innovation of PRK and SMILE surgical techniques. The most cited articles mainly focused on corneal wound healing, clinical outcomes, ocular aberration, corneal ectasia, and corneal topography, representing the safety of the new techniques.

Prediction of Early Visual Outcome of Small-Incision Lenticule Extraction (SMILE) Based on Deep Learning

INTRODUCTION

Deep learning (DL) has been widely used to estimate clinical images. The objective of this project was to create DL models to predict the early postoperative visual acuity after small-incision lenticule extraction (SMILE) surgery.

METHODS

We enrolled three independent patient cohorts (a retrospective cohort and two prospective SMILE cohorts) who underwent the SMILE refractive correction procedure at two different refractive surgery centers from July to September 2022. The medical records and surgical videos were collected for further analysis. Based on the uncorrected visual acuity (UCVA) at 24 h postsurgery, the eyes were divided into two groups: those showing good recovery and those showing poor recovery. We then trained a DL model (Resnet50) to predict eyes with early postoperative visual acuity of patients in the retrospective cohort who had undergone SMILE surgery from surgical videos and subsequently validated the model's performance in the two prospective cohorts. Finally, Gradient-weighted Class Activation Mapping (Grad-CAM) was performed for interpretation of the model.

RESULTS

Among the 318 eyes (159 patients) enrolled in the study, 10,176 good quality femtosecond laser scanning images were obtained from the surgical videos. We observed that the developed DL model achieved a high accuracy of 96% for image prediction. The area under the curve (AUC) value of the DL model in the retrospective cohort was 0.962 and 0.998 in the training and validation datasets, respectively. The AUC values in two prospective cohorts were 0.959 and 0.936. At the video level, the trained machine learning (ML) model (XGBoost) also accurately distinguished patients with good or poor recovery. The AUC value of the ML model was 0.998 and 0.889 in the retrospective cohort (training and test datasets, respectively) and 1.000 and 0.984 in the two prospective cohorts. We also trained a DL model which can accurately distinguish suction loss (100%), black spots (85%), and opaque bubble layer (96%). The Grad-CAM heatmap indicated that our models can recognize the area of scanning and precisely identify intraoperative complications.

CONCLUSIONS

Our findings suggest that artificial intelligence (DL and ML model) can accurately predict the early postoperative visual acuity and intraoperative complications after SMILE surgery just using surgical videos or images, which may display a great importance for artificial intelligence in application of refractive surgeries.

The effects of programmed optical zones on achieved corneal refractive power with myopic astigmatism after small incision lenticule extraction (SMILE): a vector analysis

PURPOSE

To evaluate the effects of different programmed optical zones (POZs) on achieved corneal refractive power (CRP) with myopic astigmatism after small incision lenticule extraction (SMILE).

METHODS

In total, 113 patients (113 eyes) were included in this retrospective study. The eyes were divided into two groups according to POZ: group A (6.5, 6.6, and 6.7 mm, n = 59) and group B (6.8, 6.9, and 7.0 mm, n = 54). Fourier vector analysis was applied to evaluate the error values between the attempted and achieved corneal refractive power (CRP). Alpins vector analysis was used to calculate surgically induced astigmatism (SIA), difference vector (DV), magnitude of error (ME), and astigmatism correction index (ACI). Multivariate regression analysis was performed to assess potential factors associated with the error values.

RESULTS

The error values in the group with large POZ were closer to zero, and significantly associated with the POZ at 2 and 4 mm of the cornea (β =  - 0.50, 95% confidence interval [CI] [- 0.80, - 0.20]; β =  - 0.37, 95% CI [- 0.63, - 0.10], P < 0.05, respectively). For the correction of astigmatism, the values of SIA, ME, and ACI were lower in group B than in group A (P < 0.05). The fitting curves between TIA and SIA were y = 0.83x + 0.19 (R² = 0.84) and y = 1.05x + 0.04 (R² = 0.90), respectively.

CONCLUSIONS

Smaller POZs resulted in higher error values between the achieved- and attempted-CRP in the SMILE procedure, which should be considered when performing surgery.

Small Incision Lenticule Extraction (SMILE) Versus Laser Assisted Stromal In Situ Keratomileusis (LASIK) for Astigmatism Corrections: A Systematic Review and Meta-analysis

PURPOSE

To compare small incision lenticule extraction (SMILE) and laser assisted stromal in situ keratomileusis (LASIK) for astigmatism correction.

DESIGN

Systematic review and meta-analysis METHODS: We reviewed published studies comparing outcomes after LASIK and SMILE for astigmatism correction by querying PubMed, EMBASE, Cochrane, and Web of Science, with a cut-off date of September 3, 2022. We also compared the changes in visual acuity, refraction, and high-order aberrations between the surgeries. Astigmatism correction outcomes in the low-to-moderate group (less than or equal to -2.00 D) and high group (greater than -2.00 D) were evaluated using vector analysis. The Cochrane risk of bias tool in RevMan software was used for randomized studies (RCT), and Risk Of Bias In Nonrandomized Studies - of Interventions (ROBINS-I) was used for the nonrandomized studies (NRSs).

RESULTS

There were 17 studies (5 randomized studies and 12 cohort studies), including 1,985 eyes. A statistically significant difference was found in the correction index (mean difference [MD] = -0.02, 95% confidence interval [CI] = -0.04 to -0.01, P =0.01), although there was no significant difference in the index of success (MD = 0.01, 95% CI = -0.03 to 0.05, P =0.51), different vector (MD = 0.07, 95% CI = 0.00 to 0.13, P =0.04), and angle of error (MD = 0.56, 95% CI = -0.34 to 1.45, P =0.22) between SMILE and LASIK. However, for low-to-moderate astigmatism correction, SMILE exhibited a smaller correction index (MD = -0.08, 95% CI= -0.13 to -0.02, P =0.008) and a larger difference vector (MD = 0.18, 95% CI = 0.09 to 0.27, P <0.0001) than LASIK. There was no significant difference between the different procedures in visual acuity and refraction (spherical equivalent: MD = -0.04, 95% CI = -0.08 to 0.01, P =0.15) or high-order aberration (MD = -0.01, 95% CI = -0.07 to 0.04, P =0.67), except spherical aberration (MD = -0.12, 95% CI = -0.23 to -0.01, P =0.04). The risk of bias was moderate in most studies because of poor reporting of several bias domains for RCTs, and because of confounding and selective outcome reporting for NRSs.

CONCLUSIONS

When used to treat severe astigmatism, both SMILE and LASIK provide effective and predictable results and generally have equivalent outcomes. However, evidence reveals a tendency toward undercorrection in the SMILE groups for astigmatism correction. In addition, LASIK has a greater probability of causing postoperative spherical aberration.

Efficacy of small-incision lenticule extraction surgery in high astigmatism: A meta-analysis

Purpose

This study aimed to evaluate the efficacy of small-incision lenticule extraction (SMILE) in improving vision and visual quality and correcting astigmatism for the treatment of high astigmatism.

Methods

Eligible studies and studies comparing the efficacy of SMILE with femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK) or transepithelial photorefractive keratectomy (T-PRK) for high astigmatism (≥2.00 D) were identified in PubMed, Embase, and the Cochrane Central Register of Controlled Trials, searched from their inception to 29 May 2022. The references of all searched studies were checked as supplements. The risk of bias was evaluated for each eligible study. The literature was screened according to the inclusion and exclusion criteria, and relative data were extracted. Data were extracted and analyzed by ReviewManager 5.4. The primary outcome was post-operative uncorrected distance visual acuity (UDVA). The secondary outcomes included corneal aberrations and vector parameters. The weight mean difference (WMD) and their 95% confidence intervals (95% CI) were used to assess the strength of the association.

Results

A total of six studies including 380 astigmatism eyes were involved, with 211 high-astigmatism eyes and 31 low-astigmatism eyes undergoing SMILE surgery, 94 high-astigmatism eyes undergoing FS-LASIK surgery, and 44 high-astigmatism eyes undergoing T-PRK surgery. Compared with non-SMILE, SMILE induced more astigmatism (weighted mean difference [WMD] = -0.07, 95% CI [-0.12 to -0.02], P = 0.005) and fewer sphere aberrations (WMD = -0.12, 95% CI [-0.17 to -0.08], P < 0.00001). The post-operative UDVA, sphere, spherical equivalent (SE), and higher order aberrations in different surgeries were likewise equivalent. The difference vector and index of success were significantly higher, and the surgically induced astigmatism vector, correction index, and magnitude of error were significantly lower in SMILE.

Conclusion

This meta-analysis suggests that SMILE, FS-LASIK, and T-PRK show excellent efficacy, predictability, and safety for myopia. SMILE exhibited less astigmatism refraction predictability and less surgically induced spherical aberrations. There may be more under-correction in SMILE. More randomized, prospective, and large sample-sized studies are needed to confirm these conclusions in the long term.

Postoperative efficacy, safety, predictability, and visual quality of implantable collamer lens implantation versus small incision lenticule extraction in myopic eyes: a Meta-analysis

AIM

To compare the postoperative efficacy, safety, predictability, and visual quality of implantable collamer lens (ICL) implantation versus small incision lenticule extraction (SMILE) in myopia eyes.

METHODS

PubMed, EMBASE, Web of Science, Cochrane Library and several Chinese databases were searched at May 2021 to select relevant studies in comparison of clinical outcomes between ICL implantation and SMILE for myopia. The primary outcomes were efficacy, safety, and predictability. And the secondary outcomes were postoperative higher-order ocular aberrations (HOAs), modulation transfer function cutoff frequency (MTF), objective scatter index (OSI), contrast sensitivity and a quality of vision (QoV) questionnaire.

RESULTS

A total of 1036 eyes from 10 studies, of which 503 eyes underwent ICL implantation and 533 eyes underwent SMILE, were enrolled in this Meta-analysis. Pooled results revealed that ICL group had a better safety index and post-corrected distance visual acuity (CDVA) (P=0.007, <0.00001, respectively), and a lower percentage of eyes with a postoperative CDVA lost 1 line (P=0.007) than the SMILE group. No significant differences were found in comparison of the other primary outcomes. In the long-term follow-up (>6mo), ICL group had a lower total HOA, coma, and spherical aberration than SMILE group (P=0.003, <0.00001, 0.04). Yet higher trefoil was found in ICL group at 6mo after surgery (P=0.003). Additionally, ICL group also had a higher MTF value (P=0.02), and a higher contrast sensitivity score for spatial frequencies of 1.5, 6, and 12 cpds (P=0.02, 0.005, 0.02, respectively). And it also had a lower score of bothersome in QoV questionnaire than SMILE group (P=0.003).

CONCLUSION

ICL implantation and SMILE have similar and comparable outcomes in term of the efficacy and predictability for correcting high myopia. However, ICL group is relatively safer and also has better visual quality in comparison of SMILE group.

Vector analysis of moderate to high myopic astigmatism after small-incision lenticule extraction (SMILE): 12-month follow-up

PURPOSE

To evaluate the refractive outcomes of small-incision lenticule extraction (SMILE) surgery in moderate to high myopic astigmatism.

STUDY DESIGN

Prospective interventional case series.

METHODS

This study evaluated 111 eyes of 68 patients treated with femtosecond SMILE surgery for the correction of myopia and astigmatism. Inclusion criteria were myopia of - 0.5 D or more and astigmatism between - 1.0 D and -5.0 D. Refractive and visual measurements were obtained preoperatively, 1 and 12 month(s) postoperatively. Vector analysis was used to study the astigmatic outcomes at 12-month follow-up. Comparison of results in two groups of patients with astigmatism below and over 3.00 D was performed.

RESULTS

The preoperative mean spherical equivalent was -5.48 ± 2.17 D (range - 1.75 to - 10.00 D) and the mean cylinder was -2.02 ± 1.09 D (range - 1.00 to - 5.00 D). The mean postoperative cylinder value was -0.60 ± 0.52 D at 12-month visit. The 12-month safety and efficacy indices were 0.98 ± 0.07 and 0.97 ± 0.12, respectively. The high astigmatism group showed significantly lower safety and efficacy indices. The postoperative residual astigmatism was 0.5 D or less in 73% of the eyes. Higher amount of residual astigmatism was observed in the high astigmatism group. The angle of error was ± 5 degrees in 49% and ± 15 degrees in 87% of the eyes.

CONCLUSION

SMILE surgery is effective and safe method for correcting myopic astigmatism. Vector analysis indicated a tendency for the under correction of astigmatism in subjects with high astigmatism.

Monson small-incision lenticule extraction fixation device

Small-incision lenticule extraction (SMILE) is a stromal based, flapless, minimally invasive form of laser vision correction for the treatment of myopia and myopic astigmatism. SMILE surgery is a more technical procedure compared with other refractive surgeries and generally has a longer skill mastery acquisition period. Thus far, no new stabilization devices or techniques have been proposed. To rectify this, a new distal corneal countertraction device for SMILE surgery, the Monson SMILE Fixation Device, is introduced. This device provides reliable corneal and globe stabilization during delamination and lenticular dissection. It may minimize tissue distortion and manipulation, simplify lenticule dissection, and may decrease operation times and improve cosmesis. Countertraction can also easily be adjusted throughout the procedure.

Comparison of refractive and visual outcomes between image-guided assisted small incision lenticule extraction and wavefront-optimized femtosecond laser in situ keratomileusis in treatment of high astigmatism

PURPOSE

To compare refractive and visual results of image-guided assisted small-incision lenticule extraction (IGA-SMILE) and wavefront-optimized femtosecond laser in situ keratomileusis (FS-LASIK) in the treatment of high astigmatism.

SETTINGS

Osmangazi Aritmi Hospital, Bursa, Turkey.

DESIGN

Retrospective.

METHODS

This retrospective case-matched study included 64 eyes that had undergone IGA-SMILE and 64 eyes that had undergone wavefront optimized FS-LASIK. The mean preoperative myopia and astigmatism were -4.05 ±1.98 diopter (D) and 3.11 ±1.06 D in the IGA-SMILE group and -4.21 ±2.23 D and -3.15 ±0.62 D in the FS-LASIK group. One year later, visual and refractive results were compared in the groups. Vector analysis based on Alpins method was done to evaluate astigmatic treatment.

RESULTS

At one year, the residual astigmatism was -0.21 ± 0.25 D in the IGA-SMILE and -0.21 ± 0.24 D in the FS-LASIK group (p=0.305). In the IGA-SMILE group, 57 (89.1%) eyes achieved uncorrected distance visual acuity (UDVA) of 20/20 or better, as did 56 (85.9%) eyes in the FS-LASIK group. Vector analysis results demonstrated that the difference vectors were 0.22 ±0.24 D and 0.21 ±0.22 D (p=0.230), the correction indexes were 0.95 ±0.08 and 0.95 ±0.08 (p=0.239), the indices of success were 0.08 ±0.09 and 0.08±0.09 (p=0.248), in the IGA-SMILE and the FS-LASIK groups, respectively.

CONCLUSION

The combination of an image-guided system with SMILE resulted in high efficacy and safety indices that were comparable to FS-LASIK surgery.

Corneal Stroma Thickness Changes after Myopic Laser Corneal Refractive Surgery

PURPOSE

To evaluate the postoperative behavior of the central corneal stroma thickness after myopic femto-LASIK and SMILE by using a combined anterior segment-OCT and placido disc topographer, and to compare the accuracy of both laser machines in predicting the real stromal change .

SETTING

Vissum Miranza, Alicante, Spain.

STUDY DESIGN

Prospective, observational, comparative study.

METHODS

The Visumax-500kHz femtosecond laser (FS), and the Amaris-750 excimer laser were used for the correction of myopia with or without myopic astigmatism. Central and paracentral stromal thicknesses (ST) and 6mm-corneal aberrometry were obtained with the MS39 topographer. Laser predicted stromal consumption was recorded (maximum lenticule thickness for SMILE and central ablation depth for LASIK). Visual and refractive outcomes were also evaluated. Total follow-up was 6 months.

RESULTS

77 LASIK-eyes were matched with 77 SMILE-eyes. Mean preoperative spherical equivalent (SE) was -3.92±1.67D for LASIK and -4.02±1.63D for SMILE;p=0.356. After LASIK, ST parameters showed a significant rethickening between months 1-3 (+4.38µm for central-ST;p<0.001), remaining stable thereafter. After SMILE, all ST parameters remained stable from month-1. Stromal ablation prediction was higher for SMILE compared to LASIK for all SE ranges, although postoperatively such differences were significant only for ametropias≤4D. At 6 months, mean SMILE laser prediction error was -13.21±7.00µm, while LASIK prediction showed better accuracy (+0.92± 8.16µm; p<0.001).

CONCLUSIONS

The accuracy of the Amaris-750 excimer laser in predicting the stromal consumption after LASIK was better than the VisuMax-FS laser for SMILE. While SMILE stromal thicknesses remained stable from month-1, after LASIK a mild stromal rethickening was observed up to the third month.

Functional Optical Zone and Visual Quality After Small-Incision Lenticule Extraction for High Myopic Astigmatism

Introduction

The aim of this study was to compare the functional optical zone (FOZ) after correction of high myopic astigmatism and low myopic astigmatism by small-incision lenticule extraction (SMILE).

Methods

In this prospective study, 30 patients who received SMILE for high myopic astigmatism correction (cylinderical diopters ≤ − 2.0D) were enrolled in the high astigmatism group (HA). The control group comprised 40 patients who underwent SMILE for low myopic astigmatism correction (LA; cylinderical diopters ≥ − 0.5D). FOZ was delineated as the area outlined by a change of 0.5D relative to the power at the corneal vertex on the total corneal refractive power map. An ellipse-fitting program (MatLab) was used to calculate some parameters of the FOZ. Visual quality evaluations were also conducted, including evaluations of wavefront aberrations, optical quality, and intraocular scattering, and completion of a quality of life questionnaire. All of the right eyes were analyzed in the study.

Results

The preoperative average treatment spherical equivalent (− 5.77 ± 1.86D vs. − 6.49 ± 1.49D; P = 0.074), lenticule thickness (120.87 ± 23.27 μm vs. 118.53 ± 21.66 μm; P = 0.666), and programmed optical zone (6.58 ± 0.17 mm vs. 6.65 ± 0.18 mm; P = 0.104) were comparable between the HA and LA groups. The long axes (6.99 ± 1.14 mm vs. 5.32 ± 0.61 mm; P < 0.001), short axes (4.66 ± 0.96 mm vs. 4.23 ± 0.64 mm; P = 0.047), and area (25.90 ± 8.03 mm² vs. 17.92 ± 4.36 mm²; P < 0.001) of the FOZ were significantly larger in the HA group than in the LA group. The centration of the FOZ were comparable between the two groups (0.62 ± 0.25 mm vs. 0.70 ± 0.25 mm; P = 0.194). Postoperative spherical aberration was lower in the HA group than in the LA group (0.07 ± 0.05 μm vs. 0.14 ± 0.10 μm; P = 0.001). There was no significant difference in the ocular scatter index (0.80 ± 0.46 vs. 0.73 ± 0.46; P = 0.447), modulated transfer function (MTF)_cutoff (37.89 ± 9.79 cpd vs. 39.78 ± 7.45 cpd; P = 0.363), and Strehl in two dimensions (Strehl2D) ratio (0.20 ± 0.04 vs. 0.20 ± 0.04; P = 0.363) between the HA group and the LA group. There were no significant differences in the scores on quality of life between the HA and LA groups (45.88 ± 2.15 vs. 45.64 ± 1.84; P = 0.423). Correlation analysis revealed that increase in the spherical aberration was significantly correlated with the long axes, short axes and area in the FOZ in both groups.

Conclusion

With a comparable optical design and attempted correction in SMILE, the eyes with higher myopic astigmatism correction achieved larger FOZ than the eyes with lower myopic astigmatism correction. Consequently, less spherical aberration induction was created after higher myopic astigmatism correction. This result may be associated with less corneal volume sculpted by laser for the higher astigmatism treatment, leading to fewer biochemical responses and les change in corneal aspherity. Good retinal image quality and satisfied quality of life were achieved at a comparable level in both study groups.

Early visual quality outcomes after small-incision lenticule extraction surgery for correcting high myopic astigmatism

Background

To evaluate early optical quality outcomes after small-incision lenticule extraction (SMILE) surgery for correcting high myopic astigmatism.

Methods

This retrospective study enrolled 55 eyes from 37 patients who had preoperative myopic astigmatism of ≥2.00 diopters (D) who had been treated with SMILE surgery. Preoperatively, the mean cylinder was − 2.41 ± 0.54 D (range, − 2.00 D to − 4.50 D). The preoperative and postoperative visual outcomes, refraction, and higher-order aberration (HOA) at 1 and 3 months were compared. Refractive astigmatism changes were analyzed by the Alpins vector method.

Results

Three months after SMILE surgery, the average cylinder was − 0.14 ± 0.31 D, and the average astigmatism vector was − 0.09 D × 6.34°. The angle of error (AofE) was limited to within ±10°, and the magnitude of error was limited to within ±1.0 D in all patients. The correction index (CI) was 0.98 ± 0.07, the index of success (IOS) was 0.08 ± 0.13, and the flattening index (FI) was 0.97 ± 0.07. Significant positive correlations were found between IOS and |AofE| (P = 0.000); negative correlations were found between FI and |AofE| (P = 0.000). The postoperative total HOA, spherical aberration, vertical coma aberration, and trefoil 30° were increased significantly compared with preoperative measurements, and the increase in HOA was closely related to preoperative astigmatism (P < 0.05).

Conclusions

SMILE has preferable outcomes for correcting high myopic astigmatism. Axis rotation during the surgery might influence the undercorrection of astigmatism. The increase of HOA after surgery is related to preoperative astigmatism.

Two-year outcomes after full-thickness astigmatic keratotomy combined with small-incision lenticule extraction for high astigmatism

Background

To evaluate clinical outcomes after full-thickness astigmatic keratotomy (FTAK) combined with small-incision lenticule extraction (SMILE) in eyes with high astigmatism.

Methods

This study comprised 75 eyes of 43 patients with over 4.0 diopters (D) of astigmatism who were treated with SMILE after FTAK. Visual acuities and refractive measurements were evaluated at 1 month after FTAK, and 1, 6, 12, and 24 months after SMILE. Vector analysis of the astigmatic changes was performed using the Alpins method.

Results

Twenty-four months after the combined procedure, the average spherical equivalent was reduced from − 6.56 ± 2.38 D to − 0.36 ± 0.42 D (p < 0.001). The uncorrected and corrected distance visual acuities improved from 1.54 ± 5.53 to − 0.02 ± 0.09 and from − 0.03 ± 0.07 D to − 0.07 ± 0.08 D (both p < 0.001), respectively. The preoperative mean astigmatism was − 5.48 ± 1.17 D, which was reduced to − 2.27 ± 0.97 D and − 0.34 ± 0.26 D at 1 month after FTAK and 24 months after SMILE, respectively (p < 0.001). The surgically-induced astigmatism after FTAK, SMILE, and FTAK and SMILE combined was 3.38 ± 1.18 D, 2.22 ± 0.84 D, and 5.39 ± 1.20 D, respectively. Furthermore, the correction index of FTAK, SMILE, and FTAK and SMILE combined was 0.63 ± 0.17, 0.90 ± 0.40, and 0.98 ± 0.06, respectively. There were no intraoperative or postoperative complications.

Conclusion

Our surgical procedure combining FTAK and SMILE showed good and stable clinical outcomes during two-year follow-up for the treatment of high astigmatism.

Influence of age on small incision lenticule extraction outcomes

PURPOSE

To evaluate the influence of patient's age at the time of surgery on small incision lenticule extraction (SMILE) refractive outcomes.

METHODS

This is a retrospective, consecutive, comparative study. We compared the refractive outcomes after myopic SMILE from two groups of patients divided by age (patients ≤35 and ≥40 years old). All eyes were evaluated preoperatively and at 1 and 6 months postoperatively. Main outcome measures were differences on efficacy, safety, predictability and astigmatic changes by vector analysis with ASSORT software between both study groups.

RESULTS

102 matched eyes of 53 patients were included. Preoperatively, we evidenced no differences in the mean SE or astigmatism between groups. However, 6 months postoperatively we observed a significantly worse mean astigmatism (p=0.019), while not regarding SE, in the older population, with a trend towards undercorrection of the refractive cylinder in the ≥40 group. We also observed a statistically significant difference in the efficacy (0.86-1 month and 0.97-6 months in ≥40group vs 0.97-1 month and 1.07-6 months in the ≤35 group; p=0.003) and safety indexes (0.93-1 month and 1.04-6 months in ≥40 group vs 1.0-1 month and 1.11-6 months in the ≤35 group; p=0.008) at 6 months among groups.

CONCLUSIONS

Post-SMILE refractive outcomes in those patients over 40 years of age, although acceptable, are not as good as those obtained in younger patients, showing a significantly lower efficacy and safety indexes, and poorer astigmatic outcomes, with a tendency towards undercorrection. We hypothetise that the increased corneal stroma stiffness in the aged group modifies the post-SMILE corneal stroma remodelling capacity, thus affecting the SMILE refractive and visual response.

Short and long term outcomes after small-incision lenticule extraction: A tertiary referral centre experience

PURPOSE

The objective of this study is to evaluate the preoperative and short- and long-term postoperative results in terms of visual acuity, refractive error, and corneal wavefront aberrations in patients with myopia and myopic astigmatism undergoing small incision lenticule extraction (SMILE).

METHODS

Seventy-nine eyes of 52 myopes with or without astigmatism (41 right and 38 left) were enrolled in this retrospective study. The measurements included uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), spherical equivalent (SE) and wavefront aberrations. All the measurements before and after SMILE surgery were systematically recorded.

RESULTS

Mean preoperative UDVA was 1.19±0.24 logMAR and improved to 0.06±0.17 logMAR at the 3-year postoperative follow-up. At the conclusion of the 3-year follow-up, UDVA was better than or equal to 20/20 and 20/25 in 73% and 84% of eyes, respectively. At 1 month postoperatively, CDVA was 0.05±0.23 logMAR and significantly lower than the preoperative CDVA, 0.02±0.04 log MAR (P>0.05). However, at 1 year and 3 years after surgery, CDVA showed a significant increase compared to preoperative CDVA. At the conclusion of the 3-year follow-up, SE was -0.47 D, and 69.6% and 83.5% of the eyes were within±0.50 D and±1.00 D, respectively, of the intended correction. HOA's, coma, and spherical aberration increased significantly. No significant change in trefoil was detected.

CONCLUSION

This study showed that SMILE produces a stable, safe outcome for surgical treatment of myopia and myopic astigmatism.

Vector analysis of small incision lenticule extraction and toric implantable collamer lens implantation for astigmatism correction

OBJECTIVES

To compare the efficacy of small incision lenticule extraction (SMILE) and toric implantable collamer lens (TICL) implantation for myopic astigmatism correction using vector analysis.

METHODS

In this retrospective study, 171 eyes of 171 patients with cylinder ⩾1.0 diopters (D) were recruited, with 97 eyes underwent SMILE and 74 eyes underwent TICL implantation. Preoperative and 3-months postoperative visual and refractive results were examined. The astigmatism correction, graded by the degree of preoperative cylinder was compared between two groups using vector analysis.

RESULTS

At 3-months postoperatively, the residual cylinder was -0.10 ± 0.21 D in the SMILE group and -0.30 ± 0.32 D in the TCL group (p < 0.05). Furthermore, 98% and 85% of eyes had the cylinder within ±0.5 D in the SMILE and TICL group, respectively. The vector analysis revealed similar target induced astigmatism vector in two groups. However, the difference vector, magnitude of error, angle of error, and index of success were significantly higher (0.30 ± 0.32 D, -0.19 ± 0.25, -2° ± 4.35°, and 0.16 ± 0.17 D, respectively) in the TICL group than the values in the SMILE group (0.10 ± 0.21 D, -0.05 ± 0.20, -0.03° ± 2.13°, and 0.05 ± 0.12, respectively), regardless of the degree of preoperative cylinder (all p < 0.05). For preoperative cylinder < 2.0 D, surgically induced astigmatism vector and correction index in the SMILE group were higher than those in the TICL group (p < 0.05).

CONCLUSION

Both SMILE and TICL implantation are effective techniques for myopic astigmatism correction. However, the accuracy of correction in the magnitude and axis of astigmatism with SMILE was better than that achieved with TICL implantation.

Astigmatism prediction in small-incision lenticule extraction

PURPOSE

To investigate whether postoperative-induced refractive astigmatism after small-incision lenticule extraction (SMILE) could be predicted by preoperative objective astigmatism measured with autorefraction, keratometry, and Scheimpflug tomography.

SETTING

University eye clinic.

DESIGN

Retrospective case series.

METHODS

Only eyes without preoperative subjective astigmatism treated with SMILE for myopia were included. Postoperative subjective astigmatism was compared with preoperative objective astigmatism. Examinations were performed before SMILE and 3 months postoperatively and included subjective refraction, keratometry, autorefraction, and Scheimpflug tomographer measurements. Astigmatism was analyzed using double-angle plots and multivariate statistics.

RESULTS

A total of 358 eyes of 358 patients were included. The mean preoperative sphere was -7.33 diopter (D) ± 1.46 (SD). The postoperative spherical equivalent was -0.30 ± 0.49 D. Postoperatively, 79.6% and 98.9% of patients had a subjective cylinder ≤0.50 D and ≤1.00 D, respectively. Preoperative objective astigmatism measured with keratometry, autorefraction, and Scheimpflug tomography was significantly different (P < .05) from postoperative subjective refraction when all patients were analyzed; for patients with postoperative refractive astigmatism ≥0.50 D, preoperative astigmatism with keratometry and Scheimpflug tomography was not significantly different from postoperative refractive astigmatism. Preoperative objective astigmatism ≥0.50 D increased the risk ratio of postoperative subjective astigmatism ≥0.50 D by 2.2 (P < .001).

CONCLUSIONS

Preoperative objective astigmatism could not be directly interchanged with postoperative subjective astigmatism, but the presence of preoperative astigmatism ≥0.50 D doubled the risk of inducing a postoperative subjective astigmatism ≥0.50 D. Extra care when performing subjective refraction should be taken in the presence of high objective astigmatism.

Small-Incision Lenticule Extraction (SMILE) for the Correction of Myopia with Astigmatism: Outcomes of the United States Food and Drug Administration Premarket Approval Clinical Trial

PURPOSE

To present outcomes of the United States Food and Drug Administration premarket approval clinical trial of small-incision lenticule extraction (SMILE) for the correction of myopia and astigmatism.

DESIGN

Prospective, multicenter clinical trial.

PARTICIPANTS

The study included 357 eyes of 357 patients treated with SMILE (50 for myopia and 307 for myopia with astigmatism). Preoperative sphere ranged between -1.00 and -10.00 diopters (D), with manifest spherical equivalent (MSE) of up to -11.50 D and refractive cylinder of up to -3.00 D.

METHODS

-Participants were followed up for 12 months. Corrected distance visual acuity (CDVA) and uncorrected distance visual acuity (UDVA), stability of the manifest refraction, and vector analysis of refractive cylinder are presented for the 307 eyes treated for myopia with astigmatism. Adverse events (AEs) are presented for all 357 eyes.

MAIN OUTCOME MEASURES

Corrected distance visual acuity, uncorrected distance visual acuity, manifest refraction, astigmatic outcomes, and adverse events.

RESULTS

Of the 307 astigmatic eyes enrolled in the study, 304 were treated successfully. In 3 eyes, the procedure was aborted because of intraoperative suction loss. The mean MSE reduced from -5.39±2.30 D at baseline to -0.01±0.24 D at 12 months. Of all eyes, 95.3% were within 0.50 D of emmetropia at 12 months. The percentage of eyes with UDVA of 20/20 or better was 89.0%. No loss of 2 or more lines of CDVA was observed at the 12-month visit. The refractive cylinder reduced from -1.53±0.70 D at baseline to -0.18±0.31 D at 12 months. The mean correction ratio of refractive cylinder was 0.96±0.16 and a slight undercorrection was apparent for higher attempted corrections of astigmatism. Three intraoperative AEs associated with difficult lenticule removal and resultant cap tear occurred, and all resolved without sequelae at postoperative day 1. During the postoperative period, 8 AEs were recorded, but none of them had significant consequences.

CONCLUSIONS

Small-incision lenticule extraction for the treatment of myopia and astigmatism was safe and effective, and the reported AEs had no significant impact on visual acuity. Slight undercorrection of refractive cylinder requires further attention.

Corneal refractive surgery combined with simultaneous corneal cross-linking: Indications, protocols and clinical outcomes-A review

Corneal refractive surgery is one of the most common approaches for correction of refractive errors. Combined corneal refractive surgery and corneal cross-linking (CXL) has been proposed as a method to achieve better refractive stability and to prevent iatrogenic corneal ectasia. However, there are concerns regarding its indications, surgical safety, standardization of protocols and long-term effect on corneal tissue. This review article aims to discuss the current knowledge and recent updates on combination of CXL and refractive surgery.

Comparison of Visual, Refractive and Ocular Surface Outcomes Between Small Incision Lenticule Extraction and Laser-Assisted In Situ Keratomileusis for Myopia and Myopic Astigmatism

Laser-assisted in situ keratomileusis (LASIK) is the most commonly performed laser refractive surgical technique worldwide for the treatment of myopia and myopic astigmatism. In recent years, small incision lenticule extraction (SMILE) has emerged as a promising alternative to LASIK, requiring only a single femtosecond laser to create an intrastromal lenticule, which is then removed via a small incision. The technique obviates the need for a corneal flap. A number of published studies have compared the two techniques in terms of visual, refractive and ocular surface outcomes. This review compares the clinical outcomes between LASIK and SMILE in treating myopia and myopic astigmatism based on studies published in the last 5 years. Twenty-two studies were included, all of which were observational in nature. Results suggest that the two techniques have comparable visual outcomes in terms of safety, efficacy and predictability, although recovery in visual acuity may be slower in SMILE-treated than LASIK-treated eyes. SMILE is found to result in less severe postoperative dry eye symptoms and faster recovery of corneal sensitivity than LASIK. It is important to note, however, that the SMILE technique is limited by the lack of a cyclotorsion-compensation system and option for customized treatment profile. The heterogeneity of results in this review may be attributable to the use of different LASIK platforms in different studies. Few studies compared the outcomes regarding severity of myopia. Future prospective randomized controlled trials with a larger sample size and longer follow-up period will be highly beneficial for progress in this field.

Astigmatism Correction Using SMILE

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.

Correction of Astigmatism With SMILE With Axis Alignment: 6-Month Results From 622 Eyes

PURPOSE

To evaluate postoperative clinical outcomes in myopic eyes with astigmatism that underwent femtosecond laser small incision lenticule extraction (SMILE) surgery with axis alignment.

METHODS

Overall, 622 eyes from 353 patients with myopia and astigmatism greater than -0.75 diopters (D) who had SMILE were included in this prospective study. Standard examinations were performed and visual acuity and vector astigmatism values were analyzed preoperatively and postoperatively.

RESULTS

Preoperative manifest spherical equivalent (SE) was -6.11 ± 1.68 D (range: -0.50 to -11.25 D) and manifest refractive cylinder was -1.60 ± 0.65 D (range: -0.75 to -6.25 D). In 622 enrolled eyes with astigmatism, 29.9% did not require rotation modification during surgery, and the average rotation degree (absolute) was 2.82° ± 1.44° (range: 0° to 10°). By 6 months after SMILE, all eyes showed improved uncorrected distance visual acuity (UDVA); approximately 96.8% of eyes with astigmatism achieved the same or better UDVA postoperatively compared to the preoperative corrected distance visual acuity (CDVA). Moreover, the cylinder of all eyes was within ±1.00 D, and 97% of eyes were within ±0.50 D. Only 47 eyes exhibited a low degree of astigmatism (range: -0.75 to 0.50 D). In patients with high astigmatism (>-3.00 D), the preoperative CDVA was -0.02 ± 0.11 logMAR and the 6-month postoperative UDVA was -0.01 ± 0.16 logMAR (n = 24, P > .05), further implying the effectiveness of modified SMILE for refractive correction in patients with astigmatism.

CONCLUSIONS

SMILE with axis alignment provides efficient, predictable, and safe refractive correction in patients with myopic astigmatism. [J Refract Surg. 2019;35(3):138-145.].

Initial Single-Site Surgical Experience with SMILE: A Comparison of Results to FDA SMILE, and the Earliest and Latest Generation of LASIK

Introduction

The primary objective was to show our initial surgical single-site experience with small incision lenticule extraction (SMILE) after the official enrollment in March 2017 following Food and Drug Administration (FDA) approval for simple myopia in late 2016 in the United States and, subsequently, compare our results to the earliest and most advanced generation of excimer platforms for laser-assisted in situ keratomileusis (LASIK) surgery.

Methods

This was a retrospective single-site study of 68 eyes from 35 patients who had SMILE surgery. The patients’ preoperative and postoperative uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), manifest sphere, manifest cylinder, intraoperative complications, and preoperative and postoperative visual symptoms were collected. We compared our findings to the results from the FDA SMILE study, and to the three earliest (1999–2000) and three of the most updated (2013–2016) platforms for LASIK.

Results

The cumulative UDVA was 20/20 and 20/40 or better in 74% and 100% of patients, respectively. The intended target refraction was within ± 0.5 and ± 1.00 D in 80% and 93% of cases, respectively. The prevalence of dry eyes decreased by nearly half from 1-week to the 6-month postoperative interval. Patients noted improvement in glare (17%), halos (17%), fluctuation (25%), and depth perception (8%) at the 6-month interval compared to preoperative levels.

Conclusions

This study’s findings are consistent with current SMILE reports. Notably, the results are superior to the earliest generation of LASIK, however inferior to the latest excimer platforms. SMILE does meet the efficacy and safety criteria met by FDA; however, there is a definite need for further improvement to reach the superior refractive outcomes produced by the latest generation of LASIK platforms.