Background:
Small incision lenticule extraction (SMILE) and femtosecond laser in situ keratomileusis (FS-LASIK) have been extensively studied as the main surgical methods for corneal refractive surgery. However, there is no consensus on whether SMILE is superior to FS-LASIK in corneal biomechanics. Therefore, this systematic review and meta-analysis used the results of ocular response analyzer and corvis ST to explore whether SMILE is superior to FS-LASIK in corneal biomechanics.
Methods:
The literature was searched in PubMed, EMBASE, and Controlled Trials Register databases. The Cochrane Collaboration’s “risk of bias” tool was used to evaluate the quality of the included randomized clinical trials, and the Newcastle-Ottawa Scale was used to evaluate the included non-randomized controlled trials. The results were analyzed using Revman 5.3.
Results:
Sixteen studies (3 randomized clinical trials and 13 non-randomized controlled trials) were included in this meta-analysis. There was no statistical difference in corneal biomechanics between SMILE and FS-LASIK in corneal hysteresis [mean difference (MD), 0.20; 95% confidence interval (CI): −0.09, 0.49; P = .18] and corneal resistant factor (MD, 0.31; 95% CI: −0.09, 0.71; P = .13), A1 time (MD, −0.02; 95% CI: −0.11, 0.07; P = .66), A1 length (MD, 0.01; 95% CI: −0.01, 0.03; P = .42), A1 velocity (MD, 0.00; 95% CI: −0.01, 0.01; P = .85), A2 velocity (MD, −0.01; 95% CI: −0.11, 0.09; P = .86), HC time (MD, 0.12; 95% CI: −0.13, 0.38; P = .35), The stiffness parameter at first applanation (MD, −7.91; 95% CI: −17.96, 2.14; P = .12), The ratio between the deformation amplitude 2 mm away from apex and the apical deformation (MD, 0.01; 95% CI: −0.26, 0.27; P = .96).
Conclusion:
A comprehensive assessment of the parameters of ocular response analyzer and corvis ST showed that SMILE is not superior to LASIK in corneal biomechanics 3 months post-surgery.
Keywords: corneal biomechanics, corvis ST (CST), femtosecond laser in situ keratomileusis (FS-LASIK), ocular response analyzer (ORA), small incision lenticule extraction (SMILE)
1. Introduction
Laser in situ keratomileusis (LASIK) and small incision lenticule extraction (SMILE) are one of the most common surgical procedures to correct refractive errors, and their safety, efficacy, and predictability have been well established.[1,2] Iatrogenic corneal ectasia is a rare complication after corneal refractive surgery. Although its prevalence is only 0.04% to 0.06%, it seriously threatens postoperative vision.[3]
Corneal biomechanical investigation plays an important role in identifying patients at high risk for developing iatrogenic ectasia after corneal refractive surgery. The ocular response analyzer (ORA) and the corvis ST (CST) are important devices for clinical corneal biomechanical assessment.[4]
This systematic review focused on the parameters of ORA or CST after SMILE or femtosecond laser in situ keratomileusis (FS-LASIK), and a meta-analysis was conducted to verify whether SMILE was superior to LASIK in terms of biomechanics.
The surgical procedure of FS-LASIK is as follows: first, a flap about 300° (360° minus hinge) is created using a femtosecond laser, subsequently the flap is lifted and the corneal tissue is removed using an excimer laser in the exposed stromal bed under the corneal flap. Finally, the corneal flap is replaced.
SMILE is a different surgical procedure performed using the 500 kHz VisuMax femtosecond laser (Carl Zeiss Meditec AG). The surgical procedure of SMILE is as follows: The VisuMax femtosecond laser creates a lenticule in the corneal stroma, and subsequently the lenticule is extracted via a 2 to 3-mm incision.
Both surgical procedures result in decreased corneal biomechanics which play an important role in the development of corneal ectasia.[5] Vertical ablation has a greater impact on corneal biomechanics than horizontal ablation, and the anterior 40% of central corneal stroma is the strongest part of the cornea.[6]SMILE does not involve creation of a flap, and the corneal stromal over the lenticule is untouched; therefore, SMILE has a better effect on biomechanics than LASIK.[7,8] However, there are numerous studies showing that there is no significant difference in the effects of SMILE and LASIK on corneal biomechanics.[9,10] Although there have been many previous studies on this issue, their conclusions are inconsistent.
ORA (Reichert Ophthalmics, Depew, NY) and CST (Oculus Optikgeräte GmbH, Wetzlar, Germany) are 2 commercially available devices used to measure corneal biomechanics.
With the development of surgical and examination equipment, this systematic review and meta-analysis can provide some new evidence on this issue using the outcomes of ORA and CST.
Both ORA and CST use air pulses to applanate the cornea - one as the cornea moves inward and the other as the cornea moves outward.
In ORA, the 2 pressures of the applanation are recorded as a representation of the corneal hysteresis (CH) and corneal resistant factor (CRF). CH reflects corneal viscosity, the ability to absorb and disperse energy. CRF indicates the overall resistance of the cornea, indicating its overall response to external forces. Both reflect the deformability of the cornea to air pulses.[11]
CST is a dynamic noncontact tonometer which can perform visual and quantitative observation of corneal deformation in response to air pulses within 100 ms using an ultra-fast Scheimpflug camera (4330 frames/seconds). Unlike ORA, CST can record corneal deformation data in real time to analyze corneal biomechanics.[12]
2. Methods
This meta-analysis was performed in accordance with the reporting guide of Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) (Moher et al 2009). There is no protocol for this meta-analysis.
2.1. Information source and search strategy
A literature search was conducted in PubMed, EMBASE, and Controlled Trials Register databases using the Search term “((((((((((Keratomileusis, Laser In Situ) OR (Laser-Assisted Stromal In Situ Keratomileusis)) OR (Laser Assisted Stromal In Situ Keratomileusis)) OR (Laser Intrastromal Keratomileusis)) OR (Intrastromal Keratomileuses, Laser)) OR (Intrastromal Keratomileusis, Laser)) OR (Laser Intrastromal Keratomileuses)) OR (Laser In Situ Keratomileusis)) OR (LASIK)) AND (((cornea refractive surgery) OR ((small incision lenticule extraction) OR (SMILE))) OR (refractive lenticule extraction))) AND (((((((ORA) OR (ocular response analyzer)) OR (covis ST)) OR (CST)) OR (covis)) OR (biomechanics)) OR (biomechanical)).” References of retrieved articles were also searched for additional relevant studies. The last search date was 24 June 2023.
All identified publications were independently screened by 2 reviewers. We reviewed titles, abstracts, and retrieved the full text that met the objectives of this meta-analysis. Disagreements over eligibility were resolved by reviewing the full text and discussing with Congling Zhao.
2.2. Eligibility criteria
All the included studies met the following criteria:
It was a randomized clinical trial (RCT) or a non-randomized controlled trial (non-RCT).
The study included at least 2 surgical procedures: SMILE and LASIK.
All patients had no history of corneal refractive surgery.
The study contained at least the parameters of ORA or Corvis ST.
Follow-up periods ranged from 3 to 12 months.
2.3. Data extraction
Two reviewers independently extracted data from the identified studies, including the following: first author, year of publication, study design, study location, follow-up time, number of eyes at baseline, age, spherical equivalent refraction, central corneal thickness, intraocular pressure before surgery, mean simulated keratometry, removed tissue thickness, optical zone and flap/cap thickness.
2.4. Qualitative assessment
The quality of the RCTs was assessed using the Cochrane Collaboration’s “risk of bias” tool, which included 6 items: random sequence generation, allocation concealment, blinding of participants and personnel, blinding of outcome assessment, incomplete outcome data, selective reporting, and other biases. Low, high, and unclear was assigned to each item, with a score ≥ 3 indicating high quality research. The Newcastle-Ottawa Scale, which included patient selection, comparability, and outcome assessments, was used to assess the risk for bias of non-RCT. A study can be awarded a maximum score of 1 for each numbered item within the selection (cohort studies: exposed cohort representative, nonexposed cohort selection, exposure ascertainment, outcome not present at start; case-control studies: adequate definition of cases, representativeness of the cases, selection of controls, definition of controls) and outcome (cohort studies: assessment, follow-up length, adequacy)/exposure(case-control studies: ascertainment of exposure, same method of ascertainment for cases and controls, nonresponse rate for cases and controls) categories. A maximum score of 2 can be given for comparability. The highest score is 9, with a score of ≥ 7 or above considered high quality research. When disagreements occurred, we contacted the authors of the studies for relevant information for accurate quality assessment.
2.5. Statistical analysis
Statistical analysis was performed using Review Manager (version 5.4; Cochrane Collaboration). Heterogeneity analysis was performed using the Cochrane I2 test. If I2 was ≤ 50%, indicating low or moderate heterogeneity, a fixed-effects model was used. If I2 was > 50%, indicating high heterogeneity, a random-effects model was used. Mean difference (MD) with 95% confidence interval (CI) was used to evaluate continuous outcomes. P < .05 was considered statistically significant. Sensitivity analyses were performed by excluding studies individually.
3. Results
3.1. Search results
Based on the search strategy, a total of 1162 studies were retrieved. After removing duplicate studies, a total of 298 studies were reviewed for eligibility. By reviewing the title, abstract and full text, a total of 16 studies were included in this meta-analysis. The screening process of the study is shown in Figure 1. The basic characteristics of the included studies are shown in Table 1. There were 788 patients in the SMILE group, and 761 patients in the LASIK group.
Figure 1.
PRISMA flow diagram of the literature search process.
Table 1.
Basic characteristics of included studies.
| First author | Year of publication | Study design | Study location | Follow-up time | Group | Number of eyes at baseline | Age (yr) | Spherical equivalent refraction (D) | CCT (um) | IOP (mm Hg) | Mean simulated keratometry | Removed tissue thickness | Optical zone | Flap/cap thickness |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Alper Agca | 2013 | RCT | Turkey | 6 | SMILE | 30 | 26.63 ± 4.57 | −3.62 ± 1.79 | 539 ± 28 | 44.46 ± 1.38 | 82.67 ± 19.85 | 6.5 | 120 | |
| FS-LASIK | 30 | 26.63 ± 4.57 | −3.71 ± 1.83 | 542 ± 37 | 44.56 ± 1.56 | 73.40 ± 24.18 | 6.5 | 120 | ||||||
| Bingjie Wang | 2016 | non-RCT | China | 12 | SMILE | 50 | 25.26 ± 6.64 | 7.60 ± 1.12 | 542.96 ± 23.34 | 14.68 ± 2.65 | 6.1–6.6 | 100–120 | ||
| FS-LASIK | 56 | 24.75 ± 6.24 | 7.68 ± 1.19 | 548.00 ± 23.97 | 14.94 ± 2.36 | 5.75–6.50 | 95 | |||||||
| Di Wu | 2014 | non-RCT | China | 6 | SMILE | 40 | 25.75 ± 5.40 | −5.71 ± 1.19 | 554.15 ± 24.77 | 44.31 ± 1.02 | 6 | 110 | ||
| FS-LASIK | 40 | 24.25 ± 6.02 | −5.80 ± 1.14 | 556.70 ± 30.60 | 43.96 ± 1.23 | 6 | 100–110 | |||||||
| Eman A Abd El-Fattah | 2020 | RCT | Egypt | 6 | SMILE | 30 | 26.4 ± 5.36 | −4.95 ± 1.32 | 556.8 ± 28.4 | 15.47 ± 1.845 | 55.82 ± 11.76 | 6.5 | 100 | |
| FS-LASIK | 30 | 27.65 ± 6.95 | −4.42 ± 1.45 | 555.35 ± 32.3 | 15.52 ± 2.023 | 57.42 ± 14.38 | 6.5 | 90 | ||||||
| Esraa El-Mayah | 2018 | non-RCT | Spain | 3 | SMILE | 30 | 29.53 ± 5.37 | −4.17 ± 1.86 | 7 | 110 | ||||
| FS-LASIK | 30 | 27.4 ± 4.95 | −3.97 ± 2.02 | 100 | ||||||||||
| Hassan Hashemi | 2023 | non-RCT | Iran | 12 | SMILE | 120 | 28.03 ± 5.26 | −4.66 ± 0.85 | 567.03 ± 25.32 | 18.17 ± 2.40 | −98.90 ± 20.87 | 6.5 | 120 | |
| FS-LASIK | 120 | 29.57 ± 4.89 | −4.47 ± 0.82 | 564.39 ± 27.52 | 17.29 ± 2.91 | −77.64 ± 20.79 | 6.5 | 110 | ||||||
| Iben Bach Pedersen | 2014 | non-RCT | Denmark | 12 | SMILE | 29 | 40.9 ± 1.25 | −7.10 ± 0.29 | 6.2 | 120 | ||||
| FS-LASIK | 35 | 38.4 ± 7.53 | −7.40 ± 0.20 | 6 | 110 | |||||||||
| Jun Zhang | 2016 | non-RCT | China | 3 | SMILE | 80 | 550.80 ± 25.77 | 6.43 ± 0.15 | 120 | |||||
| FS-LASIK | 80 | 547.06 ± 29.53 | 6.40 ± 0.17 | 100 | ||||||||||
| Kazutaka Kamiya | 2014 | RCT | Japan | 3 | SMILE | 24 | 31.8 ± 6.0 | −4.1 ± 1.7 | 543.1 ± 32.4 | 13.3 ± 3.2 | 6.5 | 120 | ||
| FS-LASIK | 24 | 31.8 ± 6.0 | −4.1 ± 1.7 | 545.5 ± 31.8 | 13.8 ± 3.3 | 6.5 | 120 | |||||||
| Lei Xia | 2016 | non-RCT | China | 6 | SMILE | 69 | 25.15 ± 4.42 | −5.04 ± 2.32 | 545.5 ± 28.2 | 6.0–6.5 | 120 | |||
| FS-LASIK | 59 | 23.65 ± 3.87 | −5.13 ± 1.36 | 538.8 ± 31.5 | 6.0–6.5 | 90–110 | ||||||||
| Mingna Liu | 2022 | non-RCT | China | 6 | SMILE | 45 | 25.17 ± 6.51 | −5.34 ± 1.02 | 544.71 ± 20.82 | 14.69 ± 2.44 | 6.5 | 120 | ||
| FS-LASIK | 45 | 28.28 ± 6.49 | −5.66 ± 1.59 | 543.18 ± 18.44 | 15.51 ± 2.46 | 6.2–6.5 | 110 | |||||||
| Mohamed Nagy | 2018 | non-RCT | Egypt | 12 | SMILE | 35 | 24.43 ± 5.91 | −8.05 ± 2.06 | 579.32 ± 10.65 | 43.57 ± 1.15 | ||||
| FS-LASIK | 38 | 23.84 ± 4.75 | −7.14 ± 1.97 | 578.96 ± 12.06 | 43.41 ± 1.08 | |||||||||
| Shervin Mir Mohi Sefat | 2015 | non-RCT | Germany | 3 | SMILE | 80 | 36.0 ± 7.8 | −4.83 ± 1.63 | 97.6 ± 24.0 | |||||
| FS-LASIK | 48 | 37.6 ± 6.6 | −3.23 ± 1.64 | 50.3 ± 21.1 | ||||||||||
| Wenjing Wu | 2015 | non-RCT | China | 3 | SMILE | 75 | 24.25 ± 5.38 | −5.49 ± 1.35 | 547.69 ± 27.06 | 15.80 ± 2.55 | 43.08 ± 1.25 | 6.0–6.1 | 110 | |
| FS-LASIK | 75 | 24.28 ± 5.24 | −5.56 ± 1.76 | 545.97 ± 27.71 | 15.79 ± 2.78 | 43.32 ± 1.22 | 6 | 100–110 | ||||||
| Yang Shen | 2014 | non-RCT | China | 3 | SMILE | 17 | 27.06 ± 6.77 | −6.48 ± 1.22 | 557.65 ± 22.56 | 100 | ||||
| FS-LASIK | 17 | 29.53 ± 7.42 | −8.71 ± 2.02 | 562.71 ± 20.96 | 90 | |||||||||
| Yue Xin | 2022 | non-RCT | China | 6 | SMILE | 34 | 25.7 ± 6.3 | −3.38 ± 0.72 | 546.6 ± 21.5 | 13.46 ± 1.93 | 6.68 ± 0.11 | 120.6 ± 3.4 | ||
| FS-LASIK | 34 | 26.4 ± 4.6 | −3.62 ± 0.87 | 545.0 ± 27.2 | 13.68 ± 1.69 | 6.79 ± 0.25 | 102.5 ± 4.7 |
CCT = central corneal thickness, FS-LASIK = femtosecond laser in situ keratomileusis, IOP = intraocular pressure, non-RCT = non-randomized controlled trial, RCT = randomized clinical trial, SMILE = small incision lenticule extraction.
3.2. Methodological quality evaluation
A total of 16 studies were included in this meta-analysis, and all studies were of high quality. There were 3 RCTs, whose quality assessment is shown in Figure 2, and 13 non-RCTs, whose quality assessment is shown in Table 2.
Figure 2.
The results of the methodological evaluation for RCT. RCT = randomized clinical trial.
Table 2.
NOS for non-RCT.
| Study | Selection | Comparability | Outcome/exposure | Sum of score |
|---|---|---|---|---|
| Bingjie Wang | 3 | 2 | 2 | 7 |
| Di Wu | 3 | 2 | 3 | 8 |
| Esraa El-Mayah | 3 | 2 | 3 | 8 |
| Hassan Hashemi | 3 | 2 | 3 | 8 |
| Iben Bach Pedersen | 3 | 2 | 2 | 7 |
| Jun Zhang | 3 | 2 | 3 | 8 |
| Lei Xia | 3 | 2 | 3 | 8 |
| Mingna Liu | 3 | 2 | 3 | 8 |
| Mohamed Nagy | 3 | 2 | 3 | 8 |
| Shervin Mir Mohi Sefat | 3 | 1 | 3 | 7 |
| Wenjing Wu | 3 | 2 | 2 | 7 |
| Yang Shen | 3 | 2 | 2 | 7 |
| Yue Xin | 3 | 2 | 3 | 8 |
Total NOS scores range from 0 (low quality) to 9 (high quality), with a maximum score of 4 for patient selection, 2 for comparison, and 3 for outcome/exposure.
non-RCT = non-randomized controlled trial.
3.3. ORA outcome
A total of 10 studies reported ORA outcomes comparing changes in corneal biomechanics after SMILE and FS-LASIK. No significant difference was found between SMILE and FS-LASIK in CH (MD, 0.20; 95% CI: −0.09, 0.49; P = .18; Ch I2 = 78, df = 9, I2 = 88%; Fig. 3) and CRF (MD, 0.31; 95% CI: −0.09, 0.71; P = .13; Ch I2 = 118.83, df = 9, I2 = 92%; Fig. 4). Heterogeneity I2 was >50%, so a random-effects model was used. Subgroup analysis according to follow-up time showed no statistical difference between the subgroups. Sensitivity analysis showed that the results were robust.
Figure 3.
Forest plots of the corneal biomechanics in CH. CH = corneal hysteresis.
Figure 4.
Forest plots of the corneal biomechanics in CRF. CRF = corneal resistant factor.
3.4. CST outcome
Although 8 studies reported the results of CST, there are many indicators evaluated by CST, and the indicators reported by each study differed. Therefore, this meta-analysis only analyzed the indicators reported by at least 3 studies. The difference between SMILE and FS-LASIK evaluated by CST was not significant in A1 time (MD, −0.02; 95% CI: −0.11, 0.07; P = .66; I2 = 73%; Fig. 5), A1 length (MD, 0.01; 95% CI: −0.01, 0.03; P = .42; I2 = 0%; Fig. 6), A1 velocity (MD, 0.00; 95% CI: −0.01, 0.01; P = .85; I2 = 0%; Fig. 7), A2 velocity (MD, −0.01; 95% CI: −0.11, 0.09; P = .86; I2 = 86%; Fig. 8), HC time (MD, 0.12; 95% CI: −0.13, 0.38; P = .35; I2 = 83%; Fig. 9), the stiffness parameter at first applanation (MD, −7.91; 95% CI: −17.96, 2.14; P = .12; I2 = 92%; Fig. 10), the ratio between the deformation amplitude 2 mm away from apex and the apical deformation (MD, 0.01; 95% CI: −0.26, 0.27; P = .96; I2 = 80%; Fig. 11). If I2 was ≤ 50%, a fixed-effects model was used. If I2 was > 50%, a random-effects model was used. After excluding studies individually, the results did not change significantly.
Figure 5.
Forest plots of the corneal biomechanics in A1 time.
Figure 6.
Forest plots of the corneal biomechanics in A1 length.
Figure 7.
Forest plots of the corneal biomechanics in A1 velocity.
Figure 8.
Forest plots of the corneal biomechanics in A2 velocity.
Figure 9.
Forest plots of the corneal biomechanics in HC time.
Figure 10.
Forest plots of the corneal biomechanics in SP-A1. SP-A1 = the stiffness parameter at first applanation.
Figure 11.
Forest plots of the corneal biomechanics in DA ratio-2 mm. DA ratio-2mm = the ratio between the deformation amplitude 2 mm away from apex and the apical deformation.
4. Discussion
In East and Southeast Asia populations, the prevalence of myopia in young adults is around 80% to 90%.[13] Corneal refractive surgery, especially SMILE and LASIK, is the main way to correct myopia. Extensive studies have shown that compared with LASIK, SMILE results in less iatrogenic dry eye, less corneal nerve damage, fewer induced higher-order aberrations and avoids corneal flap-related complications. [14–16]
However, there is no consensus on whether SMILE is superior to LASIK in corneal biomechanics. Seiler T et al[17] concluded that in axial 22-dimensional-strain-stress measurements, corneal biomechanical impairment after SMILE and LASIK was comparable. A 3-year follow-up study showed less CH and CRF changes after SMILE compared with FS-LASIK.[18] A meta-analysis of 19 studies conducted by Hui Guo et al[19] based on ORA results concluded that SMILE was biomechanically superior to LASIK. Although it included more studies, some of its included studies did not compare the biomechanical differences between SMILE and FS-LASIK, and only 2 to 5 of its included studies reported each parameter. Our meta-analysis had 3 to 10 studies to report each parameter and included more parameters, making the results more robust.
In this meta-analysis, there was no statistical difference between SMILE and FS-LASIK after 3 months of surgery in CH, CRF. A study conducted by Ihab Mohamed Osman et al[20] with only 1 month of follow-up found that the change after SMILE was significantly higher than that after LASIK in terms of the percentage of change in CH, CRF and the deformation amplitude. However, a study showed that the flap caused more weakening than the cap intraoperatively. Biomechanical differences between LASIK and SMILE eyes were similar after removal of tissue and ongoing wound healing.[21] The basic characteristics such as age, mean keratometry, intraocular pressure, and central corneal thickness were closely associated with corneal biomechanics.[22] Whether SMILE is superior to LASIK in biomechanics is a subject of debate, which may vary due to differences in the follow-up time, inspection instruments, and basic patient characteristics between studies.
Corneal biomechanics not only affects the progress of iatrogenic corneal ectasia, but also affects surgically induced corneal high-order aberrations.[23] Therefore, the study of corneal biomechanics plays an important role in the preoperative screening of the patients and optimization of postoperative visual quality.
Although previous studies have compared the corneal biomechanics after SMILE and LASIK, they were mainly based on ORA results and less dependent on CST. To the best of our knowledge, this is the first systematic review and meta-analysis which comprehensively assessed the parameters of ORA and CST, which can more strongly show that SMILE is not superior to LASIK in corneal biomechanics at 3 months post-surgery.
This meta-analysis has some limitations. On the 1 hand, the heterogeneity was high despite the subgroup analysis; however, the sensitivity analysis showed that the results were robust. On the other hand, studies on corneal biomechanical changes during surgery and within 3 months after surgery are lacking. Therefore, further research is needed to verify the changes in corneal biomechanics.
5. Conclusion
A comprehensive assessment of the parameters of ORA and CST showed that SMILE is not superior to LASIK in corneal biomechanics 3 months post-surgery.
Acknowledgments
We thank all of the participants recruited for this study.
Author contributions
Data curation: Songbai Chen, Congling Zhao.
Methodology: Congling Zhao.
Software: Hongjie Ma.
Supervision: Congling Zhao.
Writing – review & editing: Songbai Chen, Congling Zhaos.
Abbreviations:
- CH
- corneal hysteresis
- CI
- confidence interval
- CRF
- corneal resistant factor
- CST
- corvis ST
- FS-LASIK
- femtosecond laser in situ keratomileusis
- MD
- mean difference
- non-RCT
- non-randomized controlled trial
- ORA
- ocular response analyzer
- RCT
- randomized clinical trial
- SMILE
- small incision lenticule extraction
The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.
The authors have no funding and conflicts of interest to disclose.
How to cite this article: Chen S, Ma H, Zhao C. Corneal biomechanics after small incision lenticule extraction and femtosecond laser in situ keratomileusis: A systematic review and meta-analysis. Medicine 2023;102:32(e34580).
Contributor Information
Songbai Chen, Email: fll520191@163.com.
Hongjie Ma, Email: daihongbinyanke@163.com.
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