Small-incision lenticule extraction versus femtosecond lenticule extraction for myopic: a systematic review and Meta-analysis

Methodological quality of the review: Medium confidence

Author: Jia-Song Wang, Hua-Tao Xie, Ye Jia, Ming-Chang Zhang

Region: Japan, Turkey, Denmark, Singapore

Sector: Myopia

Subsector: Myopia treatment

Equity focus: No

Study population: Patients without history of ocular surgery and systemic disease

Type of programme: Hospital based

Review type: Other review

Quantitative synthesis method: Systematic review and meta-analysis

Qualitative synthesis method: Not applicable

Background: Myopia is the first most common eye disorder, which seriously affects more than 80% of Asian people. Refractive surgery is the most popular and effective treatment, especially in China. In recent years, refractive lenticule extraction (ReLEx) is a relatively new refractive procedure using the femtosecond laser for the correction of refractive errors. As we know, FLEx procedure is only rarely performed today. Maybe one of the reasons is that there is not a meta-analysis to compare the two surgical procedures; many surgeons think SMILE is better than FLEx.

Objectives: The objective of this study was to examine differences in efficacy, accuracy, safety, aberrations and corneal biomechanical between small incision lenticule extraction (SMILE) and femtosecond lenticule extraction (FLEx) for myopia.

Main findings: Seven trials published between 2013 to 2015 were adopted for final meta-analysis. Three RCTs and four non-randomised controlled trials in total contained 322 eyes with myopia. No significant differences were found in the efficacy [UDVA weighted mean difference (WMD) -0.01; 95% CI: -0.04 to 0.01; P=0.37, UDVA ≥20/20, OR 1.49; 95% CI: 0.78 to 2.86; P=0.23], accuracy (SE WMD -0.03; 95% CI: -0.12 to 0.07; P=0.58 , SE within ±0.5 D OR 1.25; 95% CI: 0.34 to 4.65; P=0.74), HOAs (WMD -0.04; 95% CI: -0.09 to 0.01; P=0.14) and CCT WMD 83; 95% CI: -7.07 to 10.72; P=0.69, CH WMD -0.01; 95% CI: -0.42 to 0.40; P=0.97, CRF WMD 0.17; 95% CI: -0.33 to 0.67; P=0.50) in the last follow-up. But for safety, FLEx may achieve fewer CDVA loss of two or more two lines (OR 11.11; 95 %CI: 1.27 to 96.86; P=0.03) than SMILE, however, CDVA (WMD 0.00; 95 %CI: -0.03 to 0.02; P=0.77) is similar.

Overall, authors found that SMILE and FLEx are comparable in terms of both efficacy, accuracy, aberrations and corneal biomechanical measures in the follow-up, but FLEx seems to be better in terms of safety measures.

Methodology: Inclusion criteria consisted of: 1) case-control study, cohort, cross-sectional, retrospective study and randomised controlled trials (RCTs); compared SMILE and FLEx for myopic correction; 2) any degree of myopia patients without history of ocular surgery and systemic disease; and 3) reported at least one of the outcome measures: logMAR corrected distance visual acuity (CDVA), logMAR uncorrected distance visual acuity (UDVA), loss of ≥2 lines of CDVA, UDVA20/20 or better, spherical equivalent (SE), SE within ±0.50 D, high-order aberrations (HOAs), central corneal thickness (CCT), corneal hysteresis (CH) and corneal resistance factor (CRF).

In the following databases, data source articles from January 2000 to 31 July 2015 were searched in PubMed, Medline, Embase and the Cochrane Library. Key words included the following terms: small incision lenticule extraction or femtosecond lenticule extraction and SMILE or FLEx. All of the selected comprehensive studies’ titles and abstracts were independently browsed by two authors (Wang JS and Jia Y). Then the two (Wang JS and Jia Y) carefully read the full texts of the remaining studies and their bibliographies to decide whether they met all of the inclusion criteria or not. No language restriction was used on the publications. Data was carefully collected into a standardised form from the included studies by two independent authors (Wang JS and Xie HT) according to the inclusion criteria. Quality assessment: Jadad scale was used to evaluate the methodologic quality of each study. The 95% confidence interval (CI), a pooled odds ratio (OR) with 95% CI and weighted mean difference (WMD) was calculated for summary estimates, dichotomous outcomes and continuous outcome, respectively. Meanwhile, statistical heterogeneity was assessed by the use of Chi-square test, tau² and Higgins I². If P<0.05, it was considered to be statistically significant.

Applicability/external validity: The authors acknowledged some limitations which need to be considered when interpreting the results. Firstly, the follow-up was finitude and disunion. Secondly, the limited number of included trials and small samples of each trial gave the analyses less power. Thirdly, only published data was included and publication bias may have existed. Last, but not least, the species of devices of femtosecond laser and instruments of eye examination were not considered in our research.

Geographic focus: No studies from Africa or from LMIC were included in this review.

Summary of quality assessment:

Medium confidence was attributed to this review’s findings. Although overall methods used were appropriate and rigorous, authors did not contact experts/authors for further studies as part of the search strategy. In addition, it is not clear if the search period was comprehensive enough that relevant literature was unlikely to be omitted.