Methodological quality of the review: Medium confidence

Author: Kolb CM, Shajari M, Mathys L, Herrmann E, Petermann K, Mayer WJ, Priglinger S, Kohnen T.

Region: Australia, Europe, America and Asia

Sector: Biomedical

Subsector: Treatment

Equity focus: Not stated

Review type: Other review

Quantitative synthesis method: Meta-analysis

Qualitative synthesis method: Not applicable

Background:
Because cataract is the most common cause for blindness, cataract surgery is the most frequently performed ophthalmic operation. Conventional cataract surgery (CCS) is one of the safest surgical procedures in ophthalmology, but some intraoperative steps can be difficult, such as corneal incision, anterior capsulotomy and lens fragmentation. Ten years ago, Nagy et al. introduced the femtosecond laser that has since been used to assist in these critical steps during cataract surgery.

Objectives:
To compare the efficacy and safety of femtosecond laser-assisted cataract surgery (FLACS) with CCS.

Main findings:
In total, 73 studies (25 randomised controlled, 48 observational) were reviewed, with 12,769 eyes treated with FLACS and 12,274 eyes treated with CCS. In eyes treated with FLACS, uncorrected and corrected distance visual acuities and spherical equivalent after 1 month to 3 months (P=.04, P=.005, and P=.007, respectively) were better; total and effective phacoemulsification times were shorter (P<.001 each); cumulative dissipated energy was less (P<.001); circularity was more accurate (P<.001); central corneal thickness after 1 day and 1 month to 3 months was less (P<.001 and P=.004, respectively); and endothelial cell loss after 3 to 6 weeks and 3 months was less (P=.002 and P<.001, respectively) compared with CCS. Anterior capsule ruptures occurred more often with FLACS. No significant differences among groups were found in visual acuity at 1 week and after 6 months or in posterior capsule rupture rates and endothelial cell loss after 6 months.

For geographical location, 11 trials were conducted in Australia, 37 in Europe, 7 in America and 17 in Asia.

Based on these findings, authors concluded that both FLACS and CCS are effective and safe, although FLACS requires less energy and is a more precise treatment. However, mid-term visual acuity did not show any difference between the two methods.

Methodology:
To identify studies for inclusion, authors searched PubMed, Cochrane Library and Embase. Complete and published clinical prospective and retrospective trials whose primary aim was to compare FLACS and CCS were selected. Case reports, letters, reviews, editorials and pediatric trials were not considered. Only publications in English were included. The reference sections of retrieved original articles and reviews were scanned for studies that might have been missed in the primary searches. Research and data extraction were performed independently by two authors from 8 December, 2017, to 30 January, 2019.

The following visual and refractive outcomes were documented at different time points: uncorrected distance visual acuity (UDVA; 1 week, 1 month to 3 months, and 6 months or more); corrected distance visual acuity (CDVA; 1 week, 1 month to 3 months, and 6 months or more); spherical equivalent (SE; 1 week, 3 weeks to 3 months, and 6 months or more); mean absolute refractive prediction error (MAE; 1 week, 1 month to 3 months, and 6 months or more); and surgically induced astigmatism (SIA). To assess the quality of included RCTs, authors used the Cochrane Collaboration’s tool for risk of bias.

Authors conducted a meta-analysis by computing weighted mean differences (WMDs) with 95% CIs for continuous data types and odd ratio (ODs) with 95% CI for dichotomous outcomes. Statistical methods used were inversed variance for continuous data and Mantel-Haenszel for dichotomous data. Heterogeneity among the studies was determined using the x2 test and computing the I² statistic, with I² measures more than 50% being attributed to strong heterogeneity. When heterogeneity was indicated, random effects models were used, in other cases, fixed effect models were applied. Subgroup analyses of RCTs were performed. Funnel plots were analysed for evaluation of publication bias and small study effects. One-study-removal analysis was conducted to evaluate the sensitivity, or rather the change, if a single study was left out.

Applicability/external validity:
The authors report that although their findings can facilitate the choice of a certain procedure, limitations of included studies need to be considered for external use of the findings, including: heterogeneity among the studies –  comparing studies in which different lasers were used is not a balanced comparison.

Geographic focus:
Authors do not discuss applicability of findings to low and middle income countries.

Summary of quality assessment:
Overall, medium confidence was attributed to the conclusions about the effects of the intervention studied. Although authors used appropriate methods to pool data of included studies, literature searches were not comprehensive enough to ensure that all relevant studies were retrieved and therefore included in the review.