Comparison of low-energy FLACS and conventional cataract surgery: meta-analysis and systematic review

Author: Yeh CY, Fang HS, Ou YC, Cheng CK, Wu TE.

Geographical coverage: Australia, Singapore, Taiwan, and Europe

Sector: Cataract surgery

Sub-sector: Conventional and laser-assisted procedures

Equity focus: Not reported

Study population: patients aged 18 years or older scheduled for routine cataract surgery

Review type: Effectiveness review

Quantitative synthesis method: Meta-analysis

Qualitative synthesis method: Not applicable

Background:

Cataract is the leading cause of reversible vision loss globally, with cataract surgery being the most common eye surgery. Conventional phacoemulsification surgery (CPS) involves manual steps and, while effective, complication rates can vary based on the surgeon’s experience. In 2009, femtosecond laser technology was introduced to cataract surgery, leading to femtosecond laser-assisted cataract surgery (FLACS). FLACS aims to improve precision and safety by using lasers for corneal incisions, capsulotomy, and lens fragmentation. Studies have shown that FLACS reduces mean phacoemulsification energy and effective phacoemulsification time (EPT), although no significant differences in long-term visual outcomes or complication rates have been observed compared to CPS. FLACS has been linked to higher prostaglandin levels and an increased risk of posterior capsular tears. Conventional FLACS uses high-energy laser pulses, which can cause tissue stress. The Femto LDV Z8 system uses low-energy, high-frequency laser pulses to minimise mechanical tearing, potentially reducing tissue stress.

Objective:

To compare the effectiveness of conventional phacoemulsification surgery (CPS) and low-energy femtosecond laser-assisted cataract surgery (FLACS) in patients with cataract.

Main findings:

Overall, the authors found that low-energy femtosecond laser-assisted cataract surgery (FLACS) showed potential benefits over conventional phacoemulsification surgery (CPS) in reducing endothelial cell loss and effective phacoemulsification time (EPT), although no significant differences in visual acuity or complication rates were observed.

The authors included 11 studies in the meta-analysis: seven randomised controlled trials, three prospective non-randomised comparative cohort studies, and one retrospective comparative case-control study. These studies were conducted in Australia (n=2), Singapore (n=2), Taiwan (n=1), and Europe (n=6), involving a total of 671 eyes treated with FLACS and 960 eyes treated with CPS. The mean age of patients ranged from 65 to 79 years, with follow-up durations ranging from 1 day to 18 months.

The authors found no statistically significant differences in postoperative corrected distance visual acuity (CDVA) between FLACS and CPS at 1-month (WMD, 0.001; 95% CI, -0.007 to 0.008) or 3-month (WMD, -0.001 letters; 95% CI, -0.013 to 0.011) follow-ups. FLACS significantly reduced EPT compared to CPS (WMD, -0.573 seconds; 95% CI, -0.809 to -0.337) but required a longer surgical time (WMD, 2.8 minutes; 95% CI, 1.337 to 4.262). FLACS also resulted in significantly less endothelial cell loss at the 1-, 3-, and 6-month follow-ups. However, no significant differences were observed in central corneal thickness (CCT) or aqueous cytokine levels between the two groups.

The authors note the need for further research addressing the long-term outcomes and potential side effects of low-energy FLACS compared to high-energy FLACS and CPS. They also suggest that studies should focus on standardising methodologies and reporting complications to provide more comprehensive data for meta-analyses. Additionally, they note that further investigation into the cost-effectiveness and patient satisfaction associated with these surgical techniques would be beneficial.

Methodology:

The authors searched the Cochrane Library, EMBASE, MEDLINE, PubMed, and Web of Science on 13 January 2023 without language restrictions for published clinical studies comparing low-energy FLACS and CPS in patients aged 18 years or older scheduled for routine cataract surgery. Studies had to involve human participants with a minimum follow-up period of 1 month. Animal studies, ex vivo studies, paediatric studies, and unpublished data were excluded. Studies that had cases already reported in previous studies were also excluded to avoid duplication.

Two reviewers followed a predetermined format to record information from the retrieved studies. Extracted data included the first author, year of publication, outcome measures (e.g., CDVA, ECD loss, EPT, and surgical time), and details about the cataract surgery (CPS or low-energy FLACS). Visual acuity values were converted from decimal to the logMAR scale if needed. Two researchers independently evaluated the risk of bias in each trial using the Cochrane Collaboration’s risk of bias tool for randomised controlled trials. Each trial was categorised as having a high, low, or unclear risk of bias. For cohort and case-control studies, the Newcastle–Ottawa Scale was used, with a score greater than 6 indicating good quality. Discrepancies were resolved through discussion and consensus. Statistical analysis was performed using Comprehensive Meta-Analysis software. The weighted mean difference (WMD) and 95% confidence intervals (CI) were calculated to assess changes in outcomes between the FLACS and CPS groups. For outcomes reported as medians, the values were converted to means; similarly, standard errors, 95% CIs, P values, ranges, and interquartile ranges were converted to standard deviations (SDs). Heterogeneity was calculated using the I² statistic, with I² > 50% indicating significant heterogeneity. A random-effects model was used to examine methodological and clinical heterogeneity. Statistical significance was defined as P < .05.

Applicability/external validity:

The review discusses the generalisability of its findings, noting several limitations that could affect external validity. It includes a mix of study designs, with a significant proportion of observational studies, which may introduce biases. The review relied exclusively on published data, potentially leading to publication bias, since unpublished negative studies were excluded. The relatively small sample sizes and the recent introduction of the Femto LDV Z8 system also limit the generalisability of the results.

The review does not explicitly mention specific methods to assess applicability or external validity, but it does take steps to improve applicability by conducting a comprehensive literature review and performing subgroup analyses based on follow-up duration. It also acknowledges the need for larger, well-designed prospective trials with extended follow-up periods to validate and strengthen the findings. To improve applicability, the review suggests including unpublished studies and conducting more large-scale randomised controlled trials. These steps would help provide a more comprehensive analysis and enable better assessment of the long-term outcomes and potential side effects of low-energy FLACS compared to high-energy FLACS and CPS.

Geographic focus:

Included studies were conducted in Australia, Singapore, Taiwan, and Europe.

Summary quality assessment:

Overall, confidence in the conclusions of this review is low due to important methodological limitations. The search strategy was not sufficiently comprehensive to ensure that all relevant studies were identified. Additionally, the methods used to screen studies and extract data were not described in sufficient detail. The authors also did not analyse the data based on the risk of bias of the included studies.