Cataracts remains a major cause of vision impairment and blindness globally, profoundly impacting patients’ quality of life [1][2]. Surgical techniques for cataract repair have increasingly improved, with conventional phacoemulsification surgery (CPS) emerging as the gold standard due to its minimally invasive nature and swift recovery times. Nonetheless, dense cataracts, marked by significant opacification, present unique surgical challenges that can elevate the risk of complications and extend the duration of surgery [3].

Femtosecond laser-assisted cataract surgery (FLACS) is a cutting-edge innovation that harnesses femtosecond lasers to perform critical steps in cataract surgery, including anterior capsulotomy, lens fragmentation, and corneal incisions [4][5]. This procedure has been shown to provide superior precision, enhanced safety, and possibly improved visual outcomes compared to CPS, with a potential benefit in cases involving dense cataracts [5][6].

Previous meta-analyses have compared FLACS and CPS in patients with cataracts, but not in those with dense cataracts specifically [7][8]. FLACS achieves better visual outcomes in the early postoperative period and long-term follow-up, accompanied by more accurate capsulotomy and more optimized effective lens position than CPS [8]. However, no difference in visual outcomes has been shown after 6 months of follow-up. Despite this, the comparative effectiveness of FLACS versus CPS for dense cataracts remains a subject of lively debate [9][10]. Numerous studies have explored this comparison and yielded inconsistent findings. While some indicate that FLACS may reduce the reliance on ultrasound energy and decrease surgical time, others show no significant differences in visual acuity or complication rates [6][10].

Given this controversy, we aimed to perform a systematic review and meta-analysis of surgical outcomes associated with FLACS versus CPS for patients with dense cataracts.

This systematic review and meta-analysis adhered to the guidelines outlined in the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) [11] and followed the recommendations of the Cochrane Handbook for Systematic Reviews of Interventions [12]. This study did not involve the handling or processing of individual patient data. The protocol was prospectively registered at the International Prospective Register for Systematic Reviews (PROSPERO) in August 2024, ID: CRD42024579055.

This meta-analysis compared the outcomes of FLACS and CPS for dense cataracts by pooling the data from 19 studies with a total of 5433 cases. Our findings indicate that FLACS significantly reduced EPT and CDE compared to CPS. However, there were no significant differences in ECD, percentage ECD loss, or CCT, regardless of time of follow-up.

Cataracts remains a major cause of vision impairment and blindness globally [1]. Importantly, dense cataracts challenge the surgeon due to the need for prolonged phacoemulsification time and increased ultrasound energy, often leading to endothelial cell damage and corneal edema [3]. Our findings indicate that the reduction in EPT and CDE associated with FLACS for patients with dense cataracts is noteworthy and clinically relevant. By pre-fragmenting the lens with femtosecond laser technology, FLACS minimizes the reliance on ultrasound energy, thereby reducing CDE. This reduction can potentially improve postoperative recovery by limiting collateral thermal damage to surrounding ocular tissues.

A previous meta-analysis compared both techniques in patients cataracts, although without a dedicated subgroup assessment of dense cataracts. Both FLACS and CPS were found to be effective and safe, although FLACS required less ultrasound energy, with a more precise treatment [30]. There was no significant difference in visual acuity between both methods at 6 months. Our results align with previous studies that reported advantages of FLACS over CPS for energy consumption and surgical efficiency, especially in complex cases [6]. For example, study by Hatch et al. [24] demonstrated similar reductions in EPT, supporting the hypothesis that FLACS may enhance surgical outcomes in cases of advanced lens opacification.

Despite the reduction in surgical energy, FLACS did not yield a significant benefit for ECD preservation or CCT reduction. These findings suggest that whilst FLACS reduces intraocular trauma associated with ultrasound energy, it may not directly impact endothelial cell loss in the short-term. The lack of significant ECD differences could be attributed to the cumulative effect of other surgical factors, including fluid turbulence and surgical manipulation during lens removal, which remain common to both FLACS and CPS.

The primary strength of this meta-analysis lies in its inclusion of 19 studies, which provides a robust pooled analysis of surgical outcomes in dense cataracts. By demonstrating significant reductions in EPT and CDE, our findings highlight the role of FLACS as a valuable tool in minimizing intraoperative energy use. This benefit is particularly relevant for patients with preexisting corneal compromise, where excessive energy usage may exacerbate endothelial cell loss [9]. Our findings support the use of FLACS as a preferable technique in cases of dense cataracts where minimizing phacoemulsification time and energy is critical. However, the decision to adopt FLACS must be balanced with cost considerations, equipment availability, and surgeon familiarity with the technology. Currently, in clinical practice, most surgeons use CPS due to the high cost of femtosecond laser equipment [31][32].

This study is not without limitations. First, there was significant heterogeneity in outcomes, which may reflect differences in study design, surgical techniques, and patient populations between studies. Nevertheless, we performed leave-one-out sensitivity analyses and confirmed that findings were not dependent on one given study for any outcome. Second, most of the included studies were observational, which are associated with a higher risk of bias, particularly confounding. Due to the absence of patient-level data, we could not perform and multivariate adjusted analysis to minimize confounding in observational studies. Third, the follow-up duration was inconsistent across studies, with some failing to assess long-term endothelial outcomes or visual acuity. Lastly, variations in FLACS platforms (e.g., LenSx, Catalys, Victus) and differences in the definition of “dense cataract” may have influenced the results. Standardized protocols for assessing cataract density and surgical outcomes are needed to improve comparability among studies.

Reducing CDE is very important for cases of cornea with low endothelial cell count, guttata, in elderly patients. In the papers included in this meta-analysis, the surgeon’s experience was not cited, contributing to the heterogeneity of the meta-analysis. Another limitation of this meta-analysis is the short follow-up time of patients for better assessment of corneal health. For future studies, it would be important to develop a single classification system for cataract staging to improve comparability between studies. Future studies could also investigate other variables such as posterior capsule rupture and posterior capsule opacity.

FLACS offers significant advantages over CPS in reducing ECT and CDE for dense cataracts. However, its impact on endothelial health remains inconclusive. While FLACS shows promise as a safer and more efficient surgical approach for dense cataracts, high-quality RCTs with standardized methodologies are warranted to validate our findings and explore the long-term impact of FLACS on visual outcomes, endothelial health, and patient satisfaction. Studies focusing on cost-effectiveness and learning curves associated with FLACS adoption will also be critical for broader clinical implementation.

All authors take responsibility for all aspects of the reliability and freedom from bias of the data presented and their discussed interpretation.

Table S1. Search strategy.

Figure S1. % ECD loss at one week and one month.

Figure S2. CCT at one day, one week, one month and three months.

EPT

ECD

CDE

CCT

Figure S3. Risk of bias summary for randomized studies.

Figure S4. Risk of bias summary for non-randomized studies.