FormalPara Key Summary Points

Why carry out this study?

Although rare, capsulotomy-related complications, including incomplete capsulotomy, anterior capsule tags and anterior capsule tears, have been reported to occur in femtosecond laser-assisted cataract surgery (FLACS).

Furthermore, there is currently no agreement on the optimal irradiation thickness of capsulotomy to minimize capsulotomy-related complications.

The present study aimed to examine the efficacy of a new, modified technique for determining capsulotomy irradiation thickness in reducing capsulotomy-related complications.

What was learned from the study?

Compared to the conventional technique, the modified capsulotomy technique significantly reduced the incidence of incomplete capsulotomy, anterior capsule tags and anterior capsule tears.

The modified technique for determining capsulotomy irradiation thickness can be adopted as a standard approach in FLACS to minimize capsulotomy-related problems.

Introduction

The introduction of femtosecond laser into cataract surgery in 2008 resulted in an increase in capsulotomy accuracy and a decline in conventional phacoemulsification reports [1, 2]. Therefore, it was thought that femtosecond laser technology improved the safety and accuracy of cataract surgery. The quality of anterior capsulotomy has been shown to influence the incidence of complications during cataract surgery, and it is considered one of the most challenging steps for novice and inexperienced surgeons [3]. In this regard, the combination of high-resolution anterior segment optical coherence tomography (OCT) and laser technology has improved the safety of cataract surgery by enhancing the reproducibility of capsulotomy with a reduced likelihood of anterior capsule tear. However, in a study by Abell et al., the incidence of anterior capsule tags was reported as 1.62% in the femtosecond laser-assisted cataract surgery (FLACS) group versus 0.004% in the manual procedure group, and the incidence of anterior capsule tears was 1.84% in the FLACS versus 0.22% in the manual procedure group, with the differences being statistically significant (P < 0.001) [4]. In addition, Kolb et al. reported in their systematic review and meta-analysis comparing FLACS with conventional cataract surgery that, while FLACS was beneficial for patients with low endothelial cell density and dense cataracts, and postoperative visual acuity at the medium-term follow-up was slightly better than for the manual procedure, incidences of capsular complications were higher in FLACS [5]. Furthermore, in a similar systematic review and meta-analysis, Wang et al. reported that FLACS did not improve the rates of either intra- or postoperative complications compared to the manual procedure [6].

In addition, past studies on FLACS have reported varying rates of incomplete capsulotomy, with a broad range of 0–12% [7,8,9]. Thus, the assessment of clinical advantages of FLACS was more complex than previously thought, particularly in terms of capsulotomy-related complications.

Although incomplete capsulotomy, anterior capsule tags and anterior capsule tears are relatively rare in FLACS, their occurrence can complicate cataract surgery. Therefore, there is a need to improve the technique of femtosecond laser-assisted capsulotomy to reduce the frequency of capsulotomy-related complications. Nonetheless, there is a lack of consensus on the optimal irradiation thickness of capsulotomy to minimize the incidence of capsulotomy-related complications.

The purpose of the present study was to investigate the efficacy of a unique, modified technique for determining the irradiation thickness of capsulotomy. To the best of our knowledge, this is the first study to examine this approach in FLACS using the LenSx platform.

Methods

Study Design and Patient Selection

This open-label, prospective, comparative cohort study was performed at a private eye clinic between January 2020 and December 2022. The Yokosuka Chuoh Eye Clinic Ethical Committee (reference no. 2022-004) approved the research protocol, and the data collection process adhered to the tenets of the Declaration of Helsinki of 1964. Written informed consent was obtained from all patients after providing a detailed explanation of the procedure and its possible outcomes.

A femtosecond laser platform (LenSx platform, Alcon Laboratories, Inc., Fort Worth, TX, USA) was used to compare the incidences of incomplete capsulotomy, anterior capsule tags and tears, and posterior capsule tears between the conventional and modified capsulotomy techniques.

This study included patients with binocular cataracts, no history of ocular trauma and surgery, no corneal scarring and dystrophy, no ocular disease other than cataracts, no signs of zonular weakness, and no docking failure or eye movement encountered during femtosecond laser treatment. Patients with pupil diameter < 6 mm after the usage of mydriatics, mature cataracts, and significant subcapsular opacity (calcification) were excluded from the study. Capsulotomy was created by using the modified technique in one eye (Group 1, 220 eyes) and the conventional technique in the other eye (Group 2, 220 eyes).

Preoperative Assessment

A comprehensive preoperative assessment was performed for all eyes. Nuclear hardness was graded by a single ophthalmologist using the Emery-Little classification system [10]. K-value and anterior chamber depth (ACD) were checked with anterior segment swept-source OCT device (CASIA 2, Tomey Corporation, Nagoya, Japan), and the axial length (AL) was determined using a swept-source OCT biometer (IOLMaster 700, Carl Zeiss, AG, Jena, Germany).

Laser Parameters and Settings

All FLACS procedures were performed using the femtosecond laser platform with the same default settings. A 5.3-mm capsulotomy centered on white-to-white was made with 8.0 mJ energy (spot and layer separations: 9 μm each). Nuclear fragmentation was done using the chop and cylinder technique with 8.0 mJ energy (spot and layer separations: 9 μm each).

Surgical Technique

A single surgeon performed all operations using the same procedure. There was a gap of 1–2 weeks between the operation dates of one eye and the other eye. The capsulotomy and lens fragmentation were performed using the femtosecond laser. Using anterior segment OCT imaging, different irradiation thicknesses were applied for capsulotomy in each eye of the same patient as follows: In Group 1, the irradiation thickness for the capsulotomy was set between the upper edge of the highest point of the anterior capsule and the lower edge of the lowest point of the anterior capsule (modified technique) (Fig. 1A). In Group 2, the irradiation thickness was set between the center of the highest point of the anterior capsule and the center of the lowest point of the anterior capsule (conventional technique) (Fig. 1B). In both groups, the anterior (delta up) and posterior (delta down) offsets were set at 300 µm and 350 µm, respectively (Fig. 2). A 2.2-mm corneal limbus incision and a 1.0-mm corneal side incision were created with a disposable stainless-steel surgical blade (Mani, Inc. Tochigi, Japan). The soft-shell technique was used to fill the anterior chamber with a dispersive viscoelastic Viscoat (Alcon Laboratories, Fort Worth, TX, USA) and a cohesive viscoelastic, Opelead (Senju Pharmaceutical Co., Ltd. Osaka, Japan) [11].

Fig. 1
figure 1

Zoomed-in cross-sectional images of anterior capsule in anterior segment optical coherence tomography in LenSx. A Group 1 (modified technique): irradiation thickness for capsulotomy was set between the upper edge of the highest point of the anterior capsule (yellow arrow) and the lower edge of the lowest point of the anterior capsule (red arrow). B Group 2 (conventional technique): irradiation thickness for capsulotomy was set between the center of the highest point of the anterior capsule (blue arrow) and the center of the lowest point of the anterior capsule (green arrow)

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Fig. 2
figure 2

Zoomed-out cross-sectional image of lens in anterior segment optical coherence tomography in LenSx. In both groups, anterior and posterior offsets (delta up and down offsets) for capsulotomy were set at 300 µm (yellow circle) and 350 µm (red circle), respectively. Total irradiation thickness was the sum of the set irradiation thickness (modified technique or conventional technique) and the anterior and posterior offsets

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The quality of capsulotomy was assessed by using the central dimple-down technique to confirm the completion of a continuous 360-degree cut of the anterior capsule with a free disk [12]. In addition, capsule forceps were used to thoroughly inspect the completion of capsulotomy and check for capsule tags and tears. Furthermore, the presence of tags and tears was double checked following aspiration of the lens cortex. Thereafter, cortico-cleaving hydrodissection was conducted following the removal of anterior capsulotomy with the rhexis forceps.

Phacoemulsification and aspiration were performed using the Centurion Vision System (Alcon Laboratories, Inc. Fort Worth, TX, USA). Following complete removal of the cataract, the surgeon conducted a thorough examination for capsule tags and tears. Subsequently, the capsule bag was infused with Opelead, and an intraocular lens (IOL), Clareon (Alcon Laboratories, Inc. Fort Worth, TX, USA), was placed into the capsule bag. The ophthalmic viscoelastic device was fully removed prior to checking for watertight sealing of the corneal incision.

Statistical Analyses

Statistical analyses were done to compare the relevant variables between Group 1 and Group 2. Baseline characteristics, including cataract grade, K-value, ACD and AL, were compared as preoperative variables, while irradiation thickness was compared as a procedural variable. The incidences of incomplete capsulotomy, anterior capsule tags and tears, and posterior capsule tears were also compared. Additionally, in both groups, the distance between the center of the highest point of the anterior capsule and the center of the lowest point of the anterior capsule was also investigated.

Normality of variable distribution was examined using the Shapiro-Wilk test. According to the results of the normality test, Wilcoxon signed-rank test or t-test was used to compare baseline characteristics and irradiation thickness. The same applied to the intergroup comparison of the distance between the center of the highest point of the anterior capsule and the center of the lowest part of the anterior capsule. Chi-square test was used for the comparison of incidences of incomplete capsulotomy, anterior capsule tags and tears, and posterior capsule tears.

All statistical analyses were done using the SPSS software (v. 25.0, IBM SPSS statistics, Armonk, NY, USA), and P < 0.05 was regarded as statistically significant. Post hoc analysis was performed using G*power (v. 3.1.9.7) to confirm whether the power of sample size was significant.

Results

This study assessed a total of 440 eyes, including 220 eyes in Group 1 (modified technique group) and 220 eyes in Group 2 (conventional technique group). Average age of the study population was 70.17 ± 7.00 years.

There were no significant differences in the baseline characteristics (cataract grade, K-value, ACD and AL) between the two groups (Table 1). Table 2 shows the differences in the mean irradiation thicknesses of Group 1 and Group 2; these differences were statistically significant (P < 0.001). However, the difference in the mean distance between the center of the highest point of the anterior capsule and the center of the lowest part of the anterior capsule between Group 1 and Group 2 was not statistically significant (P = 0.32) (Table 2). Therefore, it can be inferred that there was no significant difference in the docking angle at patient interface between Groups 1 and 2.

Table 1 Baseline characteristics
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Table 2 Laser irradiation thickness
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Table 3 shows the rates of incomplete capsulotomy and anterior capsule tags and tears in both groups. Compared with Group 1, Group 2 had significantly higher rates of incomplete capsulotomy as well as anterior capsule tags and tears (P = 0.006, 0.005, 0.015, respectively). Posterior capsule tears were not observed in either group.

Table 3 Incidences of incomplete capsulotomy and anterior capsule tags and tears
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The post hoc power analysis for a given sample size (n = 440) showed a statistical power (1 − β) of 1.000 with a significance level of 0.05.

Discussion

This study revealed that the modified capsulotomy technique significantly decreased the incidence of incomplete capsulotomy, anterior capsule tags and anterior capsule tears compared to the conventional technique. These findings may be able to compensate for one of the major drawbacks (capsulotomy-related complications) of FLACS [13].

Reduction in total phacoemulsification time and endothelial cell loss and improvement in the accuracy of arcuate keratotomy incisions are the principal benefits of FLACS [13]. Another substantial advantage of FLACS over manual surgery is the production of precise and reproducible capsulotomy size and shape [14,15,16,17,18]. Previous reports have indicated that more precisely sized, shaped and centered capsulotomies can significantly increase the possibility of complete coverage of the IOL edge with capsulorhexis while decreasing the incidences of posterior capsule opacification and anterior capsule contraction rate [19,20,21,22,23]. This advantage is especially vital for cataract surgeries with premium IOLs, such as aspheric, toric and multifocal IOLs [19,20,21,22,23].

The above-stated facts support the superiority of FLACS over the manual procedure. However, a previous study has reported a higher incidence of incomplete capsulotomy and anterior capsule tags and tears in FLACS compared with the manual procedure [4]. To overcome this disadvantage, a soft lens-assisted contact patient interface (LaserSoftFit, Alcon LenSx Lasers Inc., Fort Worth, TX, USA) was introduced for laser cataract surgery platforms. Although this led to a significant reduction in the rates of incomplete capsulotomy and anterior capsule tags and tears in FLACS, these complications still occur. The incidences vary from report to report. For instance, using the VICTUS femtosecond laser system (Bausch + Lomb Company, Munich, Germany), Panthier et al. reported incomplete capsulotomy in 23% and anterior capsule tags in 24.4% of patients who received FLACS in their study [18]. On the other hand, utilizing the LenSx platform, Michael et al. found anterior capsule tags and tears in 10.5% and 7.5% of patients, respectively [9]. In addition, Abell et al. reported incomplete capsulotomy, anterior capsule tags and anterior capsule tears in 1.13, 1.64 and 1.84% of cases, respectively, using the Catalys laser system (Optimedica, Santa Clara, CA, USA) [4].

Furthermore, it has been shown that the surgeon’s experience level has a significant impact on the rates of capsulotomy-related complications during FLACS. In a study by Roberts et al., the incidences of anterior capsule tags and tears were reported as 10.5% and 4% in the inexperienced doctor group and 1.61% and 0.31% in the experienced doctor group, respectively. In addition, these differences were found to be statistically significant (P < 0.001) [24]. Therefore, there is a demand for techniques that can produce consistent results regardless of a doctor’s experience level.

According to Wang et al., the most significant causes of incomplete capsulotomy included eye movement during operation (30.77%), presence of air bubbles or ocular secretions at the patient interface (26.92%) and white cataracts (13.46%). Additionally, 54.55% of anterior capsule tears were caused when the surgeon attempted to complete the capsulotomy manually following an incomplete femtosecond laser capsulotomy [25].

These results indicate that even if there is no problem with the quality of docking, capsulotomy-related complications can occur. In this regard, few previous studies have reported the effectiveness of modifying the default laser parameters in minimizing capsulotomy-related complications. Schultz et al. reported that increasing the vertical spot spacing from 10 to 15 µm led to a reduction in capsular complications associated with FLACS [26]. Scott et al. also demonstrated similar results in their study [27]. Additionally, Patzlaff et al. reported the advantage of smaller laser spot distances in enhancing the tear resistance of porcine lens capsules after femtosecond laser-assisted capsulotomy [28]. However, there is a lack of evidence in the existing literature regarding the usefulness of changing laser irradiation settings during operation in reducing FLACS associated capsular complications. This highlights the need for modified techniques to reduce these unwanted occurrences and achieve full benefit of capsulotomy with FLACS. This prompted us to develop a new, modified technique of determining the capsulotomy thickness in FLACS. As far as we know, this research is unique, and no other study has reported a similar technique.

Moreover, there is currently no agreement on the optimal irradiation thickness of capsulotomy to reduce capsulotomy-related problems. In the present study, the irradiation thickness of capsulotomy in the conventional technique group (Group 2) was set according to the manufacturer’s instructions for the LenSx platform (between the center of the highest point of the anterior capsule and the center of the lowest part of the anterior capsule) (Fig. 1B). The rates of incomplete capsulotomy and anterior capsule tags and tears using conventional technique were 7.7%, 8.6% and 3.2%, respectively. In contrast, the rates of incomplete capsulotomy, and anterior capsule tags and tears were 1.8%, 2.3% and 0%, respectively, in the modified technique group (Group 1), where the irradiation thickness was set between the upper edge of the highest point of the anterior capsule and the lower edge of the lowest point of the anterior capsule (Fig. 1A). Moreover, these differences were statistically significant. In addition, there were no significant differences between the conventional and modified techniques in terms of the distance between the center of the highest point of the anterior capsule and the center of the lowest part of the anterior capsule. This also implies that no significant differences in docking quality existed between the two groups. Therefore, it is reasonable to conclude that the modified technique significantly reduced the chances of incomplete capsulotomy and anterior capsule tags and tears.

Additionally, while the irradiation width can be adjusted with the conventional method (delta up and down system) (Fig. 2), the modified technique clearly outperforms the conventional technique in two ways. First, there is no specific guidepost in the delta up and down system for setting the capsulotomy irradiation width, which may be challenging for an inexperienced surgeon when identifying the highest and lowest irradiation points. Second, while the delta up and down system is applied to unmagnified images, the highest and lowest irradiation points in the modified technique are set in a magnified image, which allows the surgeon to identify the setting points with enhanced accuracy.

Given the lack of consensus on the specific irradiation thickness in laser capsulotomy, the fact that this parameter (unlike the default laser parameter settings) can be controlled during operation and the findings of the present study clearly highlighting the benefits of the modified technique, it would be reasonable to recommend adopting this technique as the standard irradiation technique in clinical practice to reduce the risk of capsulotomy-related problems in FLACS performed via the LenSx platform.

There were some limitations to this study. First, the spot spacing and energy level of irradiation used during FLACS vary between medical facilities, even if the same femtosecond laser equipment is used, which can impact the surgical outcomes of FLACS. Second, compared to previous studies, the sample size in the present study was relatively small. Therefore, future studies with larger sample sizes are needed to confirm the generalizability of our findings. Third, we used the LenSx platform in this study, which uses an applanating (contact) patient interface. Talamo et al. reported in their study that, when compared to femtosecond laser equipment with a non-applanating (non-contact) patient interface, the one with an applanating patient interface is more vulnerable to corneal folds and these corneal folds can also be one of the causes of capsular complications [29]. Thus, variations in patient interface can result in different FLACS outcomes. Finally, in our study, only one surgeon performed all the procedures, and the outcomes may have differed between surgeons with varying levels of expertise and experience. This is something that needs to be investigated further.

Conclusion

In conclusion, the modified technique for setting irradiation thickness of capsulotomy in FLACS can be used as a new principle to minimize the incidences of capsulotomy-related problems while maximizing the benefits of FLACS.