An exploration of safe and efficient nucleus fragmentation strategies for femtosecond laser-assisted cataract surgery in short axial length patients

Abstract

Purepose

The intraoperative femtosecond laser time, Cumulative Dissipated Energy (CDE), Effective Phacoemulsification time (EPT), and intraoperative fluid perfusion volume were compared under different model fragmentation modes using Catalys femtosecond laser system.

Methods

This was a single-center, prospective, randomized controlled study. A total of 120 eyes who underwent femtosecond laser-assisted cataract phacoemulsification combined with intraocular lens implantation in Xiamen Eye Center affiliated to Xiamen University from September 2022 to March 2023 were randomly divided into 4 groups to undergo pre-nucleus splitting in different ways: Group 1: six-split, Group 2: eight-split, Group 3: six-split + gridded softening, and Group 4: eight-split + gridded softening. Patient age, gender, LOCS III grade, intraoperative femtosecond laser time, CDE, EPT, and intraoperative fluid perfusion volume were collected and analyzed.

Result

Result SNK test and Bonferroni test showed no significant difference in the nuclear hardness of lens, age, gender, AL, ACD, WTW and LT among the four groups (P > 0.05). Femtosecond laser time: Group 1: 44.87 ± 21.08s; Group 2: 43.10 ± 16.57s; Group 3: 50.70 ± 17.30s; Group 4: 64.04 ± 30.08s. There was no significantly different among groups 1, 2 and 3 (P > 0.05). However, the difference between group 4 and Group 1&2 was statistically significant (P_1.4= 0.006, P_2.4=0.00 2). There were no significant differences in CDE, EPT, and fluid perfusion between the four groups.

Conclusions

Short axial length patients may benefit more from the Catalys femtosecond laser system’s six or eight-split nucleus mode Settings, which produce the same or even more effective pre-split treatment than the mesh softening mode while using less femtosecond laser time.

Introduction

Cataract is one of the most common blinding eye illnesses in the world; the only effective approach to treat cataract is surgical removal of the cataract and implantation of an intraocular lens [1]. Cataracts remain the principal cause of blindness worldwide [2], accounting for nearly half of all cases of blindness in low-income countries and 5% in high-income countries [3, 4]. Over the past three decades, the global burden of vision impairment due to cataracts has significantly increased, with a 58.45% rise in prevalence and a 32.18% increase in Disability-Adjusted Life Years (DALY) rates [5]. Projections suggest that the global burden of cataracts will continue to escalate over the next 15 years [6].

With the rapid advancement of cataract and intraocular lens technologies, the prognosis of cataract surgery has shifted from basic visual recovery to improved visual quality and even quality of life [7]. In 2008, femtosecond laser-assisted cataract surgery (FLACS) was introduced as a novel procedure [8]. The femtosecond laser is used to automatically produce corneal incisions, capsulorhexis, lens fractures, and bow incisions after the Patient Interface (PI) is docked with the patient and the laser operation is designed [9]. A well-constructed corneal incision is crucial for cataract surgery, ensuring safety and minimal refractive impact. Additionally, the regularity and centration of the capsulorhexis significantly influence the position and diopter bias of the intraocular lens. The use of a femtosecond laser also alleviates our concerns in this regard [10].

Thanks to the establishment of FLACS on the foundation of femtosecond laser technology, it achieves an extremely minimally invasive and low-damage effect. This advantage not only enhances precision in surgeries for patients with normal ocular anatomy but also creates more favorable conditions for operating in narrow anterior segments [11, 12]. Individuals of Asian descent often have smaller anterior segments [13]. Patients with short axial lengths had shallow anterior chamber depths, and their corneas were nearer to the cataracts than those with normal-sized eyeballs. The release of phacoemulsification energy during the procedure can be considerably decreased by pre-treating the cataract nucleus with a femtosecond laser to break and soften it [14]. So FLACS can significantly reduce corneal endothelial cell loss during the operation [15, 16].

Building on this foundation, we aim to further explore the comparative effects of different nucleus fragmentation modes in patients with short axial lengths to identify the most suitable fragmentation mode for this population. Instead of flattening the cornea as is typically done [17], the Catalys femtosecond laser system (Abbott Medical Optics, USA) performs negative pressure suction through the marginal tissue of the corneaoscleral alone. However, Catalys Precision Laser System has only been operating in China for a little over two years and does not have a lot of clinical data from Asia. This study evaluated the efficacy and safety of femtosecond laser-assisted cataract surgery in short axial length patients, comparing different nucleus fragmentation modes. As the initial group of Chinese hospitals to use this technology.

Methods

Clinical data

This was a single-center, prospective, randomized controlled study. Received ethical approval from the Ethics Committee [XMYKZX-KY-2023-029] of our hospital for the safety of Catalys femtosecond laser system. After obtaining the patient’s informed consent at the same time, all surgeries were performed at Xiamen Eye Center, affiliated to Xiamen University, from September 2022 to March 2023. 120 patients with short axial length of the eye were randomized at random into 4 groups for various presplitting techniques: Six-split, eight-split, six-split plus gridded softening, and eight-split plus gridded softening make up Groups 1, 2, 3, and 4. The selection of different modes in a femtosecond laser system is shown in Fig. 1. The other settings, such as the capsular membrane tearing diameter (5.2 mm), the times of recurrent nucleus splitting (4 times), and the grid spacing (Frag: 500 m), remained constant. All patients received detailed preoperative evaluation. After sufficient mydriasis before surgery, the surgeon observed the degree of Lens turbidity and scored it according to Lens Opacities Classification System III (LOCS III): The conditions of lens cortex (C), nuclear opacity (NO), nuclear color (NC) and posterior subcapsular opacity (P) were observed. NC and NO were scored on a scale of 0.1 to 6.9. Additionally, patient information such as age, gender, axial length, anterior chamber depth, and lens thickness will be collected in detail.

Fig. 1.

The Catalys femtosecond laser system gives surgeons a variety of ways to perform nucleus fragmentation

The inclusion criteria for the cases are as follows: patients with cataracts who voluntarily accept FLACS surgery and have axial lengths between 20 mm and 23 mm, or glaucoma patients currently hospitalized for cataract surgery only.The exclusion criteria are as follows: (1) There is no history of previous ocular surgeries or trauma. (2) Normal pupil size, capable of dilating to 7 mm or greater. (3) No concurrent ocular conditions, apart from glaucoma, that may affect surgical procedures, such as conjunctivitis, keratitis, corneal opacities, or lens dislocation. (4) Exclusion of patients who have received astigmatism-correcting or multifocal intraocular lenses. (5) Exclusion of patients who experienced complications during the procedure. In this study, all patients participated as one individual with one eye undergoing surgery.

Considering that this study aims to explore the outcomes of FLACS (Femtolaser-Assisted Cataract Surgery) in patients with short axial lengths and recognizing that angle-closure glaucoma often presents with shorter axial lengths, we included a subset of glaucoma patients who underwent only cataract surgery. This decision was made to increase the number of eligible patients meeting the specified axial length criteria within a shorter timeframe.

Based on the patient sources within our department, we initially confirmed the inclusion of 40 glaucoma patients within 120 participants. We then assigned sequential numbers to the 40 glaucoma patients and the remaining 80 cataract patients separately. Following this, we utilized random grouping software to assign participants to groups, ensuring that the number of glaucoma patients was consistent across each group.

Operating procedure

The Catalys femtosecond laser system, the Centurion Vision System (Alcon Laboratories, Inc., USA), and the folding intraocular lens GCB00 (Abbott Medical Optics, USA) were implanted, and all patients were operated on by the same doctor.

Patients’ mydriasis (diameter > 7 mm), surface anesthesia, opening the eyelids in the supine position, femtosecond laser steps: PI negative pressure to attract fixed eyeballs, Catalys system through its Integral Guidance (IG) integrated guidance technology to conduct a full range of three-dimensional high-definition OCT imaging of the anterior segment, and generate the anterior segment images of two sections, and set the laser parameters on this basis. Patients in different groups underwent varying styles of lens fragmentation, while all other settings remained consistent. The unitive parameters for femtosecond laser applications in capsulorhexis and lens fragmentation: For capsulorhexis, an incision depth of 600 μm, with horizontal spot spacing of 5 μm, vertical spot spacing of 10 μm, and pulse energy of 4.0 µJ, with a diameter of 5.2 mm. For lens fragmentation, the parameters consist of a seg-soft spacing of 600 μm, grid spacing of 500 μm, five segmentation repetitions, horizontal spot spacing of 10 μm, vertical spot spacing of 40 μm, anterior pulse energy of 8 µJ, posterior pulse energy of 10 µJ, and safety margins of 500 μm for both the anterior and posterior capsules. Follow-up work on the Catalys work platform continued, the bed was rotated, routine disinfection was performed, the main and lateral corneal incisions were separated by a blunt incision separator, and the anterior capsule was removed and its integrity was confirmed. The Centurion phacoemulsification handle sucked out the nucleus, the I/A sucked out the cortex, the anterior and posterior capsules were polished, and a foldable intraocular Lens GCB00 was implanted, watertight incision finally. All the procedures were successful, with no major problems such as posterior capsule rupture, detachment of the posterior elastic layer of the cornea, or secondary glaucoma. The following parameters were measured: femtosecond laser time, CDE, Effective Phacoemulsification time (EPT), and fluid perfusion. It is important to emphasize that the term “liquid perfusion” in this study refers solely to the volume of fluid consumed during the phacoemulsification removal of the nucleus and the irrigation/aspiration steps. We believe that it is meaningless to discuss the fluid consumption during the removal of the nucleus phase only.

Statistical method

For calculations, the SPSS 19.0 software was utilized. The study’s data were entered into the software and finally expressed as mean standard deviation (‾x ± s). The SNK and Bonferroni tests were used to determine whether the differences in variables between the four groups were significant. All parameters had a significance level of P ≤ 0.05.

Results

An overview of the basic characteristics of the patients participating in the project, detailing age, gender, operated eye, axial length, anterior chamber depth, white-to-white measurement, lens thickness, nuclear opalescence, and nuclear color, as shown in Table 1.

Table 1.

Basic information of four groups of patients

Information Group	Group1 (30)	Group2 (30)	Group3 (30)	Group4 (30)	P
Patient Characteristics
Age, Years, mean ± SD	61.23 ± 11.90	61.27 ± 10.01	66.43 ± 10.75	63.93 ± 9.30	0.229
Gender, Male, n(%)	8 (26.67%)	11 (36.67%)	8 (26.67%)	8 (26.67%)	0.780
Eye,Right,n(%)	13 (43.33%)	9 (30%)	10 (33.33%)	14 (46.67%)	0.494
Number of Glaucoma patients, n(%)	10 (33.33%)	10 (33.33%)	10 (33.33%)	10 (33.33%)	1
Ophthalmic Features
AL, mm, mean ± SD	21.54 ± 0.91	21.94 ± 0.96	21.40 ± 1.07	21.54 ± 0.92	0.158
ACD, mm, mean ± SD	2.32 ± 0.30	2.37 ± 0.29	2.24 ± 0.35	2.34 ± 0.32	0.392
LT, mm, mean ± SD	4.77 ± 0.35	4.76 ± 0.36	4.90 ± 0.32	4.91 ± 0.35	0.194
WTW, mm, mean ± SD	11.00 ± 0.35	11.07 ± 0.45	10.89 ± 0.42	10.95 ± 0.45	0.412
IOP, mmHg, mean ± SD	16.15 ± 3.66	15.43 ± 4.33	15.63 ± 4.00	15.01 ± 4.68	0.765
LOCS III Cataract Ratings
NO, mean ± SD	2.37 ± 1.07	2.63 ± 1.00	2.80 ± 0.89	2.83 ± 0.75	0.218
NC, mean ± SD	2.43 ± 1.04	2.67 ± 0.99	2.80 ± 0.76	2.83 ± 0.91	0.392

AL-Axial Length, ACD-Anterior Chamber Depth, LT-Lens Thickness, WTW-White To White, IOP-Intraocular Pressure, NO-Nuclear Opalescence, NC-Nuclear Color

The differences in femtosecond laser time, CDE, EPT, and fluid perfusion volume among the four groups, are shown in Table 2. Femtosecond laser time was as follows: Group 1 44.87 ± 21.08s; Group 2 43.10 ± 16.57s; Group 3 50.70 ± 17.30s; Group 4 64.04 ± 30.08s. It is evident that, aside from femtosecond laser time, there were no statistically significant differences in the other three observed indexes. Therefore, a further comparison of the femtosecond laser times among the four groups was conducted to observe the pairwise comparisons of these times. Table 3 displays the results of Bonferroni test. There was no statistically significant difference in femtosecond laser time between groups 1, 2, and 3 (P > 0.05), however, the difference between group 4 and groups 1 and 2 was (P_1.4=0.00 6, P_2.4=0.00 2). We further presented this data in the form of a bar chart, as illustrated in Fig. 2. It should be noted that the difference between Group 3 and Group 1 and Group 2 was not statistically significant; similarly, the difference between Group 3 and Group 4 was not statistically significant, but the average femtosecond time of Group 3 measured indicated that it was between the two. CDE, EPT, and fluid perfusion volume did not differ significantly amongst the four groups.

Table 2.

Comparison of femtosecond laser time, CDE, EPT and fluid perfusion volume among the four groups(mean ± SD)

Index Groups	Fstime	CDE	EPT	LPV
1	44.87 ± 21.08	3.71 ± 3.85	25.39 ± 22.09	48.47 ± 12.76
2	43.10 ± 16.57	4.22 ± 3.24	33.04 ± 24.39	56.13 ± 14.38
3	50.7 ± 17.30	6.65 ± 8.45	40.40 ± 41.45	53.67 ± 19.85
4	64.04 ± 30.08	6.27 ± 5.82	40.95 ± 28.71	53.67 ± 11.72
P	0.01	0.122	0.156	0.25

FStime-Femtosecond laser time, CDE-Cumulative Dissipated Energy, EPT-Effective Phacoemulsification time, LPV-Liquid perfusion volume

Table 3.

Multiple Comparisons of femtosecond laser times in each group

Dependent Variable: FStime
	(I) Group	(J) Group	Mean Deference	Std, Error	Sig.	95% Confidence interval
						Lower bound	Upper bound
Bonferroni	1	2	1.76667	5.66112	1	-13.4292	16.9626
		3	-5.83333	5.66112	1	-21.0292	9.3626
		4	-19.17333*	5.66112	0.006	-34.3692	-3.9774
	2	1	-1.76667	5.66112	1	-16.9626	13.4292
		3	-7.6	5.66112	1	-22.7959	7.5959
		4	-20.94000*	5.66112	0.002	-36.1359	-5.7441
	3	1	5.83333	5.66112	1	-9.3626	21.0292
		2	7.6	5.66112	1	-7.5959	22.7959
		4	-13.34	5.66112	0.121	-28.5359	1.8559
	4	1	19.17333*	5.66112	0.006	3.9774	34.3692
		2	20.94000*	5.66112	0.002	5.7441	36.1359
		3	13.34	5.66112	0.121	-1.8559	28.5359

* The mean difference is significant at the 0.05 level

Fig. 2.

The femtosecond laser time of Group1 and Group2 was significantly lower than that of Group4, and the difference was statistically significant

Discussion

In 2001, femtosecond lasers were utilized for the first time in refractive surgery to create corneal flaps. The device employs ultra-short laser pulses to split tissue at a predetermined depth, resulting in photoinduced rupture and the formation of a micro-cavitation bubble, which expands to form an excision plane, and the entire procedure is safe and exact [18]. To enhance the accuracy and safety of cataract surgery, Nagy et al. applied this technology for key phases such as corneal incision preparation, capsular tearing, and nucleus fragmentation [19].

Among various femtosecond laser systems, some researchers have found that non-contact devices, such as the Catalys system, establish a better and gentler contact with the patient’s eyes [20]. There are no corneal folds as there is no flattening contact mode. Instead of a negative pressure suction ring, the negative pressure required during surgery does not exceed 15mmHg, and the laser probe contact patients by liquid which are more comfortable [21]. Therefore, our hospital also introduced the Catalys femtosecond laser system when it was first introduced to China. We conducted this study at our institution due to the lack of clinical data on Asian patients with short axial lengths.

In this study, the Catalys femtosecond laser system was used to investigate the comparison of femtosecond laser time in different pre-nucleus splitting modes and the effect of different modes on CDE, EPT, and fluid perfusion volume in cataract phacoemulsification. 120 patients with short axial length of the eye were randomized into 4 groups for various presplitting techniques: Six-split, eight-split, six-split plus gridded softening, and eight-split plus gridded softening make up Groups 1, 2, 3, and 4. Ultimately, our results indicated that there were no statistically significant differences in CDE, EPT, and liquid perfusion among the four groups, even though we observed that the means for groups 3 and 4 were higher in these three aspects. However, it is noteworthy that in terms of femtosecond laser time, groups 1 and 2 were significantly lower than group 4, with group 3 falling in between. As early as 2012, Conrad-Hengerer et al. used the Catalys femtosecond laser system to perform pre-nucleus splitting using a mesh-like nucleus fragmentation mode at 350 μm separation parameters, and the results indicated that EPT and CDE were significantly reduced compared to 500 μm separation parameters [22]. Huseynova et al. found that the use of a denser pattern of nucleus fragmentation was effective in reducing CDE and EPT in cataract phacoemulsification [23]. However, we found that the addition of nucleus fragmentation treatment significantly increased the femtosecond laser time, but did not result in significant improvements in CDE, EPT, or fluid perfusion volume. Even in groups 3 and 4, the means for CDE, EPT, and fluid perfusion volume were higher, although these differences were not statistically significant. Our results are completely contrary to the conclusions of Conrad-Hengerer and Huseynova, especially because Conrad-Hengerer used a femtosecond instrument that was also Catalys, helps us to find out the reason.

We are currently considering the following factors: This is primarily based on the surgeon’s feedback, who stated that when the cataract nucleus is treated with six-split plus gridded softening or eight-split plus gridded softening, the advantage of divide-and-conquer surgery can be used to complete the cataract nucleus in an orderly and effective manner, as shown in Fig. 3, which is beneficial to improve the efficiency of the operation. The advantage of divide-and-conquer is greatly diminished when the cataract nucleus is treated with six-split plus gridded softening or eight-split plus gridded softening because the nucleus is too fragmented, the nucleus follows poorly during the phacoemulsification process, the processing time of the nucleus is prolonged, and even the release of the phacoemulsification energy is increased, as shown in Fig. 4. There is an increase in liquid perfusion naturally. Additionally, patients with short axial length often undergo cataract surgery earlier due to an inability to tolerate farsightedness [24, 25], leading us to find that this group is generally younger than typical cataract patients. Upon reviewing the data, we discovered that the median age of these 120 patients was 63 years, with the lower quartile dropping to as low as 55 years. Furthermore, we were surprised to find that the upper quartile for both NO and NC was only grade 3, indicating that this group of patients is generally younger and has softer cataract nuclei compared to typical cataract patients in China [26]. In other words, we believe that the softer nucleus could be one of the reasons for our differing conclusions compared to previous scholars. Softer cataract nuclei tend to have better integrity, making them easier to follow closely with the phacoemulsification needle during surgery. When the nucleus becomes overly fragmented, it may increase the workload of the procedure. As the surgeon noted, she did not perceive the surgical convenience typically associated with nucleus softening from the femtosecond laser; instead, she felt it increased unnecessary workload in most of these operations. Therefore, we suggest that when we need to soften the nucleus using a femtosecond laser, the phacoemulsification machine may also need to be modified. For example, we might need to increase the liquid flow rate properly or increase the negative pressure appropriately to guarantee the followability of small pieces. Finally, the study’s “segmentation softening spacing” value is 600 μm. Variations in these factors would likewise have an impact on the result which is different from other researchers. When the nucleus is divided into inappropriate sizes, it may neither reduce the burden of phaco energy nor maintain the overall consistency of the nucleus, resulting in poorer followability of the pieces. The 350 μm parameter, which is not set in this study, is not compared with our mesh-like spacing, which is likewise 500 μm. To make the conclusions more compelling, perhaps we can set up a contrast for these. However, the exact parameters that are appropriate for this process may require further exploration.

Fig. 3.

This is a cataract nucleus after eight-split processing. When the cataract is aspirated in the direction of the double-line arrow during surgery, the nearby nucleus can be further aspirated by moving in the direction of the single-line arrow

Fig. 4.

This is a cataract nucleus after softening treatment. Due to the weakened connections between the pieces of the cataract nucleus following softening, when one piece is aspirated, it does not effectively pull out the nearby pieces, resulting in poor continuity during the procedure

In light of these results, we may recommend that surgeons who are accustomed to using the divide-and-conquer method for cataract surgery consider employing the six-split or eight-split mode for FLACS when dealing with patients with less hard nuclei. Even without discussing whether these methods lead to lower CDE and EPT, simpler nucleus fragmentation can at least result in reduced femtosecond laser time.

It is noteworthy that we observed a slight increase in density from group 1 to group 4. However, it is important to emphasize that our study was conducted using a randomized grouping method, and there were no statistically significant differences in baseline data among the four groups. This indicates that, from a statistical standpoint, the four groups are comparable. Therefore, any differences in the outcomes among the four groups can be attributed solely to our intervention methods, that is the different nucleus fragmentations. Consequently, we believe that the primary reason for these results is the variation in different nucleus fragmentations. A significant limitation of this study is the absence of a traditional phacoemulsification group for comparison, as we did not anticipate such a research outcome in advance. In the meantime, the relatively small sample size may raise concerns regarding the testing power of the findings, which represents one of the limitations of this study. Finally, based on feedback from the surgeon involved in this experiment, it is important to note that, due to limitations in the study, only one surgeon was assigned to the procedures. This may significantly impact the results of the experiment.

To summarize, short axial length patients may benefit more from the Catalys femtosecond laser system’s six or eight-split nucleus mode Settings, which produce the same or even more effective pre-split treatment than the mesh softening mode while using less femtosecond laser time, but this conclusion is limited to the case of parameter settings in this study. Finally, given the small sample size of this study, more doctors or scholars are needed to participate in this study in the future to acquire more instructional results.

Author contributions

BL, LLC, and DKL collaboratively developed the research topic based on clinical needs and after reviewing the literature. BL and LLC conducted preoperative examinations on patients, and under the guidance of DKL, formulated the surgical plans. All surgeries were performed by DKL, with BL and LLC serving as surgical assistants. BL and LLC were responsible for the collection, statistical analysis, and calculation of the data. The manuscript was written under the guidance of DKL, based on the results of these analyses.

Funding

This study was supported by the Xiamen Municipal Bureau of Science and Technology (3502Z20244ZD1192) and the Fujian Provincial Natural Science Foundation of China (2024J011323).

Data availability

No datasets were generated or analysed during the current study.

Declarations

Ethics approval and consent to participate

This study has obtained ethical approval from the Ethics Committee [XMYKZX-KY-2023-029] of Xiamen Eye Center affiliated to Xiamen University to ensure the safety of the Catalys femtosecond laser system. All surgeries were performed at our institution after obtaining informed consent from the patients.

Consent for publication

All authors agree to publish their findings in this journal.

Competing interests

The authors declare no competing interests.