Journal of Refractive Surgery

Original Article Supplemental Data

The Clinical Relationship of Anterior Capsular Tears and Vertical Spacing in the Femtosecond Laser Capsulotomy Procedure

Wendell J. Scott, MD; Shachar Tauber, MD; Craig D. Eck, MD; Rachel A. Scott, BA; Johann Ohly, MD

Abstract

PURPOSE:

To evaluate the frequency of anterior capsule tears and capsule edge irregularities in femtosecond laser anterior capsulotomy, including the effect of optimized vertical spacing settings.

METHODS:

Three thousand eight hundred thirty-four cases were examined and grouped according to the femtosecond laser capsulotomy settings using manufacturer default settings with a vertical spacing of 10, 15, and 20 µm. Capsulotomy edge irregularities and anterior capsule tears were recorded intraoperatively.

RESULTS:

The anterior capsule tear rates for the 10, 15, and 20 µm groups were 0.79%, 0.35%, and 0.09%, respectively. The capsule edge irregularity rates for the 10, 15, and 20 µm groups were 6.25%, 1.13%, and 1.15%, respectively. The treatment times for the 10, 15, and 20 µm groups were 1.6, 0.7, and 0.8 second, respectively. The risk reduction of anterior capsule tears positively correlated with the 15 and 20 µm group settings. The anterior capsule tear rate difference between the 10 and 20 µm group settings was statistically significant. Capsule edge irregularity rates were reduced in the 15 and 20 µm group settings. Eye movement was monitored in the 20 µm group and was observed in 9 of 13 patients with capsule edge irregularities.

CONCLUSIONS:

Anterior capsule tear rates are low with femtosecond laser cataract surgery. The rate can be further reduced with optimization of the settings, including an increase in vertical spacing.

[J Refract Surg. 2019;35(5):280–284.]

Abstract

PURPOSE:

To evaluate the frequency of anterior capsule tears and capsule edge irregularities in femtosecond laser anterior capsulotomy, including the effect of optimized vertical spacing settings.

METHODS:

Three thousand eight hundred thirty-four cases were examined and grouped according to the femtosecond laser capsulotomy settings using manufacturer default settings with a vertical spacing of 10, 15, and 20 µm. Capsulotomy edge irregularities and anterior capsule tears were recorded intraoperatively.

RESULTS:

The anterior capsule tear rates for the 10, 15, and 20 µm groups were 0.79%, 0.35%, and 0.09%, respectively. The capsule edge irregularity rates for the 10, 15, and 20 µm groups were 6.25%, 1.13%, and 1.15%, respectively. The treatment times for the 10, 15, and 20 µm groups were 1.6, 0.7, and 0.8 second, respectively. The risk reduction of anterior capsule tears positively correlated with the 15 and 20 µm group settings. The anterior capsule tear rate difference between the 10 and 20 µm group settings was statistically significant. Capsule edge irregularity rates were reduced in the 15 and 20 µm group settings. Eye movement was monitored in the 20 µm group and was observed in 9 of 13 patients with capsule edge irregularities.

CONCLUSIONS:

Anterior capsule tear rates are low with femtosecond laser cataract surgery. The rate can be further reduced with optimization of the settings, including an increase in vertical spacing.

[J Refract Surg. 2019;35(5):280–284.]

Laser cataract surgery is a relatively new method of cataract surgery that uses the femtosecond laser with intraoperative guided imaging.1 It has been reported to result in a more precise circular and reproducibly sized capsulotomy when compared to a manual capsulorrhexis.2 Laser capsulotomy was found to have a tensile strength superior to manual capsulorrhexis using a porcine model.3 Despite these findings, anterior capsule tears are a potential complication seen with both laser and manual methods (Table A, available in the online version of this article).4–35 Anterior capsule tears have been a common complication ever since the capsulotomy was attempted. The studies listed in the table were reviewed for their published anterior capsule tear rates in manual phacoemulsification and femtosecond laser–assisted cataract surgery. The studies looked at standard adult cataract cases unless noted. Pediatric cataract studies were excluded from this report. Studies were found using search tools on PubMed.gov. The reported incidence has been variable for each method. As a new and innovative method, particular attention has been focused on the laser capsulotomy.

Review of Anterior Capsule Tear Rates During Manual Phacoemulsification and FLACS4–35

Table A:

Review of Anterior Capsule Tear Rates During Manual Phacoemulsification and FLACS4–35

Two specific treatment details have been suggested as possible causes. One variable affecting the quality of the capsulotomy edge is the vertical profile of the femtosecond laser pulse and the vertical spacing between overlapping laser pulses. Stanford scientists have shown that the femtosecond laser pulse effect is vertically elongated.36 With this knowledge, we theorized that the vertical spacing was too close and that the overlapping spiral raster pattern was striking the capsule twice, creating capsule edge irregularities. We first reported the clinically observed rate of capsule edge irregularities with different vertical spacing settings.37

The importance of increased femtosecond laser vertical spacing settings was further supported by Schultz et al.28 They published pathology-supported scanning electron microscopy evidence that increasing the vertical spacing decreased capsule edge irregularities and also reported a low incidence of anterior capsule tear. A second variable is movement during laser treatment. Schultz et al.38 first noted eye movement as a possible contribution to anterior capsule tears. They demonstrated the importance of movement related to breathing during the capsulotomy treatment.

We report a large retrospective study of vertical spacing settings and the clinically observed relationship to capsule edge irregularities and anterior capsule tear, and propose the basis for the understanding of these phenomena.

Patients and Methods

A retrospective analysis of data from our quality assurance program was evaluated. The institutional review board determined that the study was compliant and could be submitted for publication. As part of this program, multiple elements of the femtosecond laser cataract surgery are reported by the surgeon and recorded by the laser technician and the circulating nurse during each surgery. Observation of the capsulotomy edge was made by the surgeon and reported to the circulating nurse after cortical removal, when details are most discernible. Retrospectively, the data were correlated with changes in the capsulotomy settings.

The data were classified into three groups with varied capsulotomy vertical spacing settings. The 10 µm group procedures were performed by three surgeons (WJS, ST, JO) using the manufacturer's default settings with a vertical spacing of 10 µm. The 15 and 20 µm group procedures were performed by one surgeon (WJS). The 10 µm group (1,551 cases) settings included: vertical spacing of 10 µm, horizontal spacing of 5 µm, power of 4 mJ, and incision depth of 600 µm and resulted in a treatment time of 1.95 seconds. The 15 µm group (1,155 cases) settings included: vertical spacing of 15 µm, horizontal spacing of 5 µm, power of 4 mJ, and incision depth of 400 µm and resulted in a treatment time of 0.7 second. The 20 µm group (1,128 cases) settings included: vertical spacing of 20 µm, horizontal spacing of 4 µm, power of 5 mJ, incision depth of 500 µm, and resulted in a treatment time of 0.8 second.

For the 20 µm group, cases were limited to on-label indications and all cases were digitally recorded. The central dimple-down procedure was used to assess whether or not the capsulotomy edge was free.39 In this procedure, viscoelastic is instilled into the anterior chamber and the cannula tip is used to depress the central capsulotomy disc. This downward indentation pulls the capsule edge centrally. This helps identify any micro-adhesions and applies forces that safely ensure the capsule is free. As part of the 20 µm group data only, correlations with patient movement were assessed if anterior capsule tear or capsule edge irregularities were present. In addition to intraoperative observation, HDV recordings were reviewed. A chi-square test of independence was performed to examine the relationship between vertical micron setting group and anterior capsule outcome (ie, whether or not there was an anterior capsule tear).

Results

The anterior capsule tear rates and the capsule edge irregularity rates for the three treatment setting groups were compared. The anterior capsule tear rates for the 10, 15, and 20 µm groups were 0.8%, 0.3%, and 0.1%, respectively (Figure 1). The capsule edge irregularities rates for the 10, 15, and 20 µm groups were 6.25%, 1.13%, and 1.15%, respectively (Figure 2). The risk reduction for anterior capsule tears positively correlated with the 15 and 20 µm group settings. The anterior capsule tear rate difference between the 10 and 20 µm group settings was statistically significant. Capsule edge irregularity rates were reduced for the 15 and 20 µm group settings. Eye movement was present in 9 of 13 patients with capsule edge irregularity in the 20 µm group. In the 20 µm group, 1,127 of 1,128 cases had no or minimal resistance to the dimple-down technique. Forceps were used in one case, but there were no uncut areas.

Anterior capsule tear rates for the different vertical spacing settings.

Figure 1.

Anterior capsule tear rates for the different vertical spacing settings.

Capsule edge irregularities rates for the different vertical spacing settings.

Figure 2.

Capsule edge irregularities rates for the different vertical spacing settings.

For the 20 µm group, there was one radial anterior capsule tear resulting in a rate of 0.1% (1 of 1,128). This tear did not extend posteriorly. It was located inferiorly at the 7-o'clock position. There were also capsule edge irregularities present at the 5-o'clock position inferiorly. Intraoperative and video analysis revealed inferior cornea surface epithelial clouding in this patient with known dry eye syndrome. One patient with an anterior capsule tear that was excluded because the femtosecond laser treatment was aborted due to patient movement.

The relationship between vertical micron setting group and anterior capsule tears was significant: X^2 (2, N = 3,798) = 7.517, P = .023. Patients in the 15 and 20 µm groups were less likely to have anterior capsule tears than patients in the 10 µm group. Specifically, 0.8% of patients in the 10 µm group, 0.3% of patients in the 15 µm group, and 0.1% of patients in the 20 µm group had anterior capsule tears. A chi-square test was the statistical test of choice because the 10, 15, and 20 µm groups were treated as categorical variables. The settings between the three groups included variance predominantly in the vertical setting, but also included changes to incision depth and power, making the categorical comparison most appropriate.

Discussion

The safety of any new technology is of paramount importance and the femtosecond laser capsulotomy has received attention due to concern about anterior capsule tears raised by a report from an early experience.13 Although this did not reflect the experience of others at the time, it did bring attention to the fact that anterior capsule tears can occur with the femtosecond laser capsulotomy and encouraged us to better understand and refine the new technology.40

The presence of capsule edge irregularities has been noted across all femtosecond laser platforms.41 Mastropasqua et al.42 first reported that irregularities correlated with increasing energy. The importance of lower energy and decreasing laser pathway disruptions was demonstrated in a study comparing a soft versus hard patient interface using the LenSx laser system (Alcon Laboratories, Inc., Fort Worth, TX).43 These examples serve to remind us of the evolving understanding of the femtosecond laser capsulotomy.

To understand how micro-movement could affect the laser capsulotomy, it is necessary to consider how the capsulotomy is created. With the Catalys laser (Johnson & Johnson Vision, Santa Ana, CA), contiguously spaced femtosecond laser pulses progress posterior to anterior, relative to the capsule, in a spiral raster pattern. If there is no movement, the pattern will perfectly overlap in the vertical plane. However, if there is any horizontal movement, because the spiral raster pattern progresses, the vertical overlapping pulses could be off-axis horizontally. That could cause the capsule to be weakened at the point(s), causing capsule edge irregularities and contributing to anterior capsule tear. However, this can only occur if the vertical effect of the laser pulse in the vertical plane overlaps and is too close, therefore striking the capsule twice and causing two full-thickness disruptions in the horizontal plane (Figure A, available in the online version of this article).

Figure demonstrating that ideally the capsulotomy laser bursts will line up vertically to create a single perforation in the anterior (left side). However, with small horizontal head movements during the capsulotomy sequence, the laser bursts will not line up vertically, leading to offset microperforations (right side) and creating areas of weakness that could become anterior capsule irregularities and tears.

Figure A.

Figure demonstrating that ideally the capsulotomy laser bursts will line up vertically to create a single perforation in the anterior (left side). However, with small horizontal head movements during the capsulotomy sequence, the laser bursts will not line up vertically, leading to offset microperforations (right side) and creating areas of weakness that could become anterior capsule irregularities and tears.

In the case of the femtosecond laser capsulotomy, early-adopting surgeons assumed that the settings for the capsulotomy were fully optimized. The settings were based on porcine capsules, which are significantly thicker than the human capsule, and required overlying laser pulses in a vertical raster pattern to cut the capsule. Settings were optimized for strength based on the 50 to 66 µm thickness of the porcine capsules.44 The human capsule is four to five times thinner, ranging from 11 to 16 µm.45 It can be cut with a single femtosecond laser pulse due to the vertically elongated effect. Thus, for the human capsulotomy using the Catalys femtosecond laser parameters, the optimal laser interaction is for a single pulse to cut the capsule as the spiral raster pattern progresses. Overlapping pulses are inefficient and not necessary. More important, an overlapping pulse that partially cuts the capsule at a point offline from the intended capsulotomy can lead to a radial point of capsule weakness and a potential radial anterior capsule tear. Increasing the vertical spacing decreases the risk of laser pulses striking the capsule in an unintended way. Also, horizontal displacement can occur with micro-eye movement. The longer it takes to perform the capsulotomy, the more likely this is to occur. Increasing the vertical spacing and decreasing the incision depth decreases the time needed to complete the capsulotomy and decreases the energy needed.

Our study found a low anterior capsule tear rate for the femtosecond laser capsulotomy. These findings are consistent with other reports of rates of 0.1% and 0.18% using different laser platforms.14,20 Collectively, these reports confirm the safety of the femtosecond laser capsulotomy.

Retrospective studies should always be viewed with caveats in mind. Consideration of operative technique and other factors that may have influenced the findings should be examined. The incision depth varied for each group. In cases of extreme vertical eye movement or vacuum loss, the laser pulse could miss the capsule and this could have affected the 15 µm group data (incision depth 400 µm). Also, at the time the 15 µm group data were collected, off-label cases may have been included in the treatment group. The 20 µm group data included on-label cases only and changes in the horizontal spacing, power setting, and vertical setting, which should be taken into consideration for surgeons adopting the 20 µm group settings. The 20 µm group used the greatest vertical setting that is currently approved. Because the effect of the Catalys femtosecond laser pulse is greater vertically, in theory, it is possible that the optimal vertical setting could be greater than 20 µm. To further test this theory, the setting range approved by the U.S. Food and Drug Administration would need to be expanded and revised. Finally, the identification of capsule edge irregularities on video review is not comparable to scanning laser microscopy examination as a primary or secondary outcome.

In our clinical experience, increasing the vertical spacing setting to 15 µm decreased capsule edge irregularities. Based on this experience, capsulotomy settings were further modified. The results are represented by the 20 µm group data and show fewer anterior capsule tears. However, there was not a statistically significant difference in the anterior capsule tear or capsule edge irregularity rates for the 15 and 20 µm group settings. Because the 15 µm group data included potentially more difficult off-label cases, the slightly higher anterior capsule tear rate may be explained by this difference. However, by using the 20 µm group settings for on-label cases only, a clearer evaluation of the rate of anterior capsule tear with the Catalys laser can be made when compared to the rates of other lasers and methodologies, including manual capsulorrhexis techniques. For Catalys laser users, it is our recommendation that the other settings be changed along with the vertical setting. Current recommendations are for on-label use (vertical spacing of 15 µm, horizontal spacing of 4 µm, power of 4 mJ, incision depth of 400 to 500 µm vs 20 µm, horizontal spacing of 4 µm, power of 5 mJ, and incision depth of 400 to 500 µm). We recommend that users of this system investigate the vertical effect of the laser pulse by increasing the vertical spacing, using the dimple-down technique to carefully observe the capsulotomy edge and trypan blue capsule staining to highlight the capsulotomy edge whenever the surgeon has any question about the integrity of the capsulotomy. We cannot speak to any variances that may exist between different laser platforms with respect to the vertical effect of the laser pulse, and more investigation is needed.

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Review of Anterior Capsule Tear Rates During Manual Phacoemulsification and FLACS4–35

Study AuthorYearManual PhacoemulsificationFLACSNotesaFS Laser Platform Studied


No. of TearsNo. of CasesRate of TearsNo. of TearsNo. of CasesRate of Tears
Ng et al.1998381,0003.80%
Marques et al.2006212,6460.79%
Unal et al.2006152965.07%Resident manual cases
Olali et al.2007203585.59%
Chang et al.200843511.43%Complex cataracts manual
Bali et al.201282004.00%Early FS laserLenSx
Conrad-Hengerer et al.20131731.37%0730.00%Catalys
Reddy et al.20131631.59%1561.79%Victus
Abell et al.201418220.12%158041.87%Catalys
Day et al.201411,0000.10%Catalys
Conrad-Hengerer et al.201404000.00%Catalys
Mayer et al.201412000.50%FS laser learningLenSx
Chang et al.201491705.29%Early FS laserLensar
Abell et al.201552,2280.22%341,8521.84%Catalys
Conrad-Hengerer et al.20150980.00%1981.02%Catalys
Roberts et al.201573,3550.21%LenSx
Puri et al.2015253616.93%Resident manual cases
Hengerer et al.20152414.88%Intumescent cataracts
Genç et al.2016248030.00%Intumescent cataracts
Day et al.201601580.00%Early FS laserCatalys
Taravella et al.20163348.82%FS laser in complex casesLenSx
Nikolashin et al.201691078.41%Manual in complex cases
Asena et al.201611330.75%FS laser in complex vs normalLenSx
Schultz et al.201701000.00%Catalys
Nejat et al.20170210.00%Early FS laserVictus
Pittner et al.201721591.26%0460.00%Resident manual vs FS laserLenSx
Berk et al.201808830.00%49550.42%LenSx
Roelofs et al.2018514,3011.19%
Chee et al.20190580.00%White cataractsVictus
Roberts et al.201932001.50%62003.00%LenSx
Zhu et al.201986612.12%0660.00%White cataractsLenSx, Catalys, Victus
Authors

From Mercy Health System, Mercy Foundation, Springfield, Missouri (WJS, ST, JO); Saint Louis University, Saint Louis, Missouri (CDE); and Baylor College of Medicine, Houston, Texas (RAS).

The authors have no financial or proprietary interest in the materials presented herein.

AUTHOR CONTRIBUTIONS

Study concept and design (WJS, ST, JO); data collection (WJS, ST); analysis and interpretation of data (WJS, ST, CDE, RAS); writing the manuscript (WJS, RAS); critical revision of the manuscript (ST, CDE, RAS, JO); statistical expertise (RAS); obtaining funding (WJS); supervision (ST)

Correspondence: Wendell J. Scott, MD, Mercy Clinic Eye Specialists, 1229 E. Seminole St., Springfield, MO 65804. E-mail: Wendell.scott@mercy.net

Received: November 13, 2018
Accepted: April 09, 2019

10.3928/1081597X-20190410-04

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