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Thermal capsulotomy: Initial clinical experience, intraoperative performance, safety, and early postoperative outcomes of precision pulse capsulotomy technology

Hooshmand, Joobin MBBS*; Abell, Robin G. MBBS; Allen, Penny PhD; Vote, Brendan J. MBBS

Author Information
Journal of Cataract & Refractive Surgery: March 2018 - Volume 44 - Issue 3 - p 355-361
doi: 10.1016/j.jcrs.2017.12.027
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Abstract

An anterior capsulotomy is an integral component of modern cataract surgery. A strong, appropriately sized, and well-centered capsulotomy facilitates safe manipulation during hydrodissection, nuclear removal, and insertion of the intraocular lens (IOL) and can ultimately define the success of cataract surgery.1–3 The anterior capsulotomy is typically performed using a continuous curvilinear capsulorhexis (CCC) and as phacoemulsification cataract surgery has evolved, the CCC has proven one of its most critical steps.3–6 New technologies attempt to improve the precision, safety, ease, and reproducibility of the anterior capsulotomy. One recent innovation is thermal capsulotomy performed using a precision pulse capsulotomy (PPC) device, marketed as Zepto (Mynosys Cellular Devices, Inc.).7

The PPC device consists of a disposable handpiece with an elastic circular nitinol cutting element at its tip, encased in a soft silicone suction cup. The tip is inserted into the anterior chamber through a 2.2 mm corneal incision. Once inside, the silicone cup is placed centrally and suction is applied to oppose the capsulotomy ring to the capsule. Brief pulses of electrical energy are then discharged through the nitinol ring to create the capsulotomy, after which the suction cup is released. The disposable handpiece is connected to an external control console operated by an assistant for the purpose of applying suction, energy, and release.

Preclinical testing in cadaver and rabbit eyes has shown smooth capsulotomy edges, minimal zonular fiber stress, negligible anterior chamber temperature changes, and no difference in corneal edema and anterior chamber inflammation compared with conventional phacoemulsification cataract surgery.7 The PPC capsulotomy edge has also been shown to be stronger than that created by a femtosecond laser or manual CCC in paired cadaver capsulotomy-edge strength studies.8 Furthermore, initial experience in a small select group of patients has shown the device's ability to create complete, reproducible, and consistent circular capsulotomies.9 The average capsulotomy diameter is 5.5 mm.9 Placement of the device's optically transparent center on the corneal Purkinje image technically allows centration of the capsulotomy on the patient's visual axis; however, this is an approximation at best.

We report on our clinical experience with the Zepto PPC device in 100 consecutive patients having cataract surgery, focusing on the device's clinical safety, performance, efficacy, and cost-effectiveness.

PATIENTS AND METHODS

Study Design

A prospective consecutive case series of eyes that had anterior capsulotomy with the PPC device was performed at a single center in Tasmania, Australia. All surgeries were performed by the same experienced surgeon (B.J.V.) between June and July 2017. This was the surgeon's initial experience with the PPC device. The study was performed in accordance with the tenets of the Declaration of Helsinki; ethics approval was obtained from the Tasmanian Human Research Ethics Committee (H0016785). There were no exclusion or inclusion criteria, allowing assessment of the device's real-world capability and application.

Preoperative Assessment

All patients had a comprehensive baseline preoperative assessment including biometry, keratometry, and anterior chamber depth (ACD) measurements with an optical biometer (Lenstar LS 900, Haag-Streit AG); optical coherence tomography (OCT) (Cirrus HD-OCT, Carl Zeiss Meditec AG); Scheimpflug imaging (Pentacam AXL, Oculus Optikgeräte GmbH); specular microscopy (EM-3000, Tomey Corp.); and autorefraction (OPD-Scan III, Nidek Co., Ltd.). The rotating Scheimpflug camera's nucleus staging feature was used to objectively access cataract grading.10 Patient-specific IOL power was calculated using the Barrett Universal II formula.11

Surgical Technique

Before surgery, patients were instructed to instill topical ketorolac 4 times a day for the 2 days preceding the procedure. On the day of the surgery, topical anesthesia was administered and the pupil dilated with a gel formulation consisting of phenylephrine 2.5%, tropicamide 1.0%, cyclopentolate 1.0%, diclofenac 0.1%, and lidocaine 2.0%.

During the surgery, corneal incisions were made using a 2.4 mm keratome and 1.2 mm side-port blade. The anterior chamber was filled with sodium hyaluronate 3.0%–sodium chondroitin sulfate 4.0% (Viscoat). The thermal PPC device's nitinol cutting element was inserted into the anterior chamber through the 2.4 mm incision and positioned centrally on the anterior capsule. An assistant then applied suction to allow apposition of the nitinol ring with the capsule. Once adequate suction was achieved, as indicated by the console and reduction in the visible movement of small air bubbles through the tubing, electrical energy was discharged through the ring. Next, the assistant released the suction and the device tip was removed from the eye with the aid of a mushroom manipulator in the side port for countertraction. If a free-floating capsulotomy was not evident, the dimple-down technique12 was used to identify and address focal adhesions or tags. In eyes with broad incomplete capsulotomy attachments, the capsulotomy was carefully completed and removed in the usual CCC fashion with a capsulorhexis forceps.

The surgery was completed using standard phacoemulsification techniques and placement of a single-piece IOL in the capsular bag. Intraoperative observations and complications were recorded; these includes pupil stability, phacoemulsification time, balanced salt solution volume used, device performance, completeness of the capsulotomy, presence of tags, anterior radial tear, posterior radial tear, capsule rupture, lens dislocation, and corneal haze.

Postoperative Assessment

Postoperatively, patients were seen at 1 day and 3 weeks. At 1 day, patients had a full clinical assessment, anterior chamber flare photometry (FM-600 laser flare meter, Kowa Co., Ltd.), and corneal pachymetry. At 3 weeks, patients were clinically assessed again and had anterior chamber flare photometry, keratometry, OCT, corneal pachymetry, and specular microscopy. Endothelial cell density and the 3.0 mm central corneal thickness measured with specular microscopy and Scheimpflug imaging, respectively, were used to calculate the corneal volume stress index.13 After surgery, patients were prescribed topical ketorolac and dexamethasone 4 times daily for 4 weeks.

Outcome Measures

The main outcome measures were capsulotomy performance and intraoperative complications. Secondary outcome measures included the effective phacoemulsification time, intraocular pressure, postoperative inflammation, corneal edema, endothelial cell count, functional evaluation of the corneal endothelium, retinal thickness, cost-effectiveness, and early refractive outcomes. These secondary outcome measures were also compared with those of femtosecond laser–assisted cataract surgery and CCC from previously published datasets.14,15

Statistical Analysis

The data to be analyzed were imported into Stata 15 (StataCorp LLC) and examined with descriptive and frequency analyses. Categorical data were analyzed using the Fisher exact test, and continuous data were analyzed using the paired t test. Differences were accepted as significant at P values less than .05.

RESULTS

The study comprised 100 eyes of 88 patients (42 women [48%]) aged 53 to 95 years. Table 1 shows the patients' demographics and baseline characteristics. The Scheimpflug camera's nucleus staging cataract grading ranged from 0 to 5. The ACD ranged from (range 1.73 to 3.61 mm) and was less than 3.0 mm in 83 patients and 3.0 mm or greater in the remaining 17 patients.

Table 1
Table 1:
Baseline patient demographics.

Intraoperative Observations

The thermal capsulotomy device's silicone-encased nitinol cutting element was successfully inserted in all cases with relative ease and some counter stabilization of the globe. Satisfactory pupil dilation (>6.0 mm) before PPC device insertion was achieved in 94 eyes (94%). In 2 cases, a ring pupil expander (Malyugin Ring, Microsurgical Technology, Inc.) was implanted before insertion of the PPC device. One patient required the use of iris hooks after insertion of the device to avoid iris engagement during suction. In the remaining 3 patients, the PPC device was slipped under borderline-sized pupils without aids or interventions. In all cases, routine cataract surgery was successfully performed after PPC.

Device Performance

A complete free-floating capsulotomy was achieved in 70 eyes. Of the eyes with incomplete capsulotomy, 17 had small focal attachments, 7 had broad attachments, and 3 had both focal and broad attachments. Intended PPC treatment failed in 3 patients. Two of these were attributed to the assistant's failure to open the suction line to apply suction, and 1 was caused by faulty suction tubing. All 3 failed PPC cases were completed with a CCC and were excluded from further analysis. Table 2 shows the details of cases with an anterior capsule tear. No posterior capsule tears, intraoperative IOL dislocation, or corneal haze was observed. Table 3 shows the intraoperative observations/complications.

Table 2
Table 2:
Details of the cases with anterior capsule tear.
Table 2
Table 2:
Continued
Table 3
Table 3:
Intraoperative observations/complications.

Postoperative Observations

Postoperatively, a frayed appearance of the capsulotomy edge was noted on slitlamp biomicroscopy in most patients. The IOL was well centered with no cases of dislocation or subluxation. Table 4 shows the safety parameters measured in this study. Assessment of these parameters did not show safety concerns. Table 5 shows a comparison of these parameters with those of femtosecond laser–assisted cataract surgery and CCC.

Table 4
Table 4:
Baseline, intraoperative, and postoperative safety parameters.
Table 5
Table 5:
Baseline and postoperative safety parameter comparison.

DISCUSSION

We examined the clinical safety and performance of a thermal (precision pulse capsulotomy) device for creation of anterior capsulotomies in a prospective consecutive cohort. Previous studies of the PPC in cadaver and rabbit eyes found the device to be as safe as conventional phacoemulsification cataract surgery with improved capsulotomy tear strength compared with that of femtosecond laser–created anterior capsulotomy and CCC.7,8 In a previous small case series of 38 selected eyes,9 all eyes had successful free-floating capsulotomies with no complications. In our study, extensive testing of postoperative safety parameters did not raise important safety signals, and our findings are comparable with those we previously reported for femtosecond laser–assisted cataract surgery and phacoemulsification cataract surgery.6,14,15

The thermal PPC device was implemented at our practice without significant disruption to patient flow. The collapsible nitinol cutting element requires some countertraction/globe stabilization for insertion and removal, especially when smaller incisions (2.2 to 2.4 mm) are used. Once the device tip is inside the anterior chamber, the nitinol ring is released into its circular form in preparation for treatment. Device centration is first required, with intraocular movements of the device tip being somewhat counter to extraocular movement of the handle because the flexible tubing forms a pivot within the corneal incision.

A dilated pupil larger than 6.0 mm is necessary for performing anterior capsulotomy using the PPC device. In marginal pupils, the PPC device tip can slip under the pupil and successfully perform the capsulotomy; alternatively, standard pupil expanders can be used in conjunction. Of note, once the PPC device tip is inserted in the eye it cannot be reused; therefore, preplacement of pupil-enlarging devices is preferred.

Intended capsulotomy treatment failed in 3 patients in our cohort. In all 3 cases, the device tip was removed from the eye and anterior capsulotomy was completed using the conventional CCC method without further complications. Two of these cases were attributed to the failure of the assistant operator to open the suction line to apply suction, and 1 was attributed to faulty suction tubing. The PPC device in its current form is reliant on an extra operator to apply suction, energy, and release on instructions from the operating surgeon. This introduces a third-party variable to the surgical environment, which despite training and clear instructions cannot be entirely controlled by the operating surgeon and might affect surgical outcomes.

Despite a previous publication suggesting 100% success in delivering free-floating capsulotomies,9 complete capsulotomy was achieved in only 72% of our cohort. We observed focal attachment(s) in 17 eyes (18%), broad attachment(s) in 7 eyes (7%), and both focal and broad attachments in 3 eyes (3%). Based on our experience with femtosecond laser–assisted cataract surgery, all attachments were identified with careful inspection of the PPC capsulotomy margin and the use of adaptive surgical maneuvers.12,16 Once an attachment was identified, the capsulotomy was completed in the conventional CCC fashion. Although focal attachments behaved in a fashion similar to incomplete femtosecond laser–assisted cataract surgery capsulotomy and were easy to free using techniques such as dimple-down, broad attachments required careful completion in a more conventional CCC fashion because unlike with femtosecond laser–assisted cataract surgery, these broadly attached incomplete capsulotomy areas do not have preformed perforations. Incomplete capsulotomy and tags are well-known risk factors for capsule complications, such as anterior capsule and posterior capsule tear and rupture.3,6,16 Anterior capsule tear was identified in 4 eyes (4%) in our cohort (1 eye having 2 separate radial tears and intervening capsular tag). This is substantially higher than that in our cohort of femtosecond laser–assisted cataract surgery (15/804 [1.87%]) and CCC (1/822 [0.12%]).

This previously unreported high rate of incomplete capsulotomy and anterior radial tear in our patient cohort warranted further analysis. We did not find a relationship between ACD or axial length and capsulotomy outcome (either attachments or tears). Nor was there any evidence of learning curve effect when comparing our first 50 cases with the second 50 cases. In the first 50 cases, 31% of eyes (15/48) had incomplete capsulotomy compared with 24% (12/49) in the second 50 (P = .46). There were 2 anterior radial tear(s) in the first 50 eyes and 2 in the second 50 (P = 1.0). Incomplete capsulotomy and radial tears might represent complications arising from a common causal mechanism, or alternatively, complications arising from different or unrelated mechanisms.

We used Viscoat as the ophthalmic viscosurgical device (OVD) in our cohort of patients. This led us to postulate whether the rheological properties of the OVD used might be a factor in the incomplete capsulotomy or radial tear rates seen in our study. The PPC device is designed to evacuate the OVD from underneath the suction cup and oppose the capsulotomy ring against the capsule.9 In all our cases, the operating surgeon directly observed the flow of small air bubbles in the OVD through the PPC capsulotomy tip. Thermal energy was delivered only after cessation of the OVD flow, which often occurred up to a few seconds after the device indicated suction was complete. Viscoat is a dispersive OVD with a relatively low cohesion–dispersion index, meaning its small molecules act independently of one another rather than moving as a cohesive mass when exposed to low stress.17,18 These individual small molecules might have interfered with the suction of the PPC device engaging onto the anterior capsule, thereby impeding proper apposition of the cutting element with the capsule.

At the time of our study, no device manufacturer recommendation for optimum OVD use was provided. Based on our results, Mynosys investigated this issue and now recommends OVDs with a viscosity 300 000 mPas seconds or less. Interestingly, both Viscoat and Healon Endocoat (sodium hyaluronate 3.0%) (also a dispersive OVD used by Waltz et al.9 to achieve a 100% free-floating capsulotomy) have an identical viscosity of approximately 50 000 mPas.

An alternative theory is the differing electrical conductivity of the available OVDs. Viscoat might have a different electrical conductivity behavior than other OVDs, and this might influence the thermal delivery from the PPC device's nitinol element to the anterior capsule. A focal hotspot in the otherwise instantaneous thermal delivery through the nitinol ring to capsule might explain a focal weakness in the capsulotomy, leading to a radial tear.

Based on our experience with these radial tears and on personal communication from another surgeon operating at a different center who had reported 1 radial tear in 7 cases performed using the PPC device (all 7 cases with complete capsulotomy), we evaluated the ultrastructural features of PPC-created capsulotomy specimens and recently reported these findings.19 Although in general the capsulotomy specimens we examined were regular with smooth, rolled edges, as previously reported in animal and cadaver studies, some specimens had focal disruption of the capsule margin in what appeared to be thermal damage to collagen. Such focal disruption might indicate sites where radial tears propagate under intraoperative manipulative stresses. Regarding the influence of a dispersive versus cohesive OVD on the completeness of capsulotomy, we performed a further 10 PPC cases at our center with a 100% complete capsulotomy rate and no complications using sodium hyaluronate 1.0% (Provisc), a cohesive OVD. Further studies of the electroconductivity and suction of the PPC device in thermal delivery through the nitinol ring to anterior capsule are warranted, particularly for the various surgical OVD's available. We recommend using a cohesive OVD such as Healon or Provisc (both sodium hyaluronate 1.0%).

Further investigations by Mynosys based on our results also identified a variance of up to 10 μm in the diameter of the nitinol ring. This is believed to potentially cause an uneven distribution of energy throughout the cutting element. Improved quality-control measures were implemented to ensure consistency of the diameter of the nitinol ring.

An understanding of cost-effectiveness is also important with any new technology. A study using TreeAge analysis20 found a current added cost of approximately $150. If the radial tear rates are approximately 2%, the utility effectiveness of the device is reduced given the potential effect of radial tears on refractive outcomes. This renders the device not cost-effective, with an incremental cost-effectiveness ratio of approximately $150 000 per quality-adjusted life year (QALY). The incremental cost-effectiveness ratio is equal to the added cost of the product divided by the change in utility effectiveness from complications as indicated by the QALY gain. If the technology proves to be effective such that the theoretical benefit in effective lens position translates to a 5% improvement in visual outcomes, the incremental cost-effectiveness ratio improves to approximately $55 000 and a QALY gain of 0.01 is achieved. This translates to about 5 weeks of life if expectancy is 10 years.

As seen with femtosecond laser–assisted cataract surgery, technology evolution is paramount in increasing the safety and efficacy of a new surgical device. Elimination of a third-party operator, a more accurate suction mechanism and indicator, automation of the manual release system, enhanced nitinol ring flexibility, an altered setup process, and potential incorporation into the phacoemulsification systems are some areas that present opportunities for improvement of the thermal PPC device.

This was an uncontrolled case series of consecutive patients. The goal was to report the PPC device's real-world application. The secondary outcome measures were benchmarked against our previously published datasets on femtosecond laser–assisted cataract surgery and CCC and those of other publications. The eyes were not specifically matched for baseline characteristics, and differences might have existed between the population groups and their baseline characteristics.

In conclusion, the thermal PPC anterior capsulotomy device is capable of creating round, reproducible, appropriately sized capsulotomies. The incidence of incomplete capsulotomy in our case series was high (27%, with 10% being more significant broad attachments). Similarly, a corresponding high rate of anterior radial tear (4%) was identified and ultrastructural analysis suggests focal thermal damage can occur in some cases of PPC delivery. We recommend the use of a cohesive OVD because the rheological properties and electroconductivity of the OVD we used might provide explanation for these findings.

WHAT WAS KNOWN

  • Previous studies of the PPC in cadaver and rabbit eyes have shown the device to be as safe as conventional phacoemulsification cataract surgery with improved capsulotomy tear strength compared with that of femtosecond laser–created anterior capsulotomy and CCC.
  • A small case series of 38 selected eyes has also been reported, with 100% successful free-floating capsulotomies and no complications.

WHAT THIS PAPER ADDS

  • A high incidence of incomplete capsulotomy was found associated with the use of the PPC device. Similarly, a corresponding high rate of anterior radial tear was identified.
  • The use of a dispersive OVD might account for the high incidence of incomplete capsulotomy. This previously unreported high rate of incomplete capsulotomy and anterior radial tear in this patient cohort warrants further investigation.
  • A cost-effectiveness analysis found that the PPC device currently offers little additional value over a manual capsulorhexis.

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Disclosures:None of the authors has a financial or proprietary interest in any material or method mentioned.

© 2018 by Lippincott Williams & Wilkins, Inc.