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 Table of Contents  
REVIEW ARTICLE
Year : 2018  |  Volume : 56  |  Issue : 2  |  Page : 98-101

Zepto cataract surgery: The way forward


Department of Cataract and Cornea, M.N. Eye Hospital, Chennai, Tamil Nadu, India

Date of Web Publication6-Aug-2018

Correspondence Address:
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/tjosr.tjosr_51_18

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  Abstract 


Continuous curvilinear capsulotomy (CCC) is one of the most crucial steps of cataract surgery because of numerous surgical and anatomic advantages. The introduction of cataract surgery assisted by femtosecond laser has improved the repeatability and the accuracy of a perfectly rounded capsulotomy, as compared to the manual CCC. However, multiple surgical steps and the relatively high cost-per case have rendered this technology useful only to the affordable. This article describes a cost-effective and convenient new technique of perfecting the circular capsulotomy using a device called precision pulse capsulotomy or Zepto.

Keywords: Cataract surgery, complicated cataract, precision pulse capsulotomy, recent advances, Zepto


How to cite this article:
Madhivanan N, Nishanth S, Madhivanan N, Natarajan M. Zepto cataract surgery: The way forward. TNOA J Ophthalmic Sci Res 2018;56:98-101

How to cite this URL:
Madhivanan N, Nishanth S, Madhivanan N, Natarajan M. Zepto cataract surgery: The way forward. TNOA J Ophthalmic Sci Res [serial online] 2018 [cited 2019 Oct 16];56:98-101. Available from: http://www.tnoajosr.com/text.asp?2018/56/2/98/238495




  Introduction Top


Mastering the perfect manual capsulotomy is an art that requires experience and precision. Despite all precautions, human error even in the safest hands can lead to radial tears of the anterior lens capsule (ALC). It is well established that radial tears in the capsulorhexis increase the rate of cataract surgical complications.[1] Femtosecond laser is a good alternative to the manual capsulotomy, providing accurate and reproducible circular capsulotomies. However, there are several disadvantages to this technology, including prohibitive cost to a surgeon and a patient.

Mynosys (Fremont, CA, USA) has developed a novel capsulotomy technology called precision pulse capsulotomy (PPC) and trade named Zepto. PPC uses a highly focused, quick, multipulse, electrical energy discharge to produce a perfectly round anterior capsulotomy instantaneously uniformly along 360°.[2] This can be done during the normal sequence of the cataract surgery and is relatively priced lower than the femtosecond technology.

Capsulotomy is performed using a disposable handpiece with a soft collapsible tip and circular nitinol ring acting as a cutting element. The PPC Zepto device is introduced in the conventional surgical sequence after the keratome entry and anterior chamber filling with viscoelastic and can be centered on the visual axis to produce a capsulotomy of a predetermined diameter.


  Description of Precision Pulse Capsulotomy Device Top


The term Zepto was coined because, based on a metric scale, Zepto is 1 million times smaller than femto. This correlation can be extended to the small size of the instrument and the several millisecond speed of capsulotomy creation.[2]

PPC is performed using a disposable handpiece and capsulotomy tip called the Zepto that is connected to a control console for operation. The tip consists of a soft, transparent, silicone suction cup approximately 6 mm in diameter that houses a circular ring element made of the shape memory alloy nitinol. This nitinol ring element has been refined precisely at the micrometer scale to enable consistent and uniform 360° capsulotomies. The superelastic properties of nitinol allow the capsulotomy tip to be deformed mechanically into a narrower elongated shape for entry through a clear corneal incision of even 2.2 mm. This is achieved with the help of a push rod that comes from the disposable handpiece. Once the nitinol ring is pushed into the anterior chamber, the push rod is retracted. This allows the ring to reexpand automatically to its native circular shape within the anterior chamber.

The central portion of the suction cup is clear, allowing the surgeon to center the capsulotomy on the visual axis [Figure 1]. Once the position is confirmed, the surgeon applies the suction on the ALC, through a button on the central console. The use of suction delivered through the suction cup ensures optimal apposition of the nitinol ring with the lens capsule surface. Small amounts of tilt are compensated for automatically. With the suction firmly in place, the 360° capsulotomy is performed instantaneously at the touch of a button on the console. The intraoperative sequence of events is shown in [Figure 2].
Figure 1: Nitinol ring with the suction cup

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Figure 2: (a) Disposable handpiece is in its native circular shape at the start of the procedure. (b) Push rod is extended causing the capsulotomy device to assume an elongated shape for entry through the corneal incision. Capsulotomy tip handpiece is inserted through 2.2/2.8 mm corneal incision. (c) Surgeon retracts the pushrod, which allows the capsulotomy tip to naturally return to a circular shape. (d) The capsulotomy is performed by Zepto. Suction is reversed automatically. As the capsulotomy tip is manually withdrawn from the anterior chamber, the incision compresses the deformable tip to allow it to exit in its collapsed profile. (e) The completed circular capsulotomy by the precision pulse capsulotomy device.

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PPC is based on a rapid and precisely controlled method of tissue cleavage specifically developed for the efficient cutting of thin collagen membranes such as the human ALC. This precision pulse method uses the capsulotomy device's circular shape alloy nitinol ring element to convert a very brief train of fast electrical pulses efficiently over 4 ms (approximately 1 joule) into mechanical cutting energy. This occurs due to vaporization of the water molecules trapped between the ring edge and the microscopically stretched anterior capsule. This phase transition creates an instantaneous mechanical splitting of the anterior capsule along the entire ring circumference, resulting in a perfectly circular opening of a precise diameter. The extremely fast millisecond timeframe of PPC limits any heat dissipation beyond the layer of water surrounding the nitinol ring. The resulting cutting effect essentially is a mechanical one, similar to that of a manual tear. Unlike a manual or femtosecond laser capsulotomy (FSLC), however, the entire circumference of the Zepto capsulotomy is created at the very same instant because of the use of a circular conducting capsulotomy element. A circular capsulotomy is created, duplicating the shape of the circular nitinol element. The capsulotomy size is 5 mm in diameter, which may expand up to 5.25 mm after intraocular lens (IOL) placement.

Scanning electron microscopy (SEM) shows that the Zepto capsulotomy edge has a unique morphology characterized by an extremely smooth functional edge [Figure 3]. Detailed analysis revealed that Zepto not only creates a perfectly round, tag-free opening in the capsule but also at the same time places a microscopic eversion at the edge to present a small amount of the capsule underside for maximal edge integrity during surgery.[3]
Figure 3: (a) The cut edge (red arrow) and the microscopic, slightly everted functional capsulotomy edge during surgery (green arrow) are shown. (b) precision pulse capsulotomy — cut edge and the functional edge. (c) Higher magnification view of the rounded precision pulse capsulotomy functional capsulotomy edge (green arrow and bracket). (d) Manual continuous curvilinear capsulotomy (CCC) edge face. Although the precision pulse capsulotomy functional edge face [Figure 2c] is completely smooth, the CCC edge face [Figure 2d] is roughened with linear striations in the collagen matrix created by manual circumferential shearing forces. Picture courtesy Chang et al.[5]

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  Indications Top


PPC is a technology that is cost-effective and can be used in routine cataract surgeries of any grade and in premium IOL surgeries. Being able to center, the capsulotomy on the visual axis would be advantageous when implanting refractive lens implants such as extended depth of focus and multifocal IOLs.

It is a good option in complicated cases. PPC can be performed after insertion of iris expansion devices for small pupils. The tip is also designed with an angled lip in the suction cup to allow insertion of the device under the iris margin in the event of a smaller diameter pupil if necessary. It does neither cause any disruption to the iris tissue nor change in temperature of the iris tissue or the anterior chamber.[2]

Due to the mild suction effect of the Zepto, in cases of intumescent mature cataract with high intralenticular pressure, the Zepto not only performs a capsulotomy but also decreases the intralenticular pressure [Figure 4]. Further, there is no requirement for capsular staining to perform a PPC. Finally, PPC was successful in creating a circular capsulotomy in a case with 6 o’ clock hours of zonular dialysis.[4]
Figure 4: (a) Perfectly centered round CCC seen in retroillumination of a mature cataract. (b) Posterior chamber intraocular lens placed in the bag and centered where the edge of the lens optic is overlapping the Zepto rhexis margin

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Advantages

This device was developed through extensive testing in animal and human cadaver eyes with Miyake Apple view video imaging, showing insignificant zonular traction compared to manual continuous curvilinear capsulorhexis (CCC) while performing PPC in paired human cadaver eyes. These results also showed insignificant inflammation, endothelial cell loss, or heat detection when compared to manual CCC in the opposite eye.[5]

An important concern has arisen from published reports of an increased rate of anterior capsule tears following femtosecond laser capsulotomy.[6] SEM of FSLC anterior capsule buttons demonstrates a rougher edge when compared to manual CCC specimens. In addition, SEM analysis also reveals scattered aberrant laser shots that could be explained by microscopic eye movements occurring during the FSLC step.[6]

A study comparing the capsulotomy edge of PPC and femto and manual CCC with the help of paired cadaver eyes showed that the PPC edge was noticeably stronger and more resistant to radial tears compared to both manual CCC and FSLC.[3] This can be explained by the microscopic eversion of the capsulotomy edge, providing the integrity and the resistance to tearing [Figure 5].
Figure 5: Charts showing the capsule edge tear strengths in fellow eyes of the same pair in (a) precision pulse capsulotomy versus femtosecond laser capsulotomy comparison group, (b) the precision pulse capsulotomy versus CCC comparison group, and (c) the CCC versus femtosecond laser capsulotomy comparison group. Picture courtesy Thompson et al.[3]

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FSLC necessitates significant capital and per-case costs, slows the normal operative workflow, and cannot be used in small pupil. On the other hand, the PPC Zepto device is significantly cheaper, with less per-case cost, can be introduced during surgery in the conventional surgical sequence, can be centered on the visual axis to produce a capsulotomy of a predetermined diameter, and can be used in small pupils and mature cataracts with relative ease.

CE mark was obtained for this device in November 2015, and the US Food and Drug Administration approval was obtained in June 2017. Several places in India and abroad are now currently performing surgeries with this device, with a good track record.


  Conclusion Top


An ideal anterior capsulotomy would be continuous, circular, centered on the visual axis, maximally resistant to tearing, and of a precise diameter that circumferentially overlaps the IOL optic edge. Zepto or PPC — an inexpensive automated technology that could create such a capsulotomy consistently and reproducibly as an integrated surgical step, even in complicated cases — could thus be a valuable asset in a surgeon's armamentarium.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Carifi G, Miller MH, Pitsas C, Zygoura V, Deshmukh RR, Kopsachilis N, et al. Complications and outcomes of phacoemulsification cataract surgery complicated by anterior capsule tear. Am J Ophthalmol 2015;159:463-9.  Back to cited text no. 1
    
2.
Chang DF. Zepto precision pulse capsulotomy: A new automated and disposable capsulotomy technology. Indian J Ophthalmol 2017;65:1411-4.  Back to cited text no. 2
[PUBMED]  [Full text]  
3.
Thompson VM, Berdahl JP, Solano JM, Chang DF. Comparison of manual, femtosecond laser, and precision pulse capsulotomy edge tear strength in paired human cadaver eyes. Ophthalmology 2016;123:265-74.  Back to cited text no. 3
    
4.
Waltz K, Thompson VM, Quesada G. Precision pulse capsulotomy: Initial clinical experience in simple and challenging cataract surgery cases. J Cataract Refract Surg 2017;43:606-14.  Back to cited text no. 4
    
5.
Chang DF, Mamalis N, Werner L. Precision pulse capsulotomy: Preclinical safety and performance of a new capsulotomy technology. Ophthalmology 2016;123:255-64.  Back to cited text no. 5
    
6.
Abell RG, Davies PE, Phelan D, Goemann K, McPherson ZE, Vote BJ, et al. Anterior capsulotomy integrity after femtosecond laser-assisted cataract surgery. Ophthalmology 2014;121:17-24.  Back to cited text no. 6
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]



 

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Introduction
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