Crucial Steps I: Capsulotomy

19 Crucial Steps I: Capsulotomy


Mark Cherny



Summary


The capsulotomy is a most critical step in cataract surgery. Femtosecond laser allows great precision and consistency in forming capsulotomies. A thorough understanding of the capacities and limitations of the technology is required to form capsulotomies with the greatest precision. Techniques for dealing with small pupils, suction breaks, and interrupted treatments are described.


Keywords: femtosecond laser capsulotomy, optical coherence tomography, small pupil, Catalys, cataract, safety


19.1 Introduction


Trainees in cataract surgery are often taught that the creation of a capsulotomy is the foundation of a safe procedure. 1 Femtosecond laser–assisted cataract surgery (FLACS) has evolved with the objective of improving the precision and safety of multiple aspects of cataract surgery, including capsulotomy formation. 2 The author’s perspectives have been developed by using the Catalys system in more than 2,000 cases in the 3 years since July 2012. Since that time the author has planned all cases with FLACS, and has only needed to revert to standard phaco in four cases, due to postural issues, or extensive posterior synechiae.


19.2 History


Attempts to use laser to create a capsulotomy date back to at least 1998 when Geerling used a picosecond Nd:YLF laser (neodymium-doped yttrium lithium fluoride). 3


Animal studies of femtosecond laser capsulotomy size, shape, and strength 4 were followed by the initial clinical studies. 5


19.3 Principles


All femtosecond laser cataract systems have an imaging system, and software that assists detection of the anterior capsule. Manual adjustment options and confirmation safety checks are standard features.


19.4 Features of Available Commercial Platforms


Imaging systems are optical coherence tomography (OCT) based in the LenSx, Catalys, Ziemer, and Victus systems. The LensAR system has a Scheimpflug-based imaging system (▶ Fig. 19.1).



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Fig. 19.1 LensAR.


The LenSx system effectively unfolds the scan of the capsulotomy into a linear display, and this allows gates above and below the capsulotomy to be adjusted to ensure the capsulotomy is complete through 360 degrees. The SoftFit docking system, which was introduced in 2012 to replace the hard docking interface, is designed to reduce corneal distortion and folds that can translate into microtag and macrotag imperfections in the capsulotomy (▶ Fig. 19.2).



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Fig. 19.2 LenSx.


The Catalys system uses a liquid interface that avoids corneal distortion (▶ Fig. 19.1). 6


The Ziemer system is unique in the absence of any real-time view of the tissue. This may be disadvantageous because movement of the eye before or during treatment may not be visualized and could risk the capsulotomy being incomplete, misplaced, or associated with laser damage to other structures.


19.5 Theater Layout


The location of the femtosecond laser can impact the success of capsulotomy outcomes.


In some centers, it is located some distance from the operating room, and also well away from the anesthesia bay where regional blocks are administered. This creates a logistical incentive for the laser to be performed in advance of the anesthetic block in situations where blocks are used, and may create a logistical disincentive to the use of a block. As will be discussed, the use of regional blocks prior to laser delivery assists in globe stability and hence safety, particularly in some patient groups.


19.6 Patient Selection


Surgeons with access to FLACS have taken a variety of approaches to selecting patients for FLACS.


These include choosing patients based on the following:



The latter has been the author’s approach. In 2,200 cases, only 4 were excluded, due to kyphosis, narrow palpebral fissure, or extensive iris pigment adhesion to the posterior capsule. Patients with small pupils were not excluded, but a three-step technique described below was used. No pediatric cataract patients were in this series.


19.7 Patient Preparation


19.7.1 Pupil Dilation


Pupil dilation is critical to optimal capsulotomy formation. The author’s protocol includes the use of ketorolac 0.5% four times a day (quater in die [QID]) starting 3 days prior to surgery, and cyclopentolate 1% QID starting 1 day prior to surgery.


On arrival at the day surgery center, a premixed dilating gel formulation is instilled.


The preparation formulation is as follows:




  • Xylocaine 2% gel 1.5 mL.



  • Sixteen drops of phenylephrine 2.5% minims.



  • Eight drops of tropicamide 1% minims.



  • Eight drops cyclopentolate 1%.



  • Thirteen drops of Voltaren.


All the above is mixed, and drawn up into 0.2 mL doses for instillation into the conjunctival fornix.


This is supplemented by additional phenylephrine 2.5% or tropicamide 1% every 15 minutes for 1 hour, subject to the patient’s cardiovascular status. It is recommended to avoid phenylephrine 10% to reduce the risks of cardiovascular side effects.


Patients being treated at the beginning of an operating list may sometimes reach the laser room with less than ideal pupil dilation. It is advised that this issue be avoided by effective dilation protocols, assessment of pupil size on arrival, and expedited delivery of mydriatic agents. Admission nurses require specific education about this issue, and should be taught to use a pupil gauge to accurately measure pupil size and communicate immediately to the surgeon if a pupil is less than 6 mm 15 minutes after administration of the first dilating gel. Sometimes it is necessary to delay a patient’s treatment early on the list if the pupil is not 5.5 mm or greater in size. Patience on behalf of the surgeon is called for. While we are always anxious to commence the list, a short delay to gain adequate dilation can prevent major difficulties later.


19.7.2 Patient Mobility


In the author’s center, many patients having topical sedation can move to the laser room and theater by foot.


Patients having blocks move on a wheelchair, with nursing assistance to move to and from the laser bed and theater bed. This has proven to be a safe practice. Where possible, intravenous sedation is avoided at the time of block administration to facilitate safe transfer of the patient on and off the laser bed.


19.7.3 Positioning Patients


Patients must be comfortable, warm, and still for laser delivery. It is recommended to instruct patients as to what they will experience, and to explain that they must not move or talk for approximately 3 minutes once they have been positioned under the laser.


Patients with kyphosis or spinal fusion issues may be difficult to position under the laser. It is useful to use cushions behind the buttocks and waist. Elevation of the feet by up to 50 cm with an upturned basket and pillow almost always allows successful positioning. This can be time consuming; however, the time is usually well spent given that these are often patients with advanced cataracts, and are similarly hard to position in the operating room. Successful laser treatment aids greatly to the success and safety of the procedure once in the operating room in the author’s experience. These patients are often at the highest risks of complications such as vitreous loss, and prolonged surgery can be very difficult if the patient needs to be in an awkward posture for a long period. Hence, the use of FLACS is strongly recommended in such cases to maximize the safety of the procedure.


19.7.4 Anesthesia


Approximately half my patients have topical anesthesia, and half have a regional block prior to laser delivery. Occasionally some patients booked for topical anesthesia require conversion to a block because they lack sufficient capacity to keep the eye still and fixated on a target once docked to the laser. In these cases, the author undocks them, and asks the anesthetist to block the administration, either on the laser bed, or in the recovery bay, prior to returning for the laser delivery.


It is critical to avoid lasering a patient if the patient has an overly tight orbit due to excessive use of anesthetic in the orbit, or if there has been an orbital hemorrhage. These situations are best managed by deferring or canceling the treatment. Proceeding with the laser compels you to open the eye, and deal with an unpredictable and hostile operating environment, where complications such as capsular tears, dropped nuclei, vitreous loss, and choroidal or expulsive hemorrhages will be more likely than usual.


19.8 Communicating with Patients


Clear preoperative instructions on the anticipated patient experience are helpful.


It is recommended to reinforce the instructions to




  • Avoid speaking.



  • Avoid moving.



  • Fixate the target light.


Knowing how much to talk to patients during the 2 to 3 minutes of engagement with the laser system is a skill worth refining. The author finds a few words of reassurance and a reminder of the key instructions at the commencement of docking work best for most patients, followed by silence until the treatment is over. This avoids the tendency for the patient to acknowledge any verbal communications with a nod or vocal response, either of which can disturb accurate laser delivery by the associated facial movements.


Occasionally, we find that very anxious or claustrophobic patients require a nonstop verbal commentary from the surgeon to feel most at ease. The author tries to speak to them in a way that they need not respond to.


19.9 Capsulotomy Size


The author’s preferred capsulotomy size setting is 4.8 mm. This gives a constant overlap of the optic in the range of 0.4 to 0.8 mm for most implants. Rarely does the author reduce this if the pupil dilation is at the range of 5.0 to 5.5 mm. The smallest capsulotomy size the author will use is 4.1 mm.


In patients whose pupils will not dilate beyond 5 mm, the author inserts a Malyugin ring prior to performing the laser. This is called a “three-step procedure,” given the treatment starts in the theater, moves to the laser room, and then back to the theater. This technique is detailed below.


19.10 Capsulotomy Centration


The systems have different capacities to choose the centration of the capsulotomy (▶ Fig. 19.3).


Most Catalys users have found optimal centration of the capsulotomy on the intraocular lens (IOL) by choosing the “scanned capsule” option for centration. The Catalys software analyses the imaged sections of the anterior and posterior capsules and extrapolates these to identify the theoretical equator of the capsular bag. Given that theoretically the IOL will settle into the equator symmetrically, this should lead to the capsulotomy symmetrically centering on the IOL. The author’s observation is that this technique works with extremely high predictability (▶ Fig. 19.4).


If an error signal occurs due to the capsulotomy being within 500 μm of the pupil margin, it can be rectified by reverting to a pupil-centered capsulotomy (▶ Fig. 19.5).



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Fig. 19.3 Intended capsulotomy after programming on the Abbott Catalys. (a) Infrared view. (b) Optical coherence tomography view. (c) Completed.




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Fig. 19.5 (a) Scanned capsulotomy centration causing error signal due to encroachment within 500 μm of pupil. (b) Switching to pupil-centered capsulotomy overcomes error signal.


19.11 Duration of Treatment


Treatment durations can be measured in a variety of ways.




  • Time for the patient in the laser room.



  • Time for the surgeon in the laser room.



  • Time under dock.



  • Duration of capsulotomy treatment.



  • Duration of entire laser delivery.


The time for the patient in the laser room can be as long as 15 to 20 minutes, but much of this can be time transferring the patient to and from the bed into a comfortable position, and waiting for the surgeon to arrive. Often it is only 5 minutes.


The time for the surgeon in the laser room is of significance as it reflects the impact on patient flow that the laser technology has on surgeon and operating room productivity. This impacts on the economics of the technology, affecting both the surgeon and the hospital facility. It also has a bearing on how successfully the laser machine can be shared between two or more surgeons conducting operating lists simultaneously in the one theater suite. Initially this interval sometimes measured up to 10 minutes during our primary learning curve and working with the first generation of software. It is now usually less than 5 minutes. Time has been saved by increasing efficiency in obtaining and maintaining successful docking of the patient interface, and improved software speed and usability. In recent months the author has not been performing any laser delivery to the cornea for incisions or astigmatic treatments, and that too has decreased the duration of treatments.


“Time under dock” is the period starting with suction of the patient interface device (PID) on the eye, and terminating when the suction is concluded, usually at the completion of the treatment. This is currently 2 to 2.5 minutes with the author’s technique and settings. Variability occurs if there is a need to repeat the OCT scanning, and depends on pupil size and on the volume of the lens being treated.


Most capsulotomies with the Catalys can be achieved with 1 to 2 seconds of laser delivery.


19.12 Confirmation of Imaging


The Catalys system provides OCT cross-sectional imaging of the anterior segment viewed in two planes at right angles, and also real-time infrared imaging of the anterior segment. The system uses autodetection algorithms to detect the key anatomical features:




  • Anterior cornea (on the OCT).



  • Posterior cornea (on the OCT).



  • Anterior lens surface (on the OCT).



  • Posterior lens surface (on the OCT).



  • Pupil margin (on the infrared image).


Critical to the success of the treatment is accurate correlation of these structures as identified by the software, with the true position of the structures at the time when the laser is delivered. It is essential that the correct anatomical identification is confirmed by the surgeon. The machines’ algorithms have limitations, particularly in unusual circumstances (▶ Fig. 19.6).



In ▶ Fig. 19.7, there is a deficiency of zonular support in a case of congenital spherophakia, which was not diagnosed prior to surgery. This resulted in a subluxation of the lens into the anterior chamber when under dock for FLACS. The software has incorrectly identified the position of the anterior capsule. The abnormality was identified by the surgeon, and FLACS (▶ Fig. 19.7).



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Fig. 19.7 Optical coherence tomography image of lens subluxed into anterior chamber.


One of the key tasks of the surgeon is to monitor for movement of the globe in the X–Y plane.


There is often slight movement of the globe in relation to the PID after docking, particularly if topical anesthesia alone is used, but movement can sometimes be seen even if a regional block has been applied, due to residual extraocular muscle function, and the small amount of movement of the globe that can occur relative to the limbal conjunctiva to which suction is applied.


The attachment of a small light-emitting diode (LED) to the laser housing in front of the contralateral eye aids greatly in achieving optimal stability of the treated eye. As the patient swings under the laser housing, the patient is reminded to “look at the green light in front of the eye we are not treating.” Once the imaging starts, if there is any movement of the eye being treated, the patient is reminded to “Look at the green light.” At this point, it is often possible to see a re-fixation movement of the eye being treated, which then becomes quite still. The technician then activates the “rescan” button, and the OCT scan is recommenced, with the eye in a stable position (▶ Fig. 19.8).


Feb 23, 2020 | Posted by in OPHTHALMOLOGY | Comments Off on Crucial Steps I: Capsulotomy
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