New technology for preocclusion surgery

To utilize innovative phacoemulsification platform features, surgeons must understand the primary components of phaco machines and the intended phaco procedure. These components are the density of the nucleus being emulsified and the planned phaco procedure. Although individual surgeons will develop a technique that efficiently debulks the nucleus and aspirates the fragmented pieces, the primary surgical approaches are the “divide and conquer,” the “stop and chop,” and phaco chop.

Using fluidics to avoid capsular tears

William J. Fishkind

The surgeon moves lenticular fragments from the plane of the capsular bag to the plane of the iris for emulsification. Phaco is now performed at the iris plane, where the procedure can be performed more quickly and with less risk to the patient. In the past, phacoemulsification was performed down in the capsular bag, close to the posterior capsule or at the lens equator, where phaco energy can be damaging. Phacoemulsification performed under the anterior capsule near the equator increases risk because it is easy to tear the capsular bag. In my own experience, I have found a 60% incidence of capsular tears in phaco, about 30% irrigation and aspiration (I&A), and the remainder in other stages of cataract surgery.

Therefore, surgeons can utilize occlusion to elevate nuclear fragments to the iris plane where they are emulsified in the mid-pupil. This was dangerous in the past because high power at the pupillary plane was prone to damage both iris vessels and endothelium. However, with new power modulations the power necessary for emulsification is minimal and less damaging to delicate tissues. Fusion Fluidics technology in the WhiteStar Signature System (Advanced Medical Optics [AMO]), the ability to choose a venturi pump or peristaltic pump instantaneously will allow the use of venturi pump responsiveness to assist in occlusion and elevation of the fragments with essentially no lag time. Once elevated to the iris plane, the nuclear fragment is emulsified after an immediate change to the peristaltic pump for more controlled rise times and flow rates. With this advanced technology, it is possible to aspirate fragments in the iris plane with low power and low to moderate vacuums and flows, while maintaining a stable anterior chamber.

Nuclear density

The density of the nucleus will impact the likelihood that a capsular tear will occur. Tears are common when operating on soft nuclei because they are difficult to chop and lift, forcing the surgeon to aspirate lenticular pieces at the bag equator. This technique is hazardous because it threatens the integrity of the equatorial capsular bag. Capsular tears are also common when operating on a hard and thick nucleus. While removing a mature nucleus, sharp fragments can be pushed against the capsular bag. This occurs when, working within the confines of the capsular bag, the surgeon positions the phaco tip close to the posterior capsule so that when an occlusion with a postocclusion surge occurs, the sudden anterior movement of the posterior capsule allows it to compress around a sharp fragment of nucleus, or be emulsified by the phaco tip. A capsular tear results.

Early capsular tears associated with a hard nucleus present a difficult clinical environment. Depending on location, timing, and whether vitreous face is intact or ruptured, capsular tears can set off a series of adverse events. If the capsular tear occurs early in the procedure, with a large or hard nucleus the surgeon must be careful not to enlarge the tear, rupture the vitreous face, or lose the nucleus. Conversely, a small puncture in the posterior capsule that occurs at the end of surgery is not a major complication.

Vitreous is clearly a complicating factor. If vitreous is not present during the procedure, the capsular tear will have a lesser impact than if vitrectomy is required. Additionally, the volume of vitreous removed has an effect on outcome. In general, once a surgeon detects a capsular tear, an attempt to complete the surgery while minimizing damage is obviously indicated. However, if the tear occurs early in the surgery, and the nucleus is hard, it may be prudent to choose to close the corneal wound, create a new scleral incision, and remove the nucleus by controlled, extracapsular extraction.

The mechanics of moving fragments

Fluidics created by the pump is the primary force used to maneuver the fragment. Power created by ultrasonic generators is the force used to emulsify the fragments. Phaco power is defined as the aggregate of jackhammer energy, or the physical striking of the needle against the fragment; and cavitational energy is defined as the creation of ultrasonic microbubbles. The microbubbles implode and create a shock wave that is emitted from the phaco tip, impacting nearby material, and emulsifying it. In general, the jackhammer effect has a more significant importance because it takes place over the throw of the needle, for about 0.4 mm vs. cavitational energy, where the effect is measured in microns. However, both types of energy contribute to the removal of the nucleus.

Cavitational energy has two components, transient cavitation and stabilized cavitation. Transient cavitation is the powerful development of microbubbles imploding with subsequent shock waves. After a short time, approximately 4 ms, the bubbles continue to vibrate but have no effect. At this point, the energy becomes stabilized cavitation. This form of cavitation is to be avoided because it is a waste of energy. The best way to perform phaco is to maximize the jackhammer and transient cavitational energy and avoid stabilized cavitation.

Innovation was linked to the recognition that occlusion created surge and the best way to prevent it was to prevent occlusion altogether. —William J. Fishkind, MD

Fluidics, the other major force used during phaco surgery, consists of flow and vacuum. Flow controls the speed at which fragments come to the phaco tip and is measured in cubic centimeters/milliliters per minute. Vacuum determines how securely material is held once occlusion occurs and is measured in millimeters of mercury. With a peristaltic pump, occlusion is necessary to develop vacuum. In the past, a surgeon would skewer a fragment on the phaco tip and allow vacuum to build to its preset maximum. At that point, with the introduction of phaco power, the nucleus would be emulsified. The instant of emulsification would allow potential energy in the aspiration tubing and the high potential vacuum to aspirate fluid from the anterior chamber faster than inflow from the irrigation bottle could replenish it. The sudden outflow of fluid would inevitably create a surge. The result of the surge would be shallowing of the anterior chamber and trampolining of the posterior capsule. If occlusion is defined as occurring at this given moment, this type of phaco would be considered postocclusion phaco.

The period during which the fragment is close to the tip, but not specifically creating occlusion, is defined as preocclusion. The moment of occlusion, when the fragment blocks the phaco tip, is defined as occlusion. Finally, surgical activity occurring after phaco energy is applied and the cataract is broken up is called postocclusion. Traditionally, surgeons performed phacoemulsification in occlusion and postocclusion, with the inevitable consequence of postocclusion surge. Not only does surge create potential problems with phaco, but it also destabilizes the vitreous. Whenever the chamber is allowed to collapse, the vitreous moves anteriorly, creating traction on its points of attachment, including the macula. The potential result is cystoid macular edema.

Surge historically was the cause of complications, but surgeons had no other option because their equipment supported postocclusion phaco. Understanding this, the phaco platform designers developed new technology, such as pumps with faster response times, in an effort to minimize surge. However, innovation was linked to the recognition that occlusion created surge and that the best way to prevent surge was to prevent occlusion altogether. This concept was first introduced with the development of the WhiteStar Technology. It has been refined with the introduction of the Signature System with Fusion Fluidics.

The power of preocclusion phacoemulsification

The phaco power component of the WhiteStar Technology has two elements. These elements are defined as the “duty cycle.” The power-on segment consists of micropulse of power combined with a brief power-off cycle, both of predetermined duration. A duty cycle is adaptable, for example, with 4 ms off and 8 ms on, resulting in a 12-ms duty cycle. It could also be divided into 6 ms on and 6 ms off or 8 ms on and 4 ms off, depending on surgical goals.

The development of micropulse phaco is a revolutionary improvement. The short burst of aspiration without power will attract the fragment of nucleus to the proximity of the phaco tip. The tip then energizes, creating emulsification of the fragment. The emulsification energy is so brief that only partial occlusion of the tip occurs, therefore, there is no postocclusion surge. Micropulse phaco produces the ability to perform phaco in the preocclusion half of the occlusion algorithm. Therefore, there is no surge.

Pulse-shaping technology

The next innovation in the WhiteStar Technology model was the creation of the increased control and efficiency (ICE) system. ICE is a predetermined “kicker” at the beginning of the power pulse. This burst of energy can be programmed to be up to 7% of the total energy of the pulse and can be constant, increased, or decreased throughout the pulse. In theory, this pulse repels the material from the phaco tip ever so slightly. By repelling it for a millisecond, it permits fluid to fill the void around the phaco tip, thus enhancing transient cavitation (Figure 1). The fluid must be replenished because it is a catalyst for microcavitational energy.

By repelling material from the phaco tip for a millisecond, the pulse permits fluid to fill the void around the phaco tip, enhancing transient cavitation —William J. Fishkind, MD

ICE, therefore, is a form of pulse-shaping technology. Other platforms, such as the Stellaris Vision Enhancement System (Bausch & Lomb), have pulse-shaping modes, whereby they curve the rising energy pulse in an effort to hold the material adjacent to the phaco tip without permitting occlusion to occur, thus creating the preocclusion environment.

In my opinion, the most significant development in phaco technology in the past 5 years is the advance from postocclusion phaco to preocclusion phaco. Earlier attempts to standardize preocclusion phaco include the ABS (aspiration bypass system, Alcon) tip, which did not exactly create preocclusion but gave the surgeon more time to react, and the Legacy with Advantec NeoSoniX (Alcon). Later advances include torsional phaco, which is ultrasonic preocclusion phaco, and molded sound waves used in the Stellaris system.

Micropulse phaco is the prerequisite for preocclusion phaco. Another method is torsional phaco. The torsional (oscillatory) movement of the phaco tip does not allow the fragmented material to occlude the phaco tip. Therefore, torsional phaco creates a “magnetic” attraction of nuclear fragments to the phaco tip while diminishing the creation of surge. AMO has created a similar approach with the development of elliptical phaco.

For surgeons who have a preference for occlusion, the WhiteStar Signature System with Fusion Fluidics can provide high vacuum and high flow with the venturi pump. The maximum rates are 650 mm Hg vacuum and 60 mL/min of flow. Surgeons who prefer occlusion phaco can modify postocclusion surge by making use of Signature’s Chamber Stabilization Environment (CASE) to prevent surge. In an example of a 500-mm Hg vacuum and a 45-mL/min flow, the amount of surge measured using CASE parameters is 56% less than that without CASE. CASE can be used in postocclusion surgery to decrease surge.

Pulse-Shaping Technology Figure 1. Millisecond bursts prevent cavitational energy from stabilizing and avoid occlusion. Source: Advanced Medical Optics

CASE technology

CASE technology allows a surgeon to determine vacuum levels based on clinical conditions. The surgeon presets an “up” threshold. When the pump reaches that maximum, it slows down or stops for a preset period, and then increases again (Figure 2). For example, if a surgeon is performing phaco on a soft nucleus aspirating the equatorial material, it would unfortunately be common to aspirate adherent equatorial capsule, leading to a capsular tear. However, with this software, when the phaco tip aspirates a piece of material and vacuum builds to the preset level, a chime alerts the surgeon. The software recognizes the vacuum level on the up threshold and slows the pump. Before the phaco tip can aspirate the attached capsular equator and tear it, the pump stops, thus releasing the cortex and capsule preventing a capsular tear. The fastest reaction time of a surgeon has been timed at approximately 20 ms.¹ In general, I can respond to a visual signal in about 20 ms. The equipment’s reaction time is about 1/10 ms. This is almost instantaneous. CASE therefore improves the safety margin to prevent capsular tears by approximately 200%.

These technological tools allow surgeons to be confident during surgery because they know the equipment’s functions and protective features. My posterior capsular tear rate has dropped from 1.5% before micropulse phaco to 0.5% after micropulse phaco. Now, with micropulse, CASE, and all of the added features, I believe it has dropped to about 0.1%, and continues to decrease. These exceptional outcomes are critical because the expectations of patients continue to increase. Our patients expect emmetropic outcomes. We must perform capsular bag cataract surgery rather than vitrectomies. Finally, the addition of advanced technology IOLs have added to the demands for extraordinary surgical outcomes

CASE Technology Figure 2. Surgeons can preset vacuum level "up" threshold and "down" threshold depending on clinical conditions. Source: Advanced Medical Optics

Learning curve becomes an exploration

The learning curve with the WhiteStar Signature System with Fusion Fluidics dictates that the user define a phaco parameter starting point. This point of entry can be the parameters of a selected phaco surgeon whose settings can be downloaded with the assistance of a laptop computer or an equipment technician who has knowledge of the machine can program and modify the system. The company specialist is adept at adjusting the flow and vacuum as well as adjusting the duty cycles on the WhiteStar Signature system. They can adjust the ICE, the CASE, and any other features. In about a month, a surgeon will have developed enough experience to evaluate the performance of the selected settings and make adjustments that reflect his or her technique.

I have completely changed my phaco technique since the introduction of this new technology platform. I perform phaco-chop surgery, even on soft nuclei. I attempt to chop the soft nucleus in half and then remove each heminucleus separately, doing the majority of phaco at the plane of the iris. Previously, there was too much power that could damage the iris and the blood aqueous barrier, as well as the endothelium. Now, with low power, more control, and less surge, I can perform phaco in the plane of the iris without causing any problems. I carry out the entire phaco procedure far from the posterior capsular bag, which also helps reduce my posterior capsular tear rate. This new machine with its sophisticated phaco parameters has facilitated my surgery.

Surgical media center and on-screen display

Surgeons interested in the scientific or academic aspect of phaco surgery can use the surgical media center, which can be programmed to monitor numerous surgical parameters and present them in a user-friendly manner. The data output viewed on a computer monitor is presented in a straight forward manner and the entire clinical case, both video and commanded surgical information, can be downloaded for later analysis. The surgeon can therefore identify specific problems that occurred during the surgery—such as the inability to hold a piece of nucleus—replay the video of that segment of the surgery and analyze power, flow, vacuum, CASE, or other selected values and learn from the problem.

I find that the surgical media center also makes WhiteStar Signature System with Fusion Fluidics an excellent tool for surgeons who teach. The video combined with an assortment of phaco settings displayed in multiple formats allows for analysis of advanced phaco concepts with on-screen display substantiating the academic theory.

The on-screen display and user interface has been much improved from previous machines making it more intuitive. It gives voice confirmation of settings, and it is easy to input changes and supervise settings. Moreover, settings can be changed quickly and without much difficulty. The Bluetooth wireless foot petal is also a benefit because it can be moved anywhere.

Conclusion

In my experience, once assembled and programmed, technologically advanced equipment such as the WhiteStar Signature System improves surgical technique, increases procedure safety, and enhances surgical outcomes.

Reference

1. Data on file. Santa, Ana, CA: Advanced Medical Optics, Inc.

William J. Fishkind, MD, FACS, is codirector of Fishkind and Bakewell Eye Care and Surgery Center, Tucson, AZ, and clinical professor of ophthalmology at the University of Utah, Salt Lake City.