In the past few years, with the advent of micropulsed phacoemulsification, surgeons have begun removing lenticular fragments before occlusion can occur, a strategy I call preocclusion phacoemulsification, or POP technique. Today's micropulsed phaco technology can be programmed to halt occlusion surge, which causes a sudden shallowing of the anterior chamber that may lead to tearing of the capsule and vitreous face. Thus, the POP technique can increase the safety of the procedure.
Many types of phaco tips on the market can be used for the POP technique. What sets this technique apart from others is the use of short, micropulsed bursts of ultrasonic power, which essentially holds the fragment of cataractous material thousandths of a millimeter away from the phaco tip. As a result, occlusion rarely occurs, and, therefore, neither does surge.
Advanced Medical Optics, Inc. (Santa Ana, CA), recently upgraded the safety features of its Whitestar ICE (Increased Control and Efficiency) software for the Sovereign phacoemulsification system. Employing the upgraded safety features of advanced pulse shaping and Chamber Stabilization Environment (CASE) in a POP technique minimizes vacuum rise, delivers less phaco power to the anterior chamber, and allows for greater surgical control (Table 1).
WHITESTAR ICE PULSE SHAPING
Molding Ultrasonic Waveforms
Until now, ultrasonic waveforms have been on and off. At first, they were on and off for long periods, ranging from 50 to 150 milliseconds. Then, we advanced to individually adjustable micropulsed technology, and the permutations have become infinite. We now have a duty cycle consisting of a period of on power and periods of off power as brief as 4 milliseconds.
With Whitestar ICE, surgeons can mold an ultrasonic waveform. The software allows the ophthalmologist to vary the duration of the pulse power and then add a burst of energy at the beginning of the ultrasonic wave to provide a kick at the beginning of each burst (Figure 1). By physically separating nuclear material from the phaco tip, this kick creates a microvoid between the almost occluded tip and the nuclear material. The kick is designed to jumpstart the cavitational aspect of emulsification without compromising followability. It generates more emulsification power with less energy, thereby ensuring the POP technique.
The kick also allows the surgeon to craft that burst of power for as short or as long a duration as desired. One can keep the kick constant across the phaco power range or change it such that it rises and falls as power increases. The direct result of this programmable feature in Whitestar ICE is improved cutting efficiency, especially in soft nuclei. Energy in the eye remains low but still imparts magnetic followability to nuclear fragments.
New pumps on phaco systems are what I call hybrids. It does not matter if they mechanically look like peristaltic or venturi pumps. Surgeons can program hybrid pumps to encompass the characteristics of both the peristaltic and venturi. For example, the Sovereign has what looks like a peristaltic pump, but it can ramp up vacuum slowly or quickly, stop, or even go backwards. One may program the pump to hold the vacuum at a preset amount or to change the rise time and vacuum level after reaching a preset value.
With the latest software, the surgeon can adjust the pump's ramp speed to modify the rise time. The ability to alter the rise time and to use the Whitestar ICE kick is a powerful combination. The surgeon now can set the vacuum a little higher than previously and then adjust the rise time to be little bit longer. In this scenario, the vacuum increases a little more slowly, thereby enhancing one's ability to bring lenticular material toward and hold it on the phaco tip without reaching the preset maximum vacuum and, therefore, never creating occlusion. By enhancing the POP technique and thus reducing surge, the Sovereign allows for more stable chambers than previous versions of the technology.
CASE is an automatic control feature that monitors vacuum during phacoemulsification. Designed for enhanced chamber stability, this feature actually reduces vacuum power when occlusion occurs, maintains particle-holding power, and resets the maximum vacuum when occlusion ceases. The surgeon sets the vacuum for CASE at the desired level. Once reached, the vacuum is held for 200 milliseconds. If occlusion does occur, the software can adjust the phaco vacuum and should thus avoid inadvertent damage to the capsular fornix when phacoemulsification occurs near the capsular equator.
Modifications to the Sovereign system's software help cataract surgeons to perform phacoemulsification efficiently and to deliver less power to the anterior segment. The POP technique and Whitestar ICE should enhance the stability of the anterior chamber and thus reduce the incidence of torn posterior capsules and complications.
William J. Fishkind, MD, FACS, is Co-Director of the Fishkind and Bakewell Eye Care and Surgery Center in Tucson, Arizona, and Clinical Professor of Ophthalmology at the University of Utah in Salt Lake City. He is a consultant to Advanced Medical Optics, Inc. Dr. Fishkind may be reached at (520) 293-6740; firstname.lastname@example.org.