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3 Supported by unrestricted educational grants from Abbott Medical Optics, Alcon Laboratories, and Bausch + Lomb on the machine. The foot pedal controls the stroke length, which may be longitudinal, transverse, or torsional. Fluidics refers to inflow and outflow (Figure 1). "Your flow is your attraction to the phaco tip," Dr. Burger said. Outflow has 2 components: aspiration of the material—the amount of flow through the tubing—and the vacuum, the attachment of the fragment to the tip. Phacoemulsification units rely on 2 types of pumps—peri- staltic and venturi (Figure 2). The chamber and IOP increases even with the same pump rotation, increasing the vacuum in the aspiration flow line. With total occlusion, the IOP is mandated totally by the bottle height, and the vacuum reaches the maximum preset level. Flow largely controls distal followability, Dr. Cohen said. The surgeon can increase the pump rate to bring pieces to the phaco tip or bring the aspiration port closer to the piece in foot position 2, increasing the effect of flow, he explained. "Proximal followability is controlled mostly by vacuum and somewhat by flow," he said. With partial occlusion, the flow in the anterior chamber decreases, but with the greater differential be- tween the pressure in the anterior chamber and aspiration flow line some vacuum develops. With a flow pump, surgeons perform partial occlusion phaco, or carouseling phaco, he said. "Initially we have occlusion of the phaco tip with the nuclear fragment in foot position 2, and the fragment is engaged. Then we go to foot position 3, and we have an ultrasound cycle, which par- tially breaks down the fragment." There is some flow and some vacuum. peristaltic pump usually uses tub- ing to milk out the fluid. Vacuum is occlusion dependent and rises more slowly. "In the venturi sys- tem, a compressed air system, your vacuum is occlusion independent and will more rapidly rise," she said. Most modern machines use software to mimic both. "There's an incredible power to very small and intentional adjustments to your settings in keeping patient satisfaction at that postoperative visit as high as possi- ble," Dr. Burger said. PERISTALTIC VENTURI Vacuum Rapid Rise Occlusion Independent Pump Slower Rise Occlusion Dependent Modern phaco machines combine the basic principles of both "When the phaco has par- tially broken it down, it aspirates the emulsate, and it gets the frag- ment to carousel with proximal followability into your phaco tip so that you now have occlusion, and this whole cycle can start again," Dr. Cohen said. Ultrasound modulation "Our goal is to remove a cataract using enough power to be effi- cient, but not using more power than necessary," said Lisa Park, MD, associate professor and associate director of residency training, Department of Oph- thalmology, New York University School of Medicine. This reduces the risk of thermal injury, corneal swelling, and endothelial cell loss. Power modulation improves followability with less chatter, she explained. Direction variables include longitudinal, transversal, and torsional phacoemulsification options. Timing includes con- tinuous, pulse, and burst modes (Figure 3). The hyperpulse mode delivers more than 100 pulses per second, and hyperburst results in a burst duration of 4 ms. "You would … change your settings according to the objective of what you're trying to accom- plish, and you'll modify your setting according to the density of the nucleus you're trying to remove," Dr. Park said. Figure 3. Ultrasound power modulation Source: Lisa Park, MD continued from page 1 Figure 2. Comparison between peristaltic and venturi pumps Source: Berdine M. Burger, MD

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