AUG 2014

EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.

Issue link: https://digital.eyeworld.org/i/357599

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Page 68 of 82

T he evolution of modern cataract surgery is exciting because of rapid technologi- cal advances that now allow surgeons to modify phaco settings in order to increase patient safety and decrease healing time. The trend has been to minimize phaco energy in order to protect corneal endothelial cell loss, and an understanding of power modulation is an important step toward achiev- ing this goal. There are two basic principles to consider regarding power modula- tion: the direction of phacoemulsifi- cation—longitudinal, transversal or torsional—and timing—continuous, pulse, burst, as well as hyperpulse and hyperburst. Longitudinal, transversal, torsional phacoemulsification Traditional longitudinal phaco uses a jackhammer-like motion, in which the tip moves forward and backward. However, it has been recognized that when the tip moves backward, energy is being produced but not breaking up the lens, re- sulting in unnecessary heat produc- tion. With transversal ultrasound, longitudinal phaco is combined limited to 20 pulses per second, but hyperpulse can allow for greater than 100 pulses per second. Similar- ly, hyperburst can be programmed to a very short burst of 4 ms com- pared to regular burst mode of about 80 ms. Both options can be helpful in limiting phaco energy and heat delivered. Adjusting settings for surgical objectives As surgeons, we must change our settings depending on the type of case. With a typical 2+ or 3+ nucle- us, I use 100% torsional phaco on a linear setting. I have found that this mode generates very little heat and allows for very clear corneas on post- op day 1, even with a supracapsular approach, which is what I favor for a soft lens. In contrast, with a very dense lens, I will lower the torsional parameters and increase longitudinal phaco to a maximum of 40% and add pulse at a 35% duty cycle with 10 pulses per second. In all cases, the goal is to phaco only when there is complete occlusion at the phaco tip, to minimize unnecessary energy. Understanding the options for power modulation allows a surgeon to decrease energy production, reduce endothelial cell loss, resulting in more efficient surgery, clearer corneas, and ultimately better patient outcomes. Dr. Park is clinical associate professor and associate director of residency training, Department of Ophthalmology, New York University School of Medicine, New York. She can be contacted at Lisa.Park@nyumc.org. Lisa Park, MD by Lisa Park, MD Best practices for phaco device settings by Kenneth L. Cohen, MD Using a phaco flow pump to your advantage Phaco fundamentals: Device settings and best practices for routine to complex phacoemulsification Power modulations for phacoemulsification with a simultaneous side-to-side motion resulting in an elliptical motion to increase the efficiency of breaking up the lens. With torsional ultrasound, the phaco tip is angled and moves in a circular oscillating motion that also aims to maximize cutting efficiency. Both technologies decrease heat production and can result in clearer corneas postop. Pulse and burst modes Traditional phaco is continuous, which means exactly what the name implies—energy is delivered the entire time the foot pedal is pressed. Pulse mode is a power modulation that allows for automated alternat- ing of phaco-on and phaco-off time. The term "duty cycle" refers to the ratio of phaco-on time to total phaco-on and phaco-off time, ex- pressed as a percentage. The concept to understand is that the number of pulses per second is independent of the duty cycle. Traditional pulse has a duty cycle of 50%, so that 500 ms of ultrasound energy is delivered per second, which cuts down to 50% of energy delivered compared to the continuous mode. The number of pulses is set to the surgeon's preference. Burst mode is a power modu- lation in which the time interval between each burst is dependent on depression of the foot pedal. The farther the foot pedal is pressed, the shorter the phaco-off time becomes, and maximum foot pedal depression is equivalent to continuous phaco. Hyperpulse and hyperburst extend the range of programmable settings. Traditional pulse mode is Kenneth L. Cohen, MD F low with a peristaltic pump refers to how fast that wheel is turning, which in turn indicates how fast fluid is moving through the device. If you occlude the tip, the pump still turns. No fluid can enter, so the vacuum in the line starts building. Eventually you will hit a limit, and that's when the pump stops turning. One question many people ask is if you do not have an occluded tip, do you get vacuum? Although there will never be a maximum vacuum in this situation, you will still get some vacuum. You will see the vacuum go up by increasing the ramp speed, and your tip is a point of resistance. Although many cataract surgeons like peristaltic pumps, there is the concern that you will have uncon- trolled vacuum pulling things for- ward. If this occurs, the flow is too high. You have to lower your flow rate or lower your vacuum. I tend to think of flow and vacuum as working independently of each other, but they also work together. Think of flow as speed. The faster that pump turns, the faster fluid has to go through. If the pro- cedure seems to be taking too long, maybe you need to turn up the flow. If surgery is going too fast, lower the flow rate so you in turn lower the speed. Think of vacuum as akin to grip. If things keep falling off, you need to increase your grip. Flow has a lot to do with distal followability. With epinucleus removal, it's the flow continued on page 67

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