Pulse and Burst Modes
To reduce the total energy delivered into the eye, the surgeon can use an intermittent rather than a continuous mode of phacoemulsification (Fig 8-3). The delivery of phaco power for only a portion of the cycle also reduces repulsion of material by the vibrating tip (ie, reduces chatter) and improves followability. This method of breaking up the delivery of ultrasonic power into smaller packets of pulses and bursts is called phaco power modulation.
Figure 8-2 Illustration demonstrating the relationship between the phaco tip bevel and holding force. r = radius of the tip.
(Illustration courtesy of Mark Miller.)
Pulse-mode phacoemulsification involves setting the number of pulses per second (ie, the number of intervals during which phaco power is turned on) while the foot pedal is in position 3. These intervals alternate with “rest” intervals during which phaco power is off. The phaco power of each pulse increases as the foot pedal is depressed farther in position 3. When the foot pedal is fully depressed in position 3, each pulse will have the preset maximum power.
Burst-mode phacoemulsification involves delivery of preset power (0%–100%) in single bursts that are separated by decreasing intervals as the foot pedal is depressed through position 3. When the foot pedal is fully depressed in position 3, the power is no longer delivered in bursts but is continuous. Burst mode allows the tip of the phaco needle to be buried into the lens, an essential step for chopping techniques.
The ratio of “power on” time to total time is referred to as the duty cycle. The traditional pulse mode has a default duty cycle of 50%, with the phaco energy on and then off for equal periods (50:50). Modern pulse modes allow detailed control of the duty cycle and the number of pulses per second. As mentioned previously, during burst-mode phacoemulsification, foot pedal position 3 allows linear control between minimum and maximum set duty cycles, with the maximum usually being continuous.
Excerpted from BCSC 2020-2021 series: Section 11 - Lens and Cataract. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.