Determining optimal ultrasound off time with micropulse longitudinal phacoemulsification

Purpose To evaluate the optimum off time for the most efficient removal of lens fragments using micropulse ultrasound (US). Setting John A. Moran Eye Center Laboratories, University of Utah, Salt Lake City, Utah, USA. Design Experimental study. Methods Porcine lens nuclei were soaked in formalin for 2 hours and then cut into 2.0 mm cubes using the Signature US machine with a bent 0.9 mm phaco tip with a 30-degree bevel. The on time was 7 milliseconds (ms), and the off time was varied from 2 to 20 ms in 2 ms steps. Phacoemulsification efficiency (time for fragment removal) and chatter (number of times the fragment bounced from the tip) were measured. Results A nonsignificant linear increase in efficiency was observed with 2 to 6 ms of off time ( R 2  = .87, P  = .24). A significant linear decrease in efficiency was observed with 6 to 20 ms ( R 2  = .74, P  = .006). Conclusions With micropulse longitudinal US, 6 to 7 ms of off time was as efficient as shorter off times; longer off times (8 to 20 ms) showed decreased efficiency. Chatter was minimal and statistically similar throughout. To maximize phacoemulsification US efficiency, an off-time setting of 6 ms is recommended. Financial Disclosure No author has a financial or proprietary interest in any material or method mentioned.