Optimum on-time duty cycle for a transversal ultrasound machine

Abstract

Purpose: To evaluate the optimum on-time setting for the most efficient removal of lens fragments using micropulse ultrasound (US) and Ellips FX transversal US in the Whitestar Signature Pro phacoemulsification machine.

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 cut into 2.0 mm cubes. The US machine was used with a bent 0.9 mm phaco tip and a 30-degree bevel. The off time was set to 6 milliseconds (ms) and the on time varied from 4 to 10 ms in 1 ms increments. Efficiency (time for fragment removal) and chatter (number of times the fragment bounced from the tip) were measured.

Results: A linear incremental increase in efficiency was observed between 4 ms and 6 ms. The most statistically significant efficiency was achieved with an on time of 6 ms. On times shorter than 6 ms were significantly less efficient (P = .05). Greater on times (7 to 10 ms) did not result in a significant difference in efficiency (P = .72), but did appear to have more chatter events when comparing on-time settings of 7 to 10 ms with 4 to 6 ms (P = .02).

Conclusions: With micropulse transversal US, 6 ms of on time was as efficient as longer on times. To maximize phacoemulsification efficiency and minimize chatter events, an on time of 6 ms is recommended.