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Power-matrix pulsed ultrasound reduces total energy and time in phaco chop
Study contrasts pulsed with continuous ultrasound phacoemulsification.
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BOSTON — Use of power-matrix pulsed phacoemulsification reduces the total energy and time to remove the nucleus, according to a study that compared pulsed ultrasound with continuous ultrasound using the Allergan Sovereign system.
“The Sovereign employs a computer-controlled, sophisticated pulsing of the phaco power that reduces the total energy needed by 50% in a 3+ nuclear density compared to conventional continuous delivery of phaco power,” said investigator Roger F. Steinert, MD, an assistant clinical professor at Harvard Medical School and in group private practice here.
The prospective study consisted of a total of 76 eyes: 52 eyes with 2+ nuclear density and 24 eyes with 3+ nuclear density. Nuclear hardness was based on the patient’s preoperative assessment using the Lens Opacity Classification System and age. “Those two factors together are fairly good predictors of the behavior of the nucleus intraoperatively,” Dr. Steinert said. Consecutive patients were randomized between continuous surgeon-controlled phaco and pulsed phaco.
Seven options
The Sovereign system has seven power-matrix options. However, “out of practicality, I chose only two options,” Dr. Steinert said. “I picked the two options that seemed the most different, so that I could sort of push the limit.” Of the eyes assigned to pulsed phaco, the 2+ nuclei underwent high power, and the 3+ nuclei underwent low power.
The standard Nagahara horizontal phaco chop, along with high vacuum, was the surgical technique for all eyes. “For the 2+ nuclei, the maximum vacuum was 200 mm Hg, and for the 3+ nuclei, the maximum vacuum was 300 mm Hg,” Dr. Steinert said. However, in all cases, a 0°, 20-ga needle was employed.
For total foot pedal time, there was no difference between the continuous group and the high-power pulsed group for level 2 nuclear density. The same held true for level 3 nuclear density. “Although we’re spending more time in position three of the foot pedal (more frequent, shorter pulses) because it is a harder nucleus, there is absolutely no difference — not clinically and not statistically — between continuous and low pulse,” Dr. Steinert said. In essence “we’re not getting out of the operating room any faster, at least with my technique, in these two particular choices of power matrix.”
Effective time difference
However, for equivalent phacoemulsification time, there was a difference. “For the 3+ nuclei, there is a considerable difference between continuous and low-power pulse,” Dr. Steinert said. “Low-power pulse cuts down the amount of time and energy as integrated with the equivalent phaco time calculation.”
Dr. Steinert said that, in retrospect, “it was completely obvious” why there was “absolutely no difference” in the 2+ nuclei. “The best we can say about that particular choice is it served as a control,” he said. After all, “high-power pulse is continuous for the first 50% of pedal travel. Because these were relatively softer nuclei, we rarely went beyond the first 50%. Most of these cases were, in fact, done in continuous mode because they were softer nuclei.” If a surgeon desires to find a difference, he or she needs to “go back and try a low-power pulse with the +2 nucleus group,” Dr. Steinert said.
Average power was an advantage of low-power pulse. “The moderately hard nuclei had almost half the amount of average power used,” Dr. Steinert said. “Interestingly, this was identical to the power used on the continuous or high power pulse for the 2+ nuclei.” There were also no detectable differences in day 1 outcomes between the pulsed and the continuous ultrasound using standard clinical measures. “Endothelial cell loss and visual acuity recovery appear similar,” Dr. Steinert said.
Selecting a pulse
Overall, for the 2+ nuclei, “we achieved equivalent results with continuous and high-power pulse phaco,” Dr. Steinert said. “This points to the fact that you need to select a pulse or burst system that matches the density of nucleus and makes sense for it. So, that was an expected result.” On the other hand, for the 3+ nuclei, “the low-power pulse significantly reduced the total amount of ultrasound energy necessary to perform the surgery. It was statistically significant, but I think clinically significant as well.”
Dr. Steinert said he believed this is a preliminary study. “What it really did for me was validate the methodology,” he said. “We now have the tools. What we lack is the mental discipline to objectively assess our surgical techniques. We can use this powerful tool of randomization to help with that.” Dr. Steinert intends to conduct further studies on different strategies of power modulation in phaco surgery “to achieve the goal of absolutely minimizing the delivery of energy inside the eye in order to obtain an equal, or hopefully even better, clinical result.”
For Your Information:
- Roger F. Steinert, MD, can be reached at Ophthalmic Consultants of Boston, 50 Staniford St., Ste. 600, Boston, MA 02114; (781) 487-2200; fax: (781) 487-5717; e-mail: rfsteinert@eyeboston.com. Ocular Surgery News could not confirm whether or not Dr. Steinert has any financial interest in the Sovereign system.