Torsional phaco offers surgeon greater efficiency

San Francisco-Torsional phacoemulsification performed with the new OZil handpiece (Alcon Laboratories) and associated software results in more efficient surgery than conventional longitudinal phaco, said David Allen, MD, at the annual meeting of the American Society of Cataract and Refractive Surgery.

Torsional phaco is a new cataract removal modality available for the Infiniti Vision system (Alcon). In torsional phaco, the phaco needle vibrates at ultrasonic frequency (32 kHz) in a torsional way rather than longitudinally. Torsional movement along the shaft of the needle is translated into lateral movement at the tip that is further amplified by tip angulation. The unique action profile of the tip in torsional phaco results in greater efficiency since it eliminates repulsion of nuclear material and by so doing, improves followability.

However, to demonstrate the efficiency of torsional phaco in an objective way, Dr. Allen performed a single-surgeon, randomized study using the flow of balanced salt solution (BSS) through the eye during nucleus removal as a proxy measure. After calculating the sample size needed to demonstrate a statistically significant difference between groups, 84 patients were randomly assigned to surgery with the longitudinal or torsional technique, and the weight of BSS used from the start to the end of nucleus removal was determined using a precision balance.

"Those who have had the pleasure of using torsional phaco can appreciate its improved efficiency when looking through the operating microscope. In this small study, we have been able to show that benefit in terms of a highly statistically significant reduction in the amount of BSS going through the eye," said Dr. Allen, consultant ophthalmic surgeon, Sunderland Eye Infirmary, Sunderland, England.

Dr. Allen noted that increasing evidence shows that simple mechanical direct action of the phaco tip is what induces lens fragmentation in traditional longitudinal phaco. However, the constant repulsion of nuclear material that occurs with the forward stroke of the phaco tip with that technique introduces an element of inefficiency.

"Longitudinal phaco is really only effective during 50% of the phaco tip action except for some possible contribution of cavitation on the backward stroke, but that is controversial," Dr. Allen said.

It was also previously thought that power modulations using rapid pulses or bursts of ultrasound energy resulted in smoother phaco. However, review of intraoperative videos in slow-motion also refutes that concept.

"When the film is slowed to half-speed, one can see frequent repulsive movement as the nuclear material is bounced away from the phaco tip before fluidics bring it back into contact," Dr. Allen said.

He demonstrated the advantage of torsional phaco by showing an intraoperative video at half-speed from a case performed with that technique.

"The nuclear removal is totally smooth, with the material disappearing into the tip without any small repulsive action," Dr. Allen commented.

Experience with torsional phaco also indicates that because it eliminates repulsion and improves followability, surgery can be completed with less turbulence and a reduced need for second-instrument manipulation in the anterior chamber.

"Therefore, this new modality would be expected to have less potential for causing endothelial damage. Demonstrating that torsional phaco translates into a clinically significant difference will be a focus of my future research," Dr. Allen concluded.