Torsional phaco offers improvement over standard phaco

Dr. Zacharias described an example of conventional phacoemulsification in slow motion using 21% ultrasound energy, vacuum of 144 mm Hg, and aspiration flow rate of 25 ml per minute. With torsional phacoemulsification, the traditional operation can be performed with lateral displacement of the phaco tip, said Dr. Zacharias, an anterior segment surgeon, Clinica Oftalmologica Pasteur, and director, Phacodynamics Laboratory, Santiago, Chile.

The tip oscillates from side to side at about 32,000 times each second. This makes removing the nuclear fragments more efficient because the fragments are not pushed away from the phaco tip and there is less chance of thermal injury.

In this comparison study, the investigators used a series of optical set-ups with nuclear fragments obtained from cataract extractions in humans in their laboratory. The investigators used high-speed video recording, strobe light video recording, and fluid density gradient detection to demonstrate the differences between standard and torsional phacoemulsification.

Cavitation was defined as the presence of expanding and imploding bubbles during cycles of ultrasonic oscillations.

An undesirable effect

"This creates an undesirable effect during phacoemulsification because of free radical formation, loss of efficiency, and induction of turbulence in the eye," Dr. Zacharias explained.

Turbulence, defined as a loss of laminar flow of balanced salt solution (BSS), and also undesirable, causes random displacement of the lens fragments, loss of efficiency, and direct and indirect damage to endothelium, according to Dr. Zacharias.

Finally, repulsion or dislodgement of the lens fragments from the phaco tip by mechanical forces results in loss of occlusion, loss of efficiency, and endothelial damage.

The lateral movement of the phaco tip resulted in impressive results, according to Dr. Zacharias.

Repulsion reduced

"The patterns of turbulence, viewed using a density gradient detection method and frame-by-frame semiquantitative analysis of the video images, showed a noticeable reduction in turbulence for the torsional system," Dr. Zacharias said. "Repulsion during pulsed-mode phaco was reduced to 40% of the total stroke at the start of each pulse.

"This repulsion rate dropped to almost zero using torsional phaco. Analysis of cavitation using high-speed video analysis and strobe light recordings indicated a totally different pattern of cavitation for torsional phaco, that is, movement away from the cutting border," he added.

The laboratory observations of reduced turbulence and repulsion correlated well with surgical observations of improved followability and control, he said.

During surgery, torsion compares advantageously with axial because it is smoother, according to Dr. Zacharias. The cataract material, once aspirated, is held in permanent contact with the tip while it is being emulsified and aspirated, he explained. The typical bouncing of fragments off the tip using standard phaco is almost completely eliminated, he added.

"Occlusion is maintained and, as a consequence, two significant events occur," Dr. Zacharias said. "First, because there is no repulsion, there is less chance of fragments traumatizing the corneal endothelium. Second, having minimum occlusion breaks means less BSS being consumed. It is a known fact that the more BSS that circulates inside the eye, the more endothelial cells are lost. I currently use [torsion] for all my cases, typically continuous [torsion] with power linearly controlled by the surgeon foot pedal."