Torsional phacoemulsification may be more efficient than standard phaco. In an experiment in which beads were aspirated or rejected inside a cell serving as an anterior chamber, longitudinal ultrasound phaco was less than 50% aspiration efficient as demonstrated by bead rejection from the phaco tip, whereas torsional phaco had nearly the aspiration efficiency of irrigation/aspiration alone.
For the experiment, beads were injected into an irrigation solution and tracked to identify those that were aspirated or rejected inside a rigid test model serving as an anterior chamber. Longitudinal ultrasound phaco was less than 50% efficient as demonstrated by bead rejection from the phaco tip, whereas torsional phaco had nearly the aspiration efficiency of irrigation-aspiration (I/A) alone, said Ramon Dimalanta, PhD, an engineer at Alcon Research, Irvine, CA.
Dr. Dimalanta conducted the study to compare the aspiration efficiency of torsional and traditional phaco by quantifying the behavior of fluid dynamics that allowed comparison of different phaco modalities.
"With 100% power setting for longitudinal phacoemulsification, the forward and backward movement of the tip causes turbulence, and multiple bead rejection could be seen. With 100% amplitude setting for torsional phacoemulsification, the level of turbulence and rejection of beads are noticeably reduced and its behavior falls between the two previously described," Dr. Dimalanta said.
"Qualitatively, what was observed is that at 0% power the beads simply follow the flow lines. With the addition of longitudinal ultrasound, the beads can be seen qualitatively being rejected away from the phaco tip's opening," he said. "With torsional phaco, there also is bead rejection but to the sides as the bent tip sweeps left and right."
To quantify this activity, Dr. Dimalanta developed an equation to measure aspiration efficiency. "There is a percentage of beads that will be aspirated when phaco modes are energized, which can be compared with the condition in which no energy has been introduced. By definition, [I/A] with no power is 100% aspiration efficient, and any kind of rejection due to ultrasonic energy reduces that efficiency," he explained.
Dr. Dimalanta said that efficiency can be quantified using the "circle of interest," which is defined as three times the diameter of the lumen. Any bead that enters that circle is considered a potentially aspirated bead. It follows, therefore, that any bead that leaves the circle or is rejected has not been aspirated.
In his frame-by-frame analysis of high-speed video images acquired at 600 frames per second, Dr. Dimalanta counted every bead that entered the circle and determined whether that bead was rejected from the circle or was aspirated into the lumen. He used the product of this experiment, 979 images per video acquired in 1.6 seconds each, as a data set for each of the three modalities (longitudinal, torsional, and 0% power-I/A only). The percentage of beads that were rejected or aspirated for each modality was then compared with I/A only to determine aspiration efficiency.
"When phaco power was added, there was an immediate increase in the number of beads in the circle of interest. When looking at the aspiration efficiency, it was easy to see that [I/A] only compared with torsional phaco are almost the same," he said. "The total number of beads aspirated for both phaco modalities was about the same; however, when looking at the number of beads that entered the circle and therefore were potentially aspirable, the efficiency of longitudinal phaco was less than half that of torsional phaco." (Figure 1).
He concluded: "The quantitative conclusion reached at the end of this experiment supports what has been observed qualitatively. That is, the cutting movement or stroke of longitudinal phaco repels material and, in addition, creates turbulence in front of the phaco tip, as demonstrated by the high bead exchange within the circle of interest. With torsional phaco, because the beads are rejected radially away from the center, the bulk of the beads can still easily get into the lumen."