Longitudinal, torsional ultrasound
Traditional cataract removal by longitudinal ultrasound uses a forward-and-backward tip motion to produce the physical interaction required for phacoemulsification, Dr. Zaugg noted.
Longitudinal ultrasound is less than optimally efficient because the lens particle can bounce off the tip during the forward motion, the effect commonly called chatter. The backward motion of the tip also creates a transient void during which no energy is transferred to the cataract.
Torsional ultrasound oscillates the tip in a side-to-side motion, with the tip subtending an arc. This motion induces a sheering action that is claimed to be more efficient because the tip remains in contact with lens nuclei throughout the arc and produces more constant emulsification. The lack of forward motion is said to result in less chatter, which could also improve efficiency and patient safety.
In what may be the first head-to-head trial of the two tips, researchers fixed porcine lenses in formalin and cut the lenses into 2.0-mm cubes to simulate brunescent human nuclei. These extremely dense nuclei require more effort, more phaco energy, and more time to treat successfully than the typical cataract, Dr. Zaugg noted.
The individual lens cubes were phacoemulsified (Centurion Vision System, Alcon) using a standard 30° Kelman 0.9-mm tip and the OZil Torsional Balanced tip at the same settings: a constant vacuum (500 mm Hg), constant aspiration rate (50 mL/min) and constant IOP (50 mm Hg) at 60% and 100% torsional amplitude. Each torsional setting included longitudinal power settings of 0%, 25%, 50%, 75% and 100%. A total of 20 runs were conducted at each setting.
Efficiency was measured as the time needed for the complete emulsification and removal of each lens cube. Chatter events for each trial were also recorded.