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Results from a series of bench studies conducted under strictly controlled conditions consistently indicate that torsional phacoemulsification generates less heat at the incision site than longitudinal phaco.
The research, published in 2009 (J Cataract Refract Surg. 2009;35:1799-1805), involved three experiments in which phaco was performed using a certain platform (Infiniti Vision System with Intrepid Fluidic Management System) and either the torsional handpiece (OZil) equipped with a 45° Kelman mini-flared aspiration bypass system (ABS) phaco tip or the standard longitudinal handpiece fitted with a 30° non-ABS microtip (all Alcon Laboratories).
The tips were inserted into a balanced salt solution-filled silicone test chamber from which weights were suspended on a rubber band to simulate incision compression against the silicone sleeve. Aspiration line clamping was done to mimic tip occlusion and a situation where a risk of incision burn is increased, and serial temperature monitoring at the "incision" (sleeve insertion) site was performed at selected times after power application (0, 10, 30, 60, and 120 seconds) using a thermal camera capturing emitted infrared radiation.
"The results of these experiments indicate torsional phacoemulsification has a significant thermal advantage over longitudinal ultrasound for generating less heat at the incision site," said Dr. Miller, Kolokotrones Professor of Clinical Ophthalmology, and chief, Comprehensive Ophthalmology Division, Jules Stein Eye Institute, David Geffen School of Medicine at UCLA, Los Angeles. "Less heat generation resulting in lower operating temperatures with torsional phacoemulsification means safer surgery."
Friction between the vibrating phaco needle and its silicone sleeve is the primary source of heat generation at the incision site during phaco. Observed differences in heat generation between torsional and longitudinal phaco in the experiments can be explained by differences in movement of the two handpieces, he said.
With torsional phaco, which uses a bent tip and creates oscillatory, side-to-side motion, there is amplification of movement at the tip relative to the movement of the shaft. In contrast, with longitudinal phaco, movement at the tip equals the movement of the needle shaft at the incision site, Dr. Miller said.
"Torsional phaco emulsifies the lens in an elegant and efficient manner that is associated with less movement of the needle shaft within the silicone sleeve compared with longitudinal phaco," he said. "Torsional phaco would be expected to cause less friction and less heat generation at the incision site. That's not to say that a corneal burn cannot be produced using OZil. It can."