Thermal Imaging Comparison of Longitudinal versus Torsional Phacoemulsification in INFINITI Young Keun Han, M.D., Kevin M. Miller, M.D. Department of Ophthalmology, David Geffen School of Medicine at UCLA and the Jules Stein Eye Institute, Los Angeles, California, USA Authors have no financial interest

Introduction   Heat production during phacoemulsification - Friction between vibrating needle and silicone sleeve   Factor leading to thermal damage - Constriction of the silicone sleeve - Occlusion of aspiration - Prolonged phaco time   Complications as a result of thermal damage - Delayed wound healing - Fistula formation - Damage to the corneal stroma and endothelium - Inability to close the incision - Increased surgically induced astigmatism Olson MD, Miller KM JCRS 2005;31(8):1640-7

Introduction  In torsional phacoemulsification, small-angle rotational movement of the shaft is translated into a nearly horizontal stroke at the tip of the needle. Longitudinal phacoemulsification motion of tip’s end = motion of tip’s shaft Torsional phacoemulsification motion of tip’s end > motion of tip’s shaft  For equivalent longitudinal and horizontal strokes at the tip, torsional phacoemulsification should generate less frictional heat at the incision because of reduced movement at that location.  The purpose of this study was to compare heat generated at the incision in longitudinal versus torsional phacoemulsification.

Materials and Methods   A straight 30  non-ABS MicroTip on a INFINITI ultrasound handpiece and a 45  Kelman Mini-Flared ABS tip on a OZil Torsional handpiece (all from Alcon Laboratories, Inc., Fort Worth, Texas) were each capped with a BSS-filled silicone test chambers (volume 0.85 cc).   25.3-gram weights were suspended using elastomer bands from the silicone tube to simulate tight corneal incisions.   The aspiration line was clamped using needle nose pliers to simulate complete occlusion of the tip.

Materials and Methods   The outside of the chamber was imaged using an FLIR model P60 ThermaCAM TM (FLIR Systems Inc., North Billerica, Massachusetts).   Camera calibration was verified by measuring warm and cold water baths using the infrared camera and comparing against a calibrated thermocouple at temperatures across the experimental range.

Materials and Methods   The thermal camera captured still images of the probes before power application (at 0 seconds), and then 10, 30, 60, and 120 seconds after power application. It determined the highest surface temperature inside a circle drawn around the point of contact of the sleeve and elastomer band. These thermal images were obtained with the handpiece operating in longitudinal mode at 100% power.

Materials and Methods   We performed 3 different types of experiments to simulate 3 different types of “equivalent” power applications. - Experiment 1 Same displayed power on all 3 instrument consoles 40, 60, 70, 100% - Experiment 2 Same stroke lengths at the cutting edge 1.55, 2.40, 2.80, 3.45 mils - Experiment 3 - Fairest comparison Same applied energy (energy = frequency X stroke length) Longitudinal: 37 kHz, torsional: 32 kHz 57.0, 89.0, 104, 129 KHz*mils

Materials and Methods   In Experiment 2, we compared heat production under conditions of identical stroke at the distal end of the tip. To measure the stroke, sleeveless phaco tips were placed inside a fluid tank with a viewing window and imaged using a video microscope (Meiji Techno, Japan).   When ultrasound power was applied, the distance of motion was measured using a VIA-150 video image marker-measurement system (Boeckeler, Arizona, USA). → Video clip

Results Experiment 1: Time vs. Temperature comparing torsional (red) and longitudinal (blue) modalities where the similarity is the displayed power on instrument console: 40, 60, 70, and 100%

Results Experiment 2: Time vs. Temperature comparing torsional (red) and longitudinal (blue) modalities where the similarity is the stroke length as measured at the tip’s cutting edge: 1.55, 2.40, 2.80, and 3.45 mils.

Results Experiment 3: Time vs. Temperature comparing torsional (red) and longitudinal (blue) modalities where the similarity is the calculated applied energy (frequency * stroke length): 57.0, 89.0, 104, and 129 kHz*mils.

Conclusion   These three approaches comparing the thermal differences of longitudinal and torsional phacoemulsification all suggest that the torsional mode is preferable. This may be especially beneficial for surgeons who are less experienced, working with harder nuclei, having longer case times, or utilizing elevated power levels.   In summary this 3-pronged study, where temperatures were measured to determine heat generation behavior, found that torsional phacoemulsification produced less heat than longitudinal phacoemulsification in all comparative test approaches.