Qualitative and quantitative analyses of stroke dynamics and microfluidics of phacoemulsification probes operating in different modes.

PURPOSE: To compare phacoemulsification (phaco) tip movement, microfluidic dynamics, and tip-to-load interaction between longitudinal, torsional, and elliptical ultrasound (US) modalities.

SETTING: Phacodynamics Laboratory, Clínica Oftalmológica, Pasteur, Santiago, Chile.

DESIGN: Experimental study.

METHODS: All experiments were performed using a fluid-filled optical test chamber and phaco tips that were US power activated. Tip movement was evaluated using stroke tracing and stroboscopy imaging techniques. Qualitative and quantitative assessments of microfluidic behavior were performed using bead seeding and high-speed shadowgraphy imaging combined with particle-image velocimetry and vector analysis. Material load interaction was measured using a rubber sphere that represented lens material.

RESULTS: Longitudinal and torsional US tips showed precise forward-and-backward and side-to-side (lateral) movement, respectively. Elliptical US tips scribed a 2-dimensional ellipsoid path that slightly changed in shape and orientation plane at higher powers. Longitudinal and lateral components of tip motion were evident in elliptical mode. Regular fluid flow was observed with longitudinal mode (forward-directed flow away from the aspiration port) and torsional mode (steady backflow into the aspiration port). In elliptical mode, bead repulsion, erratic bursts of acoustic streaming, oblique backflow, and areas of multidirectional flow were observed. The longitudinal mode caused the material load to bounce against the tip, whereas the torsional mode maintained a consistent load attraction. In elliptical mode, the material load rotated slightly and bounced away from the tip in irregular intervals when attraction was achieved.

CONCLUSIONS: Tip movement, microfluidic behavior, and material load interaction were related within but varied across US modalities. The elliptical mode showed a movement pattern with longitudinal and lateral components and irregular microfluidic behaviors.

FINANCIAL DISCLOSURE: Dr. Zacharias received research funding from Alcon Laboratories, Inc. He has no financial or proprietary interest in any material or method mentioned.