Phacoemulsification fluidics characterized by new lab methods

Implementation of novel techniques to analyze the fluidic signature of phacoemulsification performed using different ultrasound modalities and phaco tips is providing important insights that will be helpful for improving the efficiency and safety of lens removal surgery, said Jaime Zacharias, MD, at the annual meeting of the American Society of Cataract and Refractive Surgery.

Dr Zacharias, of the Pasteur Ophthalmic Clinic in Santiago, Chile, investigated the fluidic environment in a closed system using a 45° mini-flared Kelman-style tip with longitudinal and torsional ultrasound. All procedures were performed using a proprietary cataract lens-removal system (Infiniti Vision System, Alcon Laboratories). Torsional ultrasound was performed with a proprietary handpiece (OZil, Alcon Laboratories).

The results showed that, with longitudinal ultrasound, repulsion of fluid occurred straight in front of and away from the phaco tip. Using 100% phaco power, the fluid stream was moving at a speed of 450 mm/sec, Dr Zacharias said.

With torsional ultrasound and with the tip maintained level in the focal plane, fluid streaming appeared above 85% power in a posterior and lateral direction. Deviating the tip slightly above or below the focal plane while using torsional ultrasound showed almost no ultrasonic streaming effect.

"These findings indicate that torsional ultrasound produces a moderate backward-oriented streaming effect at the plane of the tip, while using torsional ultrasound with the Kelman tip perpendicularly oriented toward the posterior pole provides a very still fluidic environment near the corneal endothelium," Dr Zacharias said.

The analyses were performed using a technique called particle image velocimetry, which is based on tracking the displacement of neutrally buoyant, micrometer-sized glass spheres in a bi-dimensional space. A laser line generator is used to illuminate a thin sheet inside a fluid volume. High-speed video photography is used to follow particle displacement.

Special software can be used to analyze pairs of captured images and generate vectors indicating the speed and direction of the particles in the region of interest. Alternatively, particle displacement also can be calculated by single video frame analysis of particle streak length during exposure, Dr Zacharias said.

"We are working to improve our implementation of this analytic methodology, but our current experience indicates that particle imaging is a very valuable technique for understanding phaco fluidics," he said.