Mechanisms and Safety of Ultrasound Phacoemulsification

ObjectiveA comprehensive technical and biomedical analysis of ultrasound-induced effects during phacoemulsification cataract surgery (PCS) and an assessment of the potential risks associated with ultrasound emulsification MethodsModeling ultrasound wave propagation and intensities using the finite element method (FEM). Cavitation onset was experimentally validated in a pressure chamber observed with a high-speed camera. The thermal effects of ultrasound energy were estimated through established physical and thermal models and confirmed in a cuvette setup using thermistor probes. ResultsAt the distal end of the PCS tip, the ultrasound wave intensity reached 0.2 W/mm2, resulting in ocular tissue displacements in the anterior chamber below 2 {micro}m. The temperature rise in the anterior chamber was less than 0.2 {degrees}C/s. Both observations indicate negligible mechanical and thermal risk to ocular tissues. High-speed imaging confirmed cavitation confined to the tip region. Emulsification efficacy was maintained even under conditions that suppressed cavitation, including elevated ambient pressures and cavitation-inhibiting fluids. Results indicate that mechanical fragmentation by tip oscillation ("jackhammer effect") is the only relevant emulsification mechanism, while cavitation plays a negligible role. Acoustic streaming was observed during ultrasound excitation without phaco sleeve. During phacoemulsification, the sleeve suppressed acoustic streaming into the anterior chamber. ConclusionsThe findings validate the safety of ultrasound-based PCS and confirm that tissue fragmentation is primarily driven by the oscillating tips direct action.