Calorimetric Method for Measuring Phacoemulsification Energy Delivered During Cataract Surgery.

Purpose: The purpose of this study was to determine the ultrasound (US) energy delivered to the eye during cataract surgery in Joules, a universal System Internacional (SI) unit of energy. This SI energy unit of measurement allows for comparison among various US modalities, phacoemulsification systems and other applications.

Setting: Laboratory.

Design: Experimental laboratory phacoemulsification energy dissipation model.

Methods: A calorimetric method of energy measurement was used, with a US handpiece, tip, and sleeve were held in place by an adaptor into a test chamber holding 0.5 g of water. Thermocouples measured the water temperature rise. The ultrasound power was tested in 10% increments from 10% to 100% with each ultrasound modality.

Results: High repeatability was observed in both the torsional and longitudinal modality, as indicated by a coefficient of variation less than 0.5 for each power level and the low standard deviation magnitude across the tests (0.020 J/s to 0.149 J/s in the torsional modality and 0.036 J/s to 0.150 J/s in the longitudinal modality, depending on ultrasound power levels). Third order polynomials demonstrated strong and non-linear correlations between ultrasound energy and power levels as indicated by high R2 values (>0.99).

Conclusion: A calorimetric ultrasound energy measurement method provides greater insight into the total energy in the eye. Measuring total phacoemulsification energy in Joules allows for a standardized way to compare total energy across variable platforms and to be used as a potentially more clinically relevant proxy for assessing and improving clinical outcomes.