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.