Purpose: To compare the potential for thermal injury to ocular structure resulting from phacoemulsification ultrasound energy and erbium:YAG (Er:YAG) laser output.
Setting: Morse Laser Laboratory, Massachusetts Eye and Ear Infirmary, Harvard Medical School, Boston.
Methods: Ultrasonic phacoemulsification energy and ER:YAG laser output (10 J/cm2, 10 Hz, 0.3 watts) sufficient for lens removal were applied to model systems and human cadaver eyes. Temperatures were measured with ultrafine thermocouples interfaced to a microcomputer data acquisition system.
Results: Although greater than 95% of energy from laser output is converted to thermal energy, temperature rise in model systems and cadaver eyes was 10 to 15 times greater after pulsed application of ultrasound energy than after Er:YAG laser application. At 100% power, approximately 4 watts of ultrasound power is converted to heat. Temperature rise following both laser and ultrasound applications decreased with irrigation in cadaver eyes and increasing volume in a model system. With continuous irrigation (20 cc/min), the temperature rise at 2 minutes measured at the corneal endothelial surface, within the corneal stroma, and in the anterior chamber angle of cadaver eyes was approximately 0.5 degrees Celsius (degrees C) after laser application and 7.0 degrees C after ultrasound application. Without irrigation, temperatures rose 2.5 degrees C after laser application and 35.0 degrees C after ultrasound application.
Conclusion: At operating parameters sufficient for lens removal, the Er:YAG laser imparted less thermal energy to whole eyes and model systems than ultrasonic phacoemulsification.