High- and low-frequency phaco energy levels behave differently during surgery

April 5, 2008

A preliminary study that measured high- and low-frequency energy in porcine and human eyes on an oscilloscope showed that the energy levels behave differently in the eye during phacoemulsification, according to William Fishkind, MD.

A preliminary study that measured high- and low-frequency energy in porcine and human eyes onan oscilloscope showed that the energy levels behave differently in the eye duringphacoemulsification, according to William Fishkind, MD.

"The phaco tip generates both low-frequency energy at the manufacturer-selected frequency andhigh-frequency cavitational energy," said Dr. Fishkind, clinical professor of ophthalmology,University of Utah, Salt Lake City. "Each kind of energy interacts differently with cataractfragments and intraocular structures."

During this experiment, Dr. Fishkind and colleagues split the energy with sensors attached to acircuit board and an oscilloscope and the behavior of the energy was analyzed on a video forthe amount of energy used during phacoemulsification, the distance the energy traveled in theeye, and the arrangement of the energy spread. He explained that during phaco there are twokinds of energy-direct mechanical energy (jackhammer) that effectively emulsifies nuclei andacoustically generated energy in two forms, that is, low-frequency handpiece-generated energyand high-frequency cavitational energy. The average energy in millivolts was calculated from aformula that includes factors, such as angulation, and the size of the phaco tip.

Dr. Fishkind reported that during back-sculpting of the nucleus there is more energy beingtransmitted to the eye than when the needle moves forward. Fragment emulsification resulted ina peak of low-frequency energy and a peak of high-frequency energy due to cavitational energy,which was surprising, he said.

When he looked at elliptical configurations, Dr. Fishkind found that much less energy wasgenerated due to the low frequency and the lateral movement of the phaco tip. Low-frequencyenergy radiates out from the phaco tip in all directions and bounces off tissue, and highfrequency energy at the phaco tip with cavitation is focused in a 1- to 2-mm diameter cylinderfrom the phaco tip. With torsional configurations, there was a bow-tie pattern of energy withan as yet undetermined amount of energy.

"Energy damages tissue and disrupts the blood brain barrier because of damage to theendothelial junctions," Dr. Fishkind said. "Acoustic energy causes damage. Low-frequency energycan be minimized by using micropulse energy. Energy can be quantified in milliwatts.Longitudinal configurations may have more radiating energy than elliptical and probablytorsional configurations. High-frequency acoustic energy can be minimized by using anelliptical configuration over a torsional configuration."