Longitudinal versus torsional phaco

May 01, 2014

Several new refractive surgical platforms have been introduced recently and many ophthalmologists are discovering they find the new technologies to be more efficient and produce better results.

"It is more difficult to compare different technologies in a real-world setting," he continued.

Traditional longitudinal phaco used a jackhammer-like in and out motion for phacoemulsification. Bioengineers eventually realized that half the energy used in traditional longitudinal motion is wasted because material is only broken up when the tip moves forward. When the tip moves backward between cuts, it only generates more energy and more heat that can damage the eye.

Bausch + Lomb introduced a more efficient longitudinal platform (Stellaris Vision Enhancement System) which cuts using an elliptical lateral motion. Power modulation and pulse shaping are combined to optimize longitudinal ultrasound energy delivery.

Alcon Laboratories introduced the Infiniti Vision System, which adds torsional technology, called OZiL, to cut lens material using circular oscillations similar to turning a doorknob.

However, the motion of the phaco tip is just one of several variables that can affect procedural complications and outcomes.

Power output is important, Dr Hida noted, because lower energy output generally translates into less collateral damage to the corneal endothelium. Balanced fluidics keep the eye inflated, build and maintain currents that bring cataract fragments to the phaco tip, and help keep the tip cool to prevent thermal injury to the eye.

Fluidics are affected by vacuum, which is a function of the type of pump used and tubing size. Microincisions require micro tubing, but micro tubing requires more vacuum, which creates difficulties in managing fluidics.

Both platforms produced similarly good clinical results, but the Infiniti platform showed lower fluid use and shorter operative times, particularly for patients with hard cataracts.

"I use both machines on a regular basis, so there was no learning curve to affect the results of this comparison," Dr Hida said. "Four hundred consecutive and routine cataract patients were prospectively (randomly assigned) to either the Stellaris or the Infiniti platform. Our goal was to compare the clinical and the intraoperative parameters using the same bevel-down technique with both instruments in a real-world population of real patients."

Investigating further

The Stellaris system uses longitudinal ultrasound, a venturi pump, pulsed energy modulation energy via a straight microtip with a 150-µm stroke and a 1.8- to 2.4-mm incision. The Infiniti system uses torsional ultrasound, a peristaltic pump, pulsed energy modulation via a Kelman microtip with a 100-µm stroke and a 2.2- to 2.4-mm incision. The same technique was used for all eyes, including the same ultrasound pulse rate and fluidic settings.

There were no statistically significant differences in patient age or in nuclear density by either LOCS III or Pentacam PNS assessment.

The Stellaris used significantly less total ultrasound time compared with the Infiniti, Dr Hida found, but the total case time was significantly shorter with the Infiniti system. Infiniti also showed significantly less fluid use per patient.

"Both machines are very good," Dr Hida said. "It is not just this study that shows these platforms are an improvement over older technologies. In terms of clinical results, you can use either machine and produce very good results. For patients, visual recovery after surgery is what is important and both machines did very well."

Dr Hida added that he is equally comfortable using either the Stellaris or Infiniti platforms.

He explained that some surgeons have preferences for one technology over another based on differences in their own experience and technique, but clinical outcomes are similarly high regardless of which instrument is used.

From a workflow perspective, Infiniti offers improved case time, which can boost patient throughput, and reduced fluid use, which might have an economic impact, Dr Hida explained.

"Some of my colleagues like one machine over another and some don't care," he said. "What we all agree on is that new technology is changing clinical outcomes for the better."

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