WhiteStar power upgrade reduces phaco energy by up to 40% after eight-month ‘learning curve’

Stefanie Petrou-Binder MD in Ludwigshafen, Germany

EVEN for the experienced surgeon, a new system brings a new learning curve.
A study of AMO’s Sovereign phaco system with the WhiteStar power upgrade conducted at Heidelberg University, Germany showed a remarkable reduction in phaco time and power as surgeons gained familiarity with the system.

Distribution of nucleus density.	Distribution of phaco power with time.

“Using the Sovereign phaco system with Whitestar power modulation technology for eight months revealed a definite learning curve and proved that the system generates less heat, uses less phaco energy and lowers the effective phaco time,” reported Gerd Auffarth MD at the annual congress of the German-Speaking Association for Intraocular Lens Implantation and Refractive Surgery (DGII).

In a study which included 219 cataract patients, Dr Auffarth performed cataract surgeries using WhiteStar technology (AMO) for eight almost consecutive months. He made clear-corneal cuts and used topical anaesthesia (Xylonest gel).

He worked with two phaco settings for sculpting (Phaco 1) and quadrant removal (Phaco 2). For nucleus sculpting, he implemented the phaco mode of the Sovereign system with 60% power, occlusion mode off, maximal vacuum of 150mmHg and ASP 26cc/ml (Phaco 1).

For quadrant removal Dr Auffarth then used 25/35% power, occlusion mode on, maximal vacuum 300/175mmHg and ASP 30/28cc/ml (Phaco 2).
In addition, he evaluated the temperature changes of the eye in six patients with infrared thermotopography, a method which is very sensitive to even subtle temperature changes, on and in the eye. He compared the heat generated through pulsed phaco (WhiteStar) to heat generated through non-pulsed phaco for the same lens densities.

Other operative measures included the effective phaco time (EPT), percentage phaco power and lens density (scale from zero to five). Lens density among patients in the protocol ranged between 1+ and 5+.

The investigators correlated the relationship between the lens density and the percentage of ultrasound energy required for emulsification. They also correlated lens density with EPT. The investigators calculated and compared these parameters for each month of the investigation. Dr Auffarth reported that the mean EPT calculated in the first month of surgery using the Sovereign system with WhiteStar technology was 8.13±7.5s. The mean phaco energy in the first month was 12.5±3.8%.

After four months of experience with the Sovereign, the mean EPT dropped to 4.9±4.0s. The mean phaco energy was 8.8±3.9% after four months. These values remained stable for the remainder of the investigation.

Further analysis showed a positive correlation between lens density and ultrasound power as well as between lens density and EPT.
Infrared topography revealed that non-pulsing phaco on denser lenses (Ž3) created local temperature peaks of up to 40-48°C. Temperatures in excess of 45°C may cause wound burning, which is characterised by whiteness and contractions at the wound, and may eventually lead to astigmatism.

The researchers reported that the same lens densities could be emulsified using the micro-pulses of the Whitestar technology, with temperatures not exceeding 24-26°C.
Dr Auffarth explained that two of the problems with standard phaco are the heat it generates through the movement of the phaco tip and the “chatter” of the lens fragments caused by the cavitation energy. Chatter involves the bouncing back and forth of lens fragments in front of the phaco tip, which may both prolong phaco time and damage endothelial cells.

With WhiteStar, the rapid train of on/off pulses (burst/rest) allows cavitation energy to build up and break down the lens, while affording the ocular tissues a brief resting phase during which heat can dissipate. Along with cooling, the rest phase also permits the reacquisition of lens fragments by the phaco tip.

As it is possible to vary the length of the micro-pulses with Whitestar, Dr Auffarth explained that the surgeon can determine a suitable working mode with this technology for different phases of surgery.

For example, the total burst time (ultrasound energy on) per second may be set at 700ms ultrasound per second with 300ms rest per cycle. The same cycle can be attained with different burst/rest combinations, such as with ten 70ms bursts and ten 30ms rest periods, without losing efficacy.

“Once we learned how to use the WhiteStar system to its full advantage, we could sculpt the lens with 30% less phaco power. Energy reduction minimises trauma. We were able to implement the divide-and-conquer-technique (chop technique) with up to 40% energy reduction,” Dr Auffarth said.

While other surgeons who have used Whitestar agree to the multiple benefits of this new technology, not all have noted a similar learning curve.

In a report on the use of WhiteStar with a bimanual technique, RJ Olsen MD of the Moran Eye Centre, Utah, US said that WhiteStar showed no significant learning curve, but afforded him a dramatic decrease in ultrasound time, although he performed the procedure the same way he did before. He also reported an average phaco time of less than one second.

Dr Auffarth commented that each surgeon approaches a new system or technique with a modicum of caution and with varying degrees of initial success. A learning curve can be expected, particularly for a system which allows the surgeon to individually modulate settings to facilitate different stages of surgery.

Gerd Auffarth MD, PhD
University of Heidelberg, Germany
Email: ga@uni-hd.de