Several variables affect post-occlusion surge

Key Points

"This a great deal that had to be evaluated before we could compare what happens in post-occlusion surge in a model in which we compared instruments," he said. "We had to determine the actual vacuum, and there are substantial differences among commercially available machines compared with the manufacturers' claims." Dr. Olson noted that he and colleagues published related research in the Journal of Cataract and Refractive Surgery (2006;32:1374-1377).

"We also had to determine actual flow and also found substantial-even clinically relevant-differences from what the manufacturers claimed," he said. "We also had to determine vacuum at different flow parameters. Finally, we had to correct these parameters to determine what happens during post-occlusion surge." Dr. Olson added that he and colleagues published related research in the AJO (2006;142:387-392).

Dr. Olson and co-author Dan Georgescu, MD, PhD, from the same institutions, studied four phaco systems (Legacy, Alcon Laboratories; Infiniti, Alcon Laboratories; Millennium venturi and peristaltic, Bausch & Lomb; Sovereign with WhiteStar, Advanced Medical Optics).

Prior to the start of their research, the investigators evaluated various parameters in the phaco systems to normalize flow and vacuum among the machines.

"Regarding vacuum, we found that with 20-and 19-gauge tips, there was no difference. There was a spread in vacuum among the different instruments. The flow was the percent indicated with the 20-gauge tip," he said. "Most of the phaco machines were fairly consistent, but the Millennium peristaltic was 17% below what was expected, which was highly statistically significant. The standard deviation was very small, making this appear to be a problem with calibration but nevertheless something that has to be corrected to obtain a true comparison of post-occlusion surge."

Drs. Olson and Georgescu used eye-bank eyes, from which they removed the irises to avoid blockage of the tips before the various phaco instruments were inserted. Occlusion was simulated by blocking and releasing the outflow line to evaluate how the various machines performed. The anterior chamber depth was monitored continuously on a video monitor, Dr. Olson said.

By creating a model using 430 mm Hg vacuum, a reliably high vacuum level that was created for all the phaco machines (75-cm bottle height, 24 ml/min flow, and a 20-gauge tip), the machines varied quite substantially. All of the differences reached statistical significance.

The Millennium system had the least surge, followed by the Sovereign, Infinity, and Legacy systems, the latter of which was a significant outlier, according to Dr. Olson. No aspiration system (Aspiration Bypass System, Alcon Laboratories) tip was used.

The data were as follows: Millennium venturi (only vacuum controlled), >2 mm; Millennium peristaltic, 0.047 ± 0.018 mm; Sovereign, 0.110 ± 0.028 mm; Infiniti, 0.153 ± 0.034 mm; and Legacy, 0.317 ± 0.064 mm (p < 0.01 for all machines).

The aspiration tip, which has a port that always allows flow, even in the presence of occlusion, substantially changed the vacuum level.