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In a fluidics test of three phacoemulsification machines, differences were found in vacuum, flow, and postocclusion surge-and these differences were found not only between the three machines but also between the machines' own settings and what they were actually delivering. Other important findings: there is a significant amount of unoccluded vacuum at the tip, and the parameters for what constitutes a safe postocclusion surge can be dramatically different among eyes.
In addition, although the machines' postocclusion surge generally is well controlled, certain eyes might be much more susceptible to damage by it than others.
Dr. Olson and his colleagues compared the fluidics of three phacoemulsification machines: Infiniti (Alcon Laboratories), Signature (Advanced Medical Optics), and Stellaris (Bausch & Lomb).
When set at a flow rate of 60 ml/min, actual flow was 55.8 ±0.4 ml/min for Infiniti, 58.5 ±0.0 ml/min for Signature, and 53.5 ±0.0 ml/min for Stellaris.
Unoccluded flow vacuum at a flow of 60 ml/min was 197.7 ±0.7 mm Hg for Infiniti, 115.1 ±2.3 mm Hg for Signature, and 179.8 ±0.9 mm Hg for Stellaris.
Using a 32-year-old eye-bank eye, with the machines set at 550 mm Hg vacuum, a 60 cm bottle height, and a 45-ml/min flow with 19-gauge tips, Dr. Olson measured postocclusion surge at 0.33 ±0.05 mm for the Infiniti, 0.13 ±0.04 mm for Signature, and 0.16 ±0.06 mm for Stellaris.
In an 81-year-old eye-bank eye, at 400 mm Hg vacuum, 70 cm bottle height, and 40 ml/min flow with 19-gauge tips, postocclusion surge was 1.51 ±0.22 mm for Infiniti, 0.67 ±0.01 mm for Signature, and 0.83 ±0.06 mm for Stellaris.
"We looked specifically at unoccluded flow vacuum in a peristaltic system, to see how much vacuum you really need to create the indicated flow at the tip," Dr. Olson said. "It turns out that at aggressive parameters, the passive flow from the peristaltic pump is not enough. You actually must have vacuum to maintain flow."
The most accurate machine for vacuum was Infiniti, and the most accurate for flow was Signature, he said.
"In terms of surge and unoccluded flow, the rankings are Signature, Stellaris, then Infiniti," Dr. Olson said. "And I think it's important to note that in terms of surge, the Stellaris and Signature were closely matched, and when you're looking at unoccluded flow, the Stellaris and Infiniti were very close."
Dr. Olson said that although the actual vacuum was different from the machine-indicated vacuum and also varied between machines, "I don't think clinically there was much impact to that. All of it is close enough. But we had to know that to look at post-occlusion surge eventually."
In terms of the flow findings, with the machines being set to produce 60 ml/min, the Signature was the closest at 58.5 ml/min, Infiniti was intermediate at a little over 55 ml/min, and the Stellaris was the least at 53.5 ml/min.
"You could be setting the machine where you want to get the work done, and it could actually be providing up to 10% less flow than you're asking. Again, there's some clinical importance there, but it's still relatively minor," Dr. Olson said.