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Ultrasound energy in phaco severely diminishes endothelial cell density
J Cataract Refract Surg. 2009;35(4):732-737.
Vacuum levels during phacoemulsification significantly influenced endothelial cell loss, but total infused fluid did not seem to affect endothelial cell density.
“Based on our results, to have a safe and effective procedure, we suggest low hydrodynamic parameters (flow rate and vacuum) for surgeons with low experience, especially residents in training, and high hydrodynamic parameters for surgeons with more experience to reduce the time of surgery,” the study authors said.
The prospective, randomized clinical trial included 30 patients who underwent phaco with high vacuum and 30 patients who had phaco with low vacuum. All procedures were performed with the Sovereign WhiteStar phaco platform (Abbott Medical Optics) using the stop-and-chop technique.
Mean ultrasound power was 9.2% in the low vacuum group and 13.1% in the high vacuum group. Total ultrasound energy and fluid consumption were similar in both groups. Endothelial cell density was assessed preoperatively and 1, 6 and 12 weeks after surgery.
Study data showed mean endothelial cell loss of 9% in the low vacuum group and 9.6% in the high vacuum group 12 weeks after surgery. Ultrasound energy had a statistically significant correlation with endothelial cell loss (P < .001), results showed.
The authors have looked at endothelial cell loss after phacoemulsification with a new twist. Rather than look at a correlation with technique, machine or ultrasound power, they decided to look at high flow and vacuum vs. low flow and vacuum while trying to control for all other parameters. The toughest parameter to control is nuclear density, as it is well-documented that endothelial loss correlates with nuclear density, although aggressive reliance on mechanical segmentation can go a long ways in minimizing this correlation. It is not clear how well the authors controlled for nuclear density. However, their randomization should go a long way in minimizing this problem.
What they found is the amount of fluid used and the effective phaco time were statistically similar for the two procedures, even though the flow was much higher in one group. How could this be? The total phaco time was significantly less in the high flow group while the power was up, hence the equivalent effective phaco time. Endothelial cell loss was the same in both groups.
When we looked at ultrasound and irrigation damage to fresh human eye bank eyes over 20 years ago, we found essentially no damage due to either irrigation or ultrasound in the anterior chamber. We could only document damage when bubbles were in the system and bounced off the phaco tip. So we surmised that the amount of nuclear debris bouncing around was the real culprit, and that hypothesis fits perfectly with this paper. As long as effective phaco time is similar and the technique is similar, the endothelial damage will be similar. So the take-home message is: Use ultrasound sparingly on nuclear fragments and the cornea will love you.
– Randall J. Olson, MD
OSN Cataract
Surgery Board Member