Proprietary system reduces variability

January 15, 2011

The ability of a proprietary femtosecond laser system to create a perfectly centered, sized, and circular capsulotomy has been shown in a clinical study to translate into the benefit of reduced variability in effective lens position.

Chicago-The ability of a proprietary femtosecond laser system (LenSx, Alcon Laboratories) to create a perfectly centered, sized, and circular capsulotomy has been shown in a clinical study to translate into the benefit of reduced variability in effective lens position (ELP), said Roger F. Steinert, MD, at the annual meeting of the American Academy of Ophthalmology.

"The increased predictability in ELP achieved using this femtosecond laser system for capsulotomy should lead to more predictable visual outcomes," he said. "Investigating that benefit represents the subject for our next clinical trial."

In an initial study of the performance of the femtosecond laser system for anterior capsulotomy, which was conducted in Budapest, Hungary, Dr. Steinert and co-author Zoltan Nagy, MD, showed the new technology offered much higher accuracy than a manual technique for creating a capsulotomy of intended size. The study included 60 eyes in each group. The achieved diameter of the capsulorhexis was within 0.25 mm of intended in all eyes that underwent the femtosecond laser procedure, but in only 10% of eyes in the manual capsulorhexis group.

The study of the effect of capsulotomy method on ELP included 25 eyes in the laser capsulotomy group and 21 that underwent manual capsulorhexis. Intended size was 4.5 mm in both groups. ELP and anterior chamber-to-axial length ratio were determined at 1 month after surgery using data collected with an optical biometer (Lenstar, Haag-Streit).

The results showed mean ELP was not significantly different between the two groups. However, the standard deviation was less in the femtosecond laser group versus in the manual controls both for ELP as well as for the ratio of anterior chamber depth-to-axial length, and the between-group differences were highly statistically significant comparing the standard deviations for both of these endpoints.

Reducing ELP variability

A shift of just 0.5 mm in the Z-axis location of the implanted IOL will leave the patient more hyperopic or more myopic by a full 1 D, Dr. Steinert said.

"Dr. Wolfgang Haigis has made the point that the key to achieving highly accurate IOL power calculation is the ability to predict the ELP correctly for any given patient and IOL," Dr. Steinert said. "However, in the most commonly used IOL power calculation formulas, the ELP is an assumed value from empirical data, and it remains a major source of IOL power errors after cataract refractive surgery.

"Achieving a consistently sized capsulorhexis will ensure that the ELP matches the IOL power formula and help to achieve more predictable refractive outcomes," he concluded.

FYI

Roger F. Steinert, MD
E-mail: steinert@uci.edu

Dr. Steinert is a consultant to Alcon Laboratories/LenSx.