Favorably low enhancement rates found using wavefront-optimized excimer laser platform

October 15, 2008

A retrospective analysis has found favorably low enhancement rates using a wavefront-optimized excimer laser platform (WaveLight Allegretto Wave, Alcon).

Key Points

Atlanta-Results of a retrospective analysis indicate that a low rate of enhancement procedures exists among eyes that undergo wavefront-optimized LASIK or advanced surface ablation (ASA) using a proprietary excimer laser (WaveLight Allegretto Wave, Alcon Laboratories), according to researchers from the Emory Eye Center, Emory University School of Medicine Department of Ophthalmology in Atlanta.

"Both LASIK and ASA are considered highly efficacious refractive surgery procedures. However, available data indicate that between 5% and 15% of eyes treated with various platforms require some type of enhancement to optimize the uncorrected visual acuity [UCVA] outcome," said Alfred A. White Jr., a medical student at Emory University.

"Our experience with use of the [proprietary excimer laser] platform compares favorably with these reports," he said. "Minimizing the rate of enhancements is important because these re-treatment procedures are accompanied by risks. These [risks] include epithelial ingrowth and flap-related complications with LASIK and corneal haze formation following ASA procedures."

The review included all patients at that institution who underwent ASA or LASIK using the excimer laser during 2005. All procedures were performed by a single surgeon, J. Bradley Randleman, MD, an associate professor of ophthalmology at Emory.

Eyes were excluded from the study if preoperative or postoperative data were incomplete for them. The review was based on data from 855 eyes of an approximately equal number of men and women. Approximately three-fourths of the eyes underwent LASIK, and the rest were treated with ASA. The vast majority of procedures (>91%) were treatments for myopia. The patients had a mean age of 37.6 years (range, 18 to 70 years). Their mean preoperative manifest refraction spherical equivalent (MRSE) was –3.58 D (range, +5.00 to –9.63 D), and mean astigmatism was +0.60 D (range, 0 to +5.00 D).

UCVA outcomes demonstrated that the initial treatment was very successful. Postoperative UCVA was 20/20 or better in 72% of eyes, and UCVA of 20/40 or better was achieved in 99.5% of eyes. Only 55 eyes (6.2%) underwent an enhancement procedure. LASIK accounted for about three-fourths of the enhancement cases; ASA accounted for the rest.

Multiple variables compared

The group of eyes that underwent enhancement was compared with the group that had no re-treatment with respect to multiple variables including age, preoperative MRSE, astigmatism, corneal thickness, keratometry, room humidity, room temperature, and flap thickness. Astigmatism was the only feature that was significantly different between the two groups, with the eyes undergoing enhancement having a significantly higher mean preoperative astigmatism than the eyes that were not re-treated, 0.87 versus 0.58 D, respectively.

Season of surgery had no significant association with enhancement rates. The enhancement rate was highest in the summer (7.8%), followed by the spring (6.4%), and it was similar in the winter and fall (5.7%).

Further analyses comparing specific preoperative refractive characteristics were conducted excluding season as a factor. The results showed that eyes with hyperopia or more than 1 D of astigmatism had significantly higher re-treatment rates than myopic eyes or those with less preoperative astigmatism.

The rate of enhancement among hyperopic eyes was 12.8% compared with 6% among myopic eyes, whereas eyes with astigmatism >1 D had a 9.1% rate of enhancement compared with a 5.3% rate among eyes with less astigmatism. The rate of enhancement was about three-fold higher comparing eyes with >2 D of astigmatism against the reference group with less astigmatism, 16.4% versus 5.5%.

Patient gender and procedure type (ASA versus LASIK) were not significantly predictive of a risk of enhancement.

"Notably, most eyes [72.2%] undergoing enhancement in this study had UCVA better than 20/40 prior to enhancement," Dr. Randleman concluded.