San Francisco-A comparison of wavefront-guided andwavefront-optimized treatments performed using the WaveLightAllegretto laser (WaveLight Laser Technologie AG) and the IntraLasefemtosecond laser system (IntraLase Corp.) indicates excellentrefractive predictability and visual outcomes can be obtained usingboth treatments, Karl G. Stonecipher, MD, reported at the annualmeeting of the American Society of Cataract and Refractive Surgery.
"With earlier lasers," he pointed out, "the importance of asphericity in the ablation contour was not considered, which led to the induction of high amounts of spherical aberration. Some of the early outcomes led us to believe that we could do something better to reduce some of the spherocylinder errors and not change some of the higher-order aberrations that were being measured." Dr. Stonecipher cited the work of Professor Theo Seiler, and Dr. Michael Mrochen in this area.
Differences of procedures
Dr. Stonecipher, who is in private practice in Greensboro, NC, reported the uncorrected visual acuity (UCVA) and the preoperative versus the postoperative UCVA after treatment with either a wavefront-optimized or wavefront-guided procedure. These 3-month data were taken from the FDA study that included 332 eyes with up to 7 D spherical equivalent and 3 D of cylinder.
"The preoperative best spectacle-corrected visual acuity (BSCVA) compared with the postoperative UCVA are probably some of the best data we have seen in an FDA trial," he commented. In both groups, 93% of eyes had an UCVA of 20/20; 76% and 64%, respectively, had an UCVA of 20/16; and 22% and 25% had an UCVA of 20/12.5. The postoperative UCVA was better than the preoperative BSCVA in 89% and 86% of eyes, respectively.
Dr. Stonecipher pointed out that a comparison at the 20/16 level favored the wavefront-optimized group because there was a great deal of previous experience with the platform and many of the investigators who participated in the study had fine-tuned nomograms from the original FDA trials for approval of the wavefront-optimized platform.
The key points that he emphasized are that most eyes have low preoperative aberrations. Eyes with very low aberrations had similar results in both groups. The effectiveness of wavefront-guided LASIK depends on the preoperative higher-order aberration levels and the spherocylinder treatment amount.
"In this study population, 83% of eyes had a root mean square of higher-order aberrations (RMSH) of 0.3 μm or less; 93% of the patients had an RMSH of 0.4 μm or less. Eyes with low preoperative aberrations have similar results with wavefront-guided and wavefront-optimized procedures," he said. With the lower-order RMSH, the two procedures were equivalent, he pointed out. However, when the RMSH reached 0.3 to 0.4 μm, the wavefront-guided procedure begins to be favored and the differences reach statistical significance, according to Dr. Stonecipher.
The second important factor is the amount of spherocylinder treatment. The study indicated that at the 0.2-μm level the two procedures are equal. At 0.3 and 0.4 μm, the situation begins to change; at this point, patients with 0 to 4 D of spheroequivalent start to show improvement. In terms of visual outcomes this is seen at the 20/12.5 level. Above 0.4 μm the wavefront-guided procedure is better.