Outcomes excellent with femtosecond, mechanical device

Higher-order aberrations were identical in each group, according to Edward E. Manche, MD, speaking here at the XXIV Congress of the European Society of Cataract and Refractive Surgeons, although a more accurate, reproducible flap thickness was achieved with the femtosecond laser. Differences in uncorrected and best-corrected visual acuity between the femtosecond laser and the microkeratome were observed at early time points but began to diminish by 6 months and had disappeared by 12 months, according to Dr. Manche. He is director of refractive surgery and cornea/external diseases, Stanford Eye Laser Center, and associate professor of ophthalmology, Stanford University School of Medicine, Stanford, CA.

In this study, 100 eyes of 50 subjects were treated on the VISX CustomVue platform; contralateral eyes of each subject were randomly assigned to the femtosecond laser or the microkeratome. A Fourier software upgrade was installed after the first eight subjects were treated. A slight offset was made to the microkeratome prior to the study to obtain best results; no offsets were performed after the software upgrade, and none were made at any time to the femtosecond laser.

The femtosecond laser was programmed using a 15-kHz system with a 110-µm desired depth and a 9.2-mm diameter. A mean flap thickness of 119.1 ± 18.1 µm was achieved. With the microkeratome group, a 160-µm head was used with a 9.5-mm diameter. The mean flap thickness achieved was 137.3 ± 21.2 µm.

No significant complications were seen in either group; three patients had loose epithelium in both eyes, and one eye in the laser group had a narrow hinge.

UCVA results

Results for uncorrected visual acuity (UCVA) indicated that both groups were seeing quite well at 1 month postoperatively. All eyes achieved an UCVA of 20/30 or better.

"What we noticed at the 1-day and 1-week point was that there was a greater percentage of eyes in the femtosecond group that had UCVA of 20/16 or better, and this was statistically significant," Dr. Manche said.

By 6 months, differences between the groups (data available for 12 eyes in each) had tightened. As at 1 month, all eyes had UCVA of 20/30 or better, but although more eyes in the laser group had UCVA of 20/16 or better, the difference was not clinically significant.

At 1 year, outcomes were identical in both groups; 100% of eyes (data available for 35 in each group) had UCVA of 20/25 or better.

Evaluating UCVA 1 month postoperatively versus preoperative best-corrected visual acuity (BCVA), both groups gained lines: 33% (an average of 0.09) for the laser-treated eyes and 16% in the microkeratome-treated eyes (an average of 0.20). This difference was statistically significant (p = 0.03).

"At 6 months, the advantage lessened, but still 26% of the eyes in the [laser] group versus 14% in the [microkeratome] group gained lines," Dr. Manche said. The average change for the laser group was –0.12 lines, and –0.39 lines for the microkeratome group.