Laser combinations weighed for LASIK results

June 15, 2009

No statistically significant differences were found in the results of LASIK performed with two combinations of devices for femtosecond flap creation and excimer laser vision correction. Both systems produced excellent clinical outcomes. One combination (VisuMax and MEL 80, both Carl Zeiss Meditec), however, was associated with less scatter and more predictability for refractive outcomes than another (Allegretto Wave Eye-Q, Alcon Laboratories; IntraLase FS60, Abbott Medical Optics). Additional research is needed to determine what effect the two femtosecond lasers might have had on the results.

Key Points

A LASIK and refractive surgeon in Denver, Dr. Dishler said he routinely uses both laser combinations in his private practice and performed all the procedures in the retrospective review.

"Both lasers performed exceedingly well and had very satisfactory results," Dr. Dishler said. "There seemed to be a difference in that the number of patients who achieved 20/20 or better vision was slightly higher in the Zeiss group and that safety showed slightly better results in the Zeiss group as well, but I believe both platforms are very acceptable for clinical use."

In this study, he reviewed the records of 97 eyes treated with the VisuMax-MEL 80 workstation and 75 eyes treated with the Allegretto Wave Eye-Q-IntraLase FS60. Both of the excimer lasers have similar wavefront-optimized prolate ablation characteristics, a fact that has bearing on the comparability of results, he said.

Dr. Dishler said that no nomogram adjustments were made with the MEL 80 excimer system, whereas data from the Allegretto cases were entered into algorithm adjustment software.

The age and preoperative refraction of the patients in both groups were similar. The mean age for the VisuMax-MEL 80 group was 35 years, and it was 37 years for the Allegretto-IntraLase group. A slightly higher amount of sphere existed in the VisuMax-MEL 80 group (–2.74 D ± 1.63 versus –1.73 D ± 2.65), and a slightly greater amount of cylinder existed in the Allegretto-IntraLase group (–1.90 D ± 1.71 versus –0.81 D ± 0.55).

The results for postoperative refraction were quite similar between the treatment groups, Dr. Dishler said. At 1 month postoperatively, the manifest refraction spherical equivalent (MRSE) was –0.03 D ± 0.26 for the VisuMax-MEL 80 group and –0.08 D ± 0.45 for the Allegretto-IntraLase group. The range of results was wider in the Allegretto-IntraLase group than in the MEL 80 group (+1.25 to –2.00 versus +0.75 to –1.00), however.

"There's a little more scatter in the Allegretto corrections, but, on average, they are on target," he said.

At 3 months

At 3 months, the average results also were similar between groups but with somewhat more variability in the Allegretto-IntraLase group. The range in MRSE for the Allegretto-IntraLase group (n = 41) was +1.88 to –1.00 D, whereas the range in the VisuMax-MEL 80 group (n = 39) was +0.75 to –1.25 D. The outcomes for MRSE within 0.5 D of the attempted correction were similar, but, again, with slightly more scatter in the Allegretto-IntraLase group.

Results for uncorrected visual acuity (ETDRS) showed that a slightly greater percentage of patients in the Allegretto-IntraLase group had 20/15 vision, but more patients in the VisuMax-MEL 80 group had acuities of either 20/15 or 20/20. In addition, about 90% of patients in the VisuMax-MEL 80 group had 20/20 uncorrected visual acuity at 3 months, and 100% had 20/25 or better. A higher percentage in the Allegretto-IntraLase group had 20/15 acuity, but a slightly lower percent had 20/20 and 20/25; 100% of patients had acuity of 20/30 or better.

"The Allegretto performed a little better in some patients, but that group also had more patients who only had 20/25," Dr. Dishler said.

The safety results showed that at 1 month, 3% of eyes in the VisuMax-MEL 80 group had lost one line of best-corrected visual acuity (BCVA); no eyes had lost visual acuity at 3 months. In the Allegretto-IntraLase group, 2% had lost two lines of BCVA at 1 month postoperatively, and 17% of eyes lost one line of vision at 3 months.

More patients in the Allegretto-IntraLase group gained one line (34% at 3 months), however, and 7% gained two lines, whereas no patients in the VisuMax-MEL 80 group gained two lines.

"While the Allegretto group had more patients gain lines, it also had more patients lose lines; the VisuMax-MEL 80 was more neutral," Dr. Dishler said. "Nobody lost any lines, while 18% gained one line, and 82% stayed exactly where they were."

On a scatter plot, results showed more undercorrection and overcorrection for the Allegretto-IntraLase eyes, but the data for the Allegretto fit better with the theoretical "perfect" correction because of the nomogram adjustment, he said.

Additional research is needed to determine what effect the two femtosecond lasers might have had on the results, he added. Dr. Dishler said he is planning to expand the study with cross-matched femtosecond and excimer laser combinations.

The two femtosecond lasers operate in different parameter ranges, he said. Compared with the IntraLase, the VisuMax has tighter spot spacing, lower spot energy, and higher laser frequency. The VisuMax also uses a curved contact lens as opposed to the flap lens used on the IntraLase. Both femtosecond lasers cut flaps at the same depth.

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