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How WFG ablations compare


In a comparison of two wavefront-guided excimer lasers, one platform provides better clinical results on some measures but cannot image certain eyes. The other system can image nearly all eyes, but has slightly less robust clinical results.


In a comparison of two wavefront-guided excimer lasers, one platform provides better clinical results on some measures but cannot image certain eyes. The other system can image nearly all eyes, but has slightly less robust clinical results.


Dr. Manche

Stanford, CA-Multiple trials suggest that wavefront-guided (WFG) excimer ablations yield better results for myopic LASIK than wavefront-optimized (WFO) procedures. But how do WFG ablations compare?

A recent head-to-head comparison found that while one excimer laser unit (Allegretto Wave Eye-Q 400 Hz, Alcon Laboratories) produced slightly better results for some clinical outcome measures than a similar excimer platform (VISX CustomVue S4IR, Abbott Medical Optics), the latter unit was easier to use and could be used on eyes the first unit could not image.

“The take home is that you had excellent safety in both groups,” said lead author Edward E. Manche, MD, director of refractive and cornea surgery and professor of ophthalmology at the Byers Eye Institute, Stanford University School of Medicine, Stanford, CA.

“No eyes lost more than one line of best-corrected visual acuity (BCVA),” he said. “We had gains in both groups that were essentially equivalent, with almost 50% gaining one or more lines of BCVA.

“The caveat is that it’s very difficult to obtain good quality images on the Allegretto,” Dr. Manche said. “You can only image about three-quarters of the eyes on the Allegretto machine preoperatively. Postoperatively, it was even more difficult.”

Dr. Manche has conducted a number of prior studies using both WFG and WFO platforms from multiple manufacturers.

“What we’ve found in our previous studies was that WFG ablations yielded better results than WFO on both the VISX and the Allegretto,” he said. “If WFG is better than WFO on both machines, it was only logical to compare WFG ablations on the two platforms.”

The prospective, randomized, contralateral study treated both eyes in 50 subjects, a total of 100 eyes. One eye of each patient had WFG LASIK with the Allegretto excimer laser. The contralateral eye had WFG LASIK with the VISX CustomVue S4IR excimer laser. The eyes were randomly assigned by ocular dominance and all LASIK flaps were constructed using an AMO Intralase IFS 150-kHz femtosecond laser.

Eyes in the two groups were closely matched by age, gender and most visual measurements. The only statistically significant difference was slightly worse myopia in the CustomVue group, -4.18 compared with -3.89 in the Allegretto group.

One year after surgery, the two groups were statistically identical in terms of residual spherical equivalent and residual cylinder, Dr. Manche reported. But there were significant differences in higher order aberrations at one month (p = 0.04) and at 12 months (p = 0.01). The Allegretto eyes went from 0.38 microns preoperatively to 0.33 microns after surgery compared with 0.37 microns preoperatively in VISX eyes to 0.40 microns after surgery. Trefoil was reduced by similar amounts in both groups. Coma was unchanged in the Allegretto group and increased slightly in the CustomVue group. Spherical aberration decreased in the Allegretto group and increased in the CustomVue group.

Predictability was better in the Allegretto group at three months (p = 0.04), at 6 months (p = 0.02) and at 12 months (p = 0.04).

Best uncorrected visual acuity was similar in the two groups at 1 month, 3 months, and 12 months, but was significantly better in the Allegretto group at 6 months (p = 0.04). There was no statistically significant difference in BCVA between the two groups.

The biggest difference between the two groups was subjective clarity. Patients judged their Allegretto-treated eyes better both during the day (p = 0.005) and at night (p = 0.001) compared to their CustomVue-treated eyes.

At the same time, there was no clear patient preference for one platform over the other. About 23% of patients preferred both Allegretto and CustomVue, just under 45% had no preference and the balance were unsure which they preferred.

While Allegretto offered statistically significantly better outcomes on several measures, patients themselves had no preference for one treatment over the other, Dr. Manche said. The two surgeons, however, had very clear preferences.

“We imaged the patients on both machines preoperatively and postoperatively,” he said. “Preoperatively, we obtained images of 100% of the eyes on the VISX Wavescan aberrometer but could only obtain images on 70% to 75% of the eyes on the Allegretto Allegro Analyzer aberrometer. It is very difficult to obtain good quality images on the Allegro Analyzer and the ones we obtained often took an extremely long time. Most people who use the Allegretto use the WFO treatment ablations because  the Allegro Anayzer is difficult to use.”

That puts clinicians in a bind. The Allegretto produces better results for certain clinical outcome meaures, but imaging can be difficult to impossible. The CustomVue results are slightly lower for certain outcome measures, but imaging rarely fails.

“I do 100% WFG procedures,” Dr. Manche said. “If I can’t image someone on the Allegretto Allegro Analyzer, I take them to the VISX Wavescan. The VISX Wavescan can image almost anyone with the exception of patients with very small pupils or corneal scarring. It is an extremely robust system.”

Edward E. Manche, MD

E: eemanche@yahoo.com

Dr. Manche has no financial disclosures that relate to this story.


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