Wavefront-optimized ablation promising

February 15, 2005

New Orleans—The Allegretto Wave excimer laser (WaveLight Laser Technologie AG, Erlangen, Germany) received high marks from users who covered its various features during the American Academy of Ophthalmology annual meeting.

What sets the Allegretto system apart from other approved laser systems is its speed, non-dilating eyetracker, and wavefront-optimized algorithm. The superior outcomes that have been achieved with this platform add up to lower enhancement rates and greater patient satisfaction, explained Michael Gordon, MD, a private practitioner in San Diego.

This flying spot laser, using a Gaussian beam with a diameter of 0.95 mm, is one of the fastest on the U.S. market with a pulse frequency of 200 Hz. Its eyetracker is able to track all saccadic eye movements and does not require dilation. It can track pupils from 1.8 to 10 mm in diameter. The treatment can be manually decentered if necessary, he said.

"First, the laser uses an advanced form of the Munnerlyn formula where keratometry actually enters into how many pulses are delivered. Most lasers that we use do not incorporate those data," Dr. Gordon said.

Creating a prolate shape The ablation profile created with the Allegretto is unique because it concentrates more energy at the periphery of the cornea to create a more prolate shape, he continued. The problem with treating a 6- or 6.5-mm optical zone is that the beam hits peripherally on the curved surface, becomes an oval, and energy is lost.

With wavefront optimization, surgeons can now produce an aspheric ablation. "This minimizes the spherical aberration that is induced with traditional LASIK surgeries," he said.

While wavefront-optimized treatments are not the same as customized wavefront-guided procedures, the results for normal corneas are similar, according to David T.C. Lin, MD, clinical assistant professor, University of British Columbia, Vancouver.

"Using either wavefront-optimized or wavefront-guided treatment for normal corneas, 20/20 uncorrected visual acuity is achieved in 90% of cases," Dr. Lin noted. "So why would you use custom treatment on a normal cornea when the wavefront-optimized one works so well?"

He explained that with the old excimer laser technology, standard treatment of the cornea involved treating the central and peripheral areas with the same type of energy. This produced a more oblate shape because of "tangential loss at the edges. Wavefront-optimized treatment places more pulses to compensate for this, making the cornea relatively less oblate and more prolate," he said.

For most of Dr. Lin's cases, he uses wavefront-optimized treatments with the Allegretto Wave laser. However, some eyes with abnormal corneas and irregular astigmatism will need to be treated with customized wavefront-guided procedures. In Canada, the Allegretto platform can be used to treat abnormal or irregular corneas either with customized wavefront or customized topographically linked algorithms. At the moment, custom treatments using the Allegretto Wave excimer system cannot be performed in the United States, but the next-generation technology using the Allegretto platform is expected to accomplish this at a faster speed of 400 Hz, Dr. Lin said.