spotlight on technology and technique
How Important is Custom Ablation?
A newly approved laser produces results as good as wavefront-guided -- without individual wavefront data.
By Christopher Kent, Senior Associate Editor

There's no question that wavefront-guided lasers have improved outcomes for many patients. Understandably, this has led many eyecare professionals to conclude that a customized, wavefront-guided ablation -- capable of correcting higher-order aberrations -- produces a better result than a non-customized ablation.

However, wavefront-guided ablation may be a less significant factor than previously thought. In fact, the improved results produced by many wavefront-guided lasers may only be partly attributable to the added wavefront data.

The Allegretto Wave Excimer Laser (manufactured by Wavelight, distributed by Lumenis, and recently approved by the FDA) is giving credence to an alternate possibility. By correcting some fundamental problems common to most refractive lasers, the non-wavefront-guided Allegretto is producing outcomes as good as, or better than, those produced by wavefront-guided systems -- without the extra time, effort and expense involved in using wavefront technology.

Clinical Data

Already very popular outside the United States, the Allegretto is the first system to receive concurrent FDA approval for myopia (up to -12 D, with astigmatism up to -6 D) and hyperopia (up to +6 D, with astigmatism up to +5 D, not to exceed a mean spherical equivalent of +6 D).

In the FDA trials -- which were done without personal nomogram adjustments -- 901 myopic eyes and 290 hyperopic eyes were treated. Among the myopes:

• at 3 months post-op, 84.8% were within 0.5 D of target; 96.7% were within 1 D.
• 57.5% gained one or more lines of UCVA; 36.3% remained unchanged. Only 5.7% lost one line, and less than 1% lost 2 lines.
• Only 5 out of 901 eyes required enhancement, and higher myopes (over -7 D) had results that were just as good as lower myopes.

At one year, 87.4% saw 20/20, 55.5% saw 20/16 or better, and 99% saw at least 20/40. Remark-ably, the retreatment rate at 1 year was 3.6%.

Results for the hyperopic eyes:

• 72.3% were within 0.5 D of target at 6 months post-op; 90.4% were within 1 D.
• 41.4% gained one or more lines; 48.5% were unchanged; 8.9% lost 1 line, and 1.5% lost 2 lines.
• At 6 months, 67% were 20/20 or better; 99% saw at least 20/40.

The Allegretto Wave Excimer Laser from Lumenis

The "Wavefront-Optimized" Advantage

How can a non-customized treatment produce results as good as, or better than, wavefront-guided lasers? And if wavefront-guided treatment isn't the key factor it has appeared to be, why have results improved so much when other lasers have switched to being wavefront-guided?

The first question can be answered by looking carefully at the design of the Allegretto. Perhaps most notably, the Allegretto compensates for the effect of corneal curvature on the ablating power of the laser beam. As the laser is aimed further from the center, increasing corneal curvature changes the angle at which the beam is striking the tissue. (See illustration, page 88.) This decreases the laser's effectiveness, just as the sun heats less effectively when it's lower in the sky.

Most laser systems don't compensate for this, so they remove less tissue away from the center of the cornea. The resulting corneal shape is oblate -- flatter in the center. This increases spherical aberration, causing night vision problems.

The Allegretto Wave takes into account the angle of the beam relative to the corneal surface. It uses a "wavefront-optimized" ablation profile -- an algorithm based on empirical wavefront research designed to optimize corneal asphericity -- that adjusts the number of spots being applied. The result is a more prolate cornea and an accurate, topographically visible optical zone that extends out to 6.5 mm. (See image, page 90.) Compensating for this factor also creates a smoother junction between treated and non-treated areas.

Notably, studies have shown that the Allegretto produces significant subjective improvements in glare, halo and low-light vision (as determined by pre- and post-surgery questionnaires). These unusual results are almost certainly explained by the more prolate shape and extended optical zone it creates.

The Upgrade Factor

A likely answer to the second question -- why the wavefront-guided versions of other lasers produce so much better results -- is offered by Raymond Stein, M.D., FRCSC, who practices in Toronto. Dr. Stein has used an Allegretto since June 2002. He says he now does 99% of his cases with the Allegretto.

"The wavefront-guided versions of most lasers haven't just added a wavefront-guiding system -- they've made significant improvements to the laser," he says. "They've improved their nomograms, made the curvature of the ablation more prolate and enlarged their optical zones. Some have made even more fundamental improvements.

"To determine how much the wavefront technology is actually doing, the laser companies would have to compare their custom lasers with the same lasers minus wavefront data, instead of comparing them to their earlier lasers, which were substantially different."

Features and Benefits

The Allegretto Wave features:

A fast and accurate ablation. This is the result of:

• a 0.95-mm spot, delivered in a gaussian beam profile to smooth the ablation
• closed-loop energy control for stable delivery
• a nitrogen-purged beam path designed to improve delivery and extend the life of the components
• a 200-Hz ablation rate that removes one diopter every 4 seconds -- the fastest currently available in the United States
• a depth indicator for measuring test ablations to ensure proper energy calibration
• tissue-saving nomograms that produce accurate results while minimizing tissue removal
• a 200-Hz active eyetracker with a response time of 6 to 8 milliseconds (depending on eye movement). It tracks pupils up to 8 mm in diameter, without dilation, and automatically locks onto the pupil -- with no buttons to press.
• an integrated plume evacuator. Studies done by other researchers have shown that firing a laser through an ablation plume interferes with energy delivery, undermining accuracy. (Numerous anecdotal reports also suggest that breathing the plume may affect the health of those working in proximity.)

Design advantages. These include:

• a Zeiss microscope and built-in slit lamp. The slit lamp can be moved into the surgical field, making it easy to check the eye for striae or debris, or to locate the flap edge when performing enhancements.
• a small footprint; the laser fits through standard doorways.
• Doctors report that maintenance is minimal, and the laser is easy to calibrate -- much like a YAG laser.

Service advantages. Lumenis provides a full warranty for the first year, including all consumable optics, and has a separate service and support organization that focuses exclusively on meeting the needs of refractive customers.

	As the laser angle increases toward the periphery of the cornea, the same energy is spread over a larger area, and more is reflected away. The Allegretto compensates for this by applying more pulses.

Feedback From the Field

Charles R. Moore, M.D., who practices in Houston, was a participant in the clinical trials, but has also done his own research. "I did a study comparing 50 wavefront-guided cases using a popular laser to 50 'wavefront-optimized' Allegretto cases," he says. "The Allegretto's results were better. And after more than 300 cases I have a 1% en-hancement rate with the Allegretto; I have a 15% enhancement rate with my wavefront-guided patients.

"The most important thing for our practice is that the ranges of approval for the Allegretto so far exceed those of wavefront-guided lasers. Only 15% to 25% of the pa-tients we see qualify for wavefront-guided LASIK -- but 95% qualify for treatment with the Allegretto."

Dr. Moore notes that Allegretto patients have a much faster rehabilitation. "Also, we've found a statistically significant improvement in halo and glare issues after treatment. This is more common in patients who have less than 7 diopters of myopia, but we see it across the board.

"Perhaps the biggest difference between this and other lasers is the tracker," he adds, "which has a 6- to 8-millisecond response time. Any tiny movement of the eye is immediately picked up, and tracker failures have been almost unheard of. The laser is fast, too; it treats one diopter of myopia every 4 seconds, and 1 diopter of hyperopia every 10 seconds. One diopter of hyperopia with our other laser takes 30 to 40 seconds."

Dr. Stein agrees that it's hard to compete with the standard Alle-gretto ablation. "It has a very fast rate: 200 hertz. If the procedure takes a long time, as some lasers do, the cornea can dry in certain areas and not others, affecting the quality of the outcome. Also, the tracker's been great. We've done more than 3,000 cases with the Allegretto since June 2002, and I haven't had a single case I couldn't track, including patients with nystagmus.

"The working distance is very nice. It gives you a lot of room to cut and manipulate the flap -- more so than other laser systems I've used. It also has a fabulous optical system with a slit lamp attached to the laser, so visibility of the flap and underneath the flap is excellent. It's the only laser I know of that's like this."

Dr. Stein has also been impressed by the laser's consistency and durability. "It's a real workhorse
. . . it hardly ever goes down. It has very stable fluence, and recovery of vision is very rapid because the ablation is very smooth. Our technicians love using the machine.

"It's exciting technology. I get a lot of calls from U.S. surgeons who are not only interested in using the Allegretto, but interested in having their eyes treated with it!"

Karl G. Stonecipher, who practices in Greensboro, N.C., says his experience has been similar. "When I compared my Allegretto patients head to head with my wavefront-guided patients, the Allegretto patients did much better. Also, before my Allegretto came I could only treat about 1 out of 4 patients. I can treat nearly everybody with the Allegretto, except for mixed astigmatism."

Dr. Stonecipher points out that the Allegretto is more expensive than other lasers. "However," he adds, "the per-use fee for a custom treatment with our other laser is $250; the fee for the Allegretto is $150 because it's not wavefront-guided. So you save $100 per case from that standpoint.

"I think it's one of the best laser platforms I've had the opportunity to work with."

For More Information

To find out more about the Allegretto Wave Excimer Laser, call 1-866-7-ALLEGRETTO, send an e-mail to info@allegrettowave.com, or visit www.allegrettowave.com on the Web.

What about Wavefront-Guided Allegretto? How much difference does wavefront-guided treatment really make? The Allegretto is a good candidate for answering this question because, unlike most companies' wavefront-guided lasers, which are substantially different from their basic lasers, the identical laser is doing both versions of treatment. Wavefront-guided treatment with the Allegretto isn't yet approved in the United States. However, Matthias Maus, M.D., who practices in Cologne, Germany, has reported good results using the Allegretto in concert with the Wave Analyzer (which uses the Tscherning principle) to perform custom ablation. During one of Dr. Maus' Allegretto studies involving 48 patients, a subset of 16 patients (all myopes) received wavefront-guided treatment in one eye and non-guided treatment in the other. (Half received the guided treated in the dominant eye, half in the non-dominant eye, and neither the technician nor the patient knew that there was any difference in the treatments being performed.) The result? Any measurable difference between the eyes was minimal. Thirteen of the patients had slightly better contrast sensitivity in the wavefront-guided eye, but Dr. Maus couldn't find any substantial difference in visual acuity resulting from the different treatments. However, asked which eye they preferred, all 16 patients chose the eye that received wavefront-guided treatment! Dr. Maus was unable to explain this based on his examinations, but the message seems clear: Wavefront-guided ablation may not be as big a factor in improving outcomes as it has appeared to be -- but it does make a difference. Topography of an Allegretto patient shows the true, large optical zone produced by the laser.