Thursday, April 20, 2006

Customized Ablation #8: An AAO 2002 Update: Classic vs. Custom LASIK -- The Battle Continues

This is the 8th and final article in the series of eight articles chronicling the development of Customized Ablation or Wavefront Directed Lasik. This column was written following the2002 AAO meeting, and was published in the January1, 2003 issue of Ocular Surgery News (but was not put online).

Technology Update

An AAO 2002 Update: Classic vs. Custom LASIK -- The Battle Continues

Irving J. Arons
Managing Director
Spectrum Consulting

With the first customized ablation protocol approved by the FDA -- Alcon's LADARVision system with LADARWave diagnostics -- and several other companies six-month results reported and filed, the battle continues whether the market will turn to custom ablation over classic LASIK. As was pointed out during the "Catch the Wave" combined session of the ISRS and RSIG, the push toward custom ablation has raised the outcomes levels of standard or classic LASIK. With improved laser algorithms, use of eye trackers, improved microkeratomes, and better diagnostics for screening patients, classic LASIK results, especially wavefront-assisted LASIK (wherein the wavefront device is used for screening and planning the ablation) have risen to very high levels of uncorrected acuity and patient satisfaction. This, again, raises the question of the need for customized ablation.

The results obtained with customized ablation, regardless of the laser platform used are believed to be, in general, about 10% to 15% better than the results obtained with classic LASIK. However, because customized ablation treats higher orders of aberrations (coma, tilt and spherical aberrations), in addition to the lower orders of sphere, cylinder, and defocus, the quality of vision (contrast sensitivity and night vision) is dramatically improved. It is our believe (as well as of several other analysts) that custom ablation will aid in improving patient perceptions of the results that they might obtain and will serve as a catalyst toward driving procedure growth over the next several years. In fact, it could provide for a 13% to 15% growth in procedures in 2003, bringing the market back to the levels seen in 2000 before the recent slide in procedures occurred. This, of course, is dependent on a return of economic growth and consumer confidence.

From all appearances, the already approved classic LASIK laser systems -- the VISX Star S3, Alcon LADARVision, Bausch & Lomb Tecnolas 217z, and the Nidek EC5000 -- all appear to provide similar results. The limiting factor is now the wavefront diagnostics. Even though these systems have improved vastly over the last two years, there is no standardization and results on various systems on the same eyes are different. In a study reported by Erin Durrie Stahl during the ISRS pre-meeting, a set of 20 eyes were tested on six different wavefront and ray tracing diagnostics. Although the results were repeatable on each system, they were not comparable across systems. Standardization is truly needed.

In fact, not all systems can capture all eyes. In his presentations, Prof. Theo Seilor admitted that the Tscherning aberrometer (used with the WaveLight Allegretto and Schwind ESIRIS), did not capture 15%-20% of the eyes tested. And, similar results are reported with other systems, especially with abnormal eyes. More development and standardization is needed before wavefront diagnostics become the standard of care. Another open question is whether topography, to capture the curvature of the cornea, should be added to wavefront systems in order to obtain a complete picture of the aberrations of the eye. This is currently done by Bausch & Lomb, Nidek, and LaserSight (but the latter without the wavefront diagnostic as yet) -- and Carl Zeiss Meditec, Schwind, and WaveLight internationally.

And, Jack Holliday has been exonerated! After preaching for several years, the congregation has finally heard the message -- prolate corneas are indeed better than oblate (eagle eyes vs frogs!). Several laser manufacturers now incorporate algorithms that produce prolate shaped corneas (Carl Zeiss Meditec, WaveLight, and Schwind, for example) and are getting much improved outcomes.

As reported by Marguerite McDonald, MD, and others, the key to obtaining good customized ablations is going to be "registration, capture, match, and treat". The diagnostic device needs to be capable of registering the position of the eye, capture the abnormalities, match the eye registration in front of the laser, and be able to treat the abnormalities -- hopefully without inducing further aberrations.

The latter raises another question. Since the use of the microkeratome and customized ablation algorithms seem to induce some degree of higher order aberrations, will the use of "Advanced Surface Ablation" (as named by Dan Durrie, MD) make a comeback. In the past I have written extensively about the introduction of LASEK into refractive practice. According to recent conversations with Dave Harmon of MarketScope, surface ablation (PRK and LASEK) now account for between 2% and 3% of refractive procedures. This could increase dramatically if it is shown that surface ablations produce better results with customized ablations.

There is no question that customized ablation will be the wave of the future. It will provide better outcomes for previous poor results (decentered ablations, small optical zones, etc.) and produce better quality of vision with improved contract sensitivity and night vision. It will also reduce the need for retreats dramatically, as Manus Kraff, MD, said, "from about 10% down to less than 3%".

In questioning others about custom vs. classic, I asked how many of the patients coming into their practices and being evaluated on wavefront diagnostics had higher order aberrations that could be effectively treated with custom LASIK. Dr. McDonald estimated perhaps 20% of her patients, while Dr. Scott MacRae thought the split was more like 33% with higher order and 67% with lower order alone.

Further, improvements in diagnostics are also under development. VISX, with the aid of 20/10 Perfect Vision, is developing an adaptic optics version of its WaveScan. This will eliminate the need for the PreVue lens, wherein a customized ablation is put onto a plastic disc that can be mounted on a lens set and presented to a patient to show the improvement in vision that could be obtained with customized ablation. In the adaptic optics version, the improvement will be built into the WaveScan device and the patient can be shown the improvement in vision immediately while still sitting in front of the WaveScan. According to Julian Stevens, MD, Nidek and others are also working on this type of technology, along with research at the University of Zurich.

Improvements are also coming in the laser platforms. Although first promulgated by LaserSight (but not fully implemented into the U.S. market), faster small spot scanning lasers with matched faster eyetrackers are coming. Led by WaveLight's Allegretto, Schwind's ESIRIS, and Carl Zeiss Meditec's MEL 80, these lasers will provide shorter ablation times and better outcomes for normal eyes with lower order aberrations.

To put Alcon's custom ablation approval in perspective, the approval label was for up to -7 diopters of myopia, with a 0.5 diopter of astigmatism (as measured by manifest refraction). However, according to several doctors that we spoke with, patients with up to 1.5 diopters of astigmatism, as measured on the LADARWave diagnostic, can be treated. Higher astigmatism approval is not expected from the FDA for 4-6 months. But, according to Dan Durrie, MD, when questioned about the relatively low amounts of astigmatism approved, he said, "that would encompass 40%-50% of my patients".

Bausch & Lomb and VISX have both filed for custom ablation approval, with the FDA expected to give marketing approval to both sometime in the first half of 2003. Since both companies have filed for myopia with astigmatism, once they achieve approval, the playing field should be level for all three major companies.

As shown in two tables(1,2) produced following the meeting, it appears that the quality of the custom ablation data from the four competing firms for the U.S. market does not give any competitive advantage. But, since VISX has the largest installed base of laser systems, and already has its WaveScan in the hands of better than 80% of its laser owners, it may have a marketing advantage.

1. Comparison of Laser Systems for Customized Ablation, Source: Company information and Spectrum Consulting, November 2001.

2. Comparison of Wavefront Diagnostics, Source: Company information and Spectrum Consulting, November 2001, updated October 2002.

(Anyone wishing to obtain a copy of either table should request it from me via email.)


At 8:16 PM, Anonymous Anonymous said...

Your blog keeps getting better and better! Your older articles are not as good as newer ones you have a lot more creativity and originality now keep it up!


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