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Wavefront-guided, -assisted, -adjusted: Choosing the right approach
Refractive surgeons must learn the distinctions among a host of options to know what type of correction to offer their patients.
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In the coming year, the availability of new modes of wavefront-guided ablation will enable surgeons to expand their laser vision correction options. These modes will soon include wavefront-adjusted, wavefront-assisted and wavefront-guided ablation, in addition to the conventional ablation protocols already available.
“The question becomes, who should be treated with which type of platform?” said Karl G. Stonecipher, MD, in a recent interview. “We need to determine who is a good candidate for LASIK and who is a good candidate for wavefront-guided LASIK. These are questions that every refractive surgeon has to face.”
The decision is not as clear-cut as simply a choice between standard LASIK and custom LASIK. The division lines have blurred, as information generated with wavefront diagnostic technology has trickled down into many aspects of standard LASIK — from diagnostics to treatment algorithms to ablation.
This article, the fourth in our series on customized ablation and wavefront technology, explores the differences between wavefront-guided, -assisted and –adjusted ablation and what they will mean for surgeon choices and patient care.
Wavefront-adjusted LASIK
“There is no standard LASIK anymore,” Dr. Stonecipher said. “All LASIK systems today have wavefront-adjusted treatment profiles or programs otherwise modified from the originals that came out in the mid-1990s.”
The term “wavefront-adjusted LASIK” was coined by Theo Seiler, MD, PhD. At the 2002 American Academy of Ophthalmology meeting in Orlando, U.S.A., Dr. Seiler asserted that a new generation of excimer laser corneal ablation systems are guided by wavefront principles. Therefore, they should be referred to as “wavefront-adjusted.”
“In 1998, I proposed a wavefront-adjusted profile of LASIK because most of my patients were not satisfied with the quality of vision they had after LASIK,” Dr. Seiler said. “They complained of poor night vision.”
Dr. Seiler and colleagues at the University of Zurich discovered that conventional LASIK, which treated only spherical and cylindrical error, induced aberrations that caused night vision problems. The researchers collected data on these induced aberrations and attempted to develop, with wavefront technology, a new algorithm for standard LASIK systems that would reduce the amount of spherical aberration induced.
“Dr. Seiler added a ‘fudge factor’ to standard LASIK for the amount of spherical aberration that the average patient has or will get after LASIK,” said Jeffrey J. Machat, MD, a Toronto-based refractive surgeon who was an early adopter of wavefront technology. He has performed wavefront-adjusted and wavefront-guided LASIK on more than 3,000 eyes since March 2000.
According to Dr. Machat, Dr. Seiler determined the average amount of spherical aberration that standard LASIK induced in a typical healthy patient and compensated for it with a modified wavefront algorithm.
“This correction aims for a prolate cornea with a Q value, or aspheric factor, of –0.46, to compensate for the aberrations,” Dr. Seiler said. “We altered the format to compensate for, and correct, induced spherical aberration.”
In the late 1990s, this new, wavefront-adjusted algorithm was introduced into WaveLight Laser Technologie’s Allegretto Wave excimer laser, now distributed by Lumenis.
The prolate principle
“At the time, many surgeons were seeing that the old lasers weren’t working well,” Dr. Stonecipher said. “People had many complaints. So surgeons began telling engineers what was wrong, and engineers began to adjust the profile to amend the problems.”
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One such surgeon was Jack T. Holladay, MD, MSEE, FACS, a refractive surgeon from Houston, Texas, who has been a champion of the concept of the prolate cornea. Dr. Holladay maintains that a prolate corneal shape — rather than an oblate shape — produces better vision.
“Dr. Holladay realized that this was a big issue. People needed prolate corneas to see better,” Dr. Machat said. “He realized that people were not just having night vision problems, but poor vision quality problems overall, because of oblate corneas created by standard LASIK.”
“Dr. Holladay was really the champion for this cause,” Dr. Stonecipher agreed. “He kept saying, ‘Let’s keep the natural prolate shape of the cornea and still treat the patients.’ After a while, engineers listened, and it worked.”
Dr. Holladay’s interest in the prolate corneas was recognized in the development of the AstraMax with AstraPro ablation-planning software for the LaserSight LaserScan LSX excimer laser and ablation system. The AstraPro software enables surgeons to perform ablation with an increased optical zone, preserving the prolate shape of the cornea.
The observations of Drs. Holladay and Seiler have led other manufacturers to modify their excimer laser systems’ software based on similar principles.
“Basically every system out there today has been modified with wavefront technology,” Dr. Stonecipher said. “Manufacturers have adjusted their treatment profiles to help do a better LASIK treatment to begin with, before wavefront-guided ablation is ever called upon.”
Other modifications
Dr. Machat calls these wavefront-adjusted ablation systems — such as the Lumenis Allegretto and the AstraPro system from LaserSight — aspheric ablation systems.
“An aspheric system is a wavefront-adjusted LASIK system that corrects the average amount of spherical aberration that patients have, while preserving a prolate cornea,” Dr. Machat said. “It is a type of wavefront-adjusted LASIK treatment that does not utilize a wavefront sensor but is still a modification of a standard LASIK system.”
However, Dr. Machat pointed out that “just because a LASIK system doesn’t have a wavefront adjustment, it doesn’t mean that the laser hasn’t had other modifications made to its standard patterns over the years.”
Dr. Machat noted that the Visx Star S4 ActiveTrak laser, with a variable spot scanning system and an extended ablation zone of up to 8 mm, is one such ablation system that has not incorporated wavefront technology into its algorithm.
“I am using the Visx S4 now with SmoothScan technology, and I am just amazed at the results compared to when I used it several years ago,” Dr. Machat said. “I get extremely good coverage for the overall majority of the patient population in terms of their pupil size, and good quality night vision.”
Dr. Machat believes that this modified approach to standard LASIK works well for nearly all of his patients.
“The majority of patients are going to do absolutely wonderfully with a standard laser vision correction procedure, probably about 95%,” he said. “Statistics show that lasers are much more sophisticated now — whether modified with wavefront technology or not. The programs are excelling, the smoothness of the ablation is refined, and the advanced eye trackers are superb. We can now offer a great procedure to the majority of the population.”
Wavefront-assisted LASIK
Arun C. Gulani, MD, agreed. “Most of the time you can get excellent results from LASIK that is not guided by wavefront technology,” he said.
But wavefront can also be used effectively as a freestanding diagnostic tool, Dr, Gulani said. “Wavefront can help you decide who you should not work on. You might discover that the patient will end up with poorer night vision and additional aberrations after LASIK,” he said.
In fact, according to Dr. Machat, wavefront technology can be a useful tool in catching warning signals that are not detected by standard diagnostic tools. In his practice, he allows wavefront to “assist” some of his LASIK treatments by running a wavefront scan before LASIK to catch refractive error not picked up by conventional refractometers.
He said this “wavefront-assisted” approach can be a beneficial addition to standard LASIK.
“We have been surprised in our practice to find that a patient will actually get a better visual postoperative result after running a wavefront scan than they would have if we had done a standard approach and gone with our own numbers,” Dr. Machat said.
He cited an instance in which a LASIK candidate underwent standard tests, including cycloplegic and manifest refraction and topography.
“Everything correlated, but then we did a wavefront analysis and picked up more astigmatism. So we put those figures into the phoropter for the patient. After surgery, the patient actually saw better than with their glasses,” Dr. Machat said.
Wavefront-guided LASIK
Despite these other approaches, Dr. Machat believes that ultimately wavefront-guided LASIK will be the most beneficial technique for all patients.
“All patients will benefit from wavefront-guided treatments regardless of their current vision,” Dr. Machat said. The only patients who might not benefit, he said, would be older patients who are undergoing lenticular changes or patients with corneal opacities that would obscure a wavefront reading.
“In most cases,” he said, “the patient’s final result will be more predictable, they have a greater chance of improving best corrected vision, and even if they don’t improve best corrected vision, they experience a better quality of vision.” Dr. Machat added that the quality of vision after wavefront-guided LASIK is especially good under low-light conditions, and contrast sensitivity is preserved.
“Patients will also experience a faster recovery of their contrast sensitivity,” Dr. Machat said. “So I think that the benefits to having custom ablation are multiple. There are a lot of refined benefits to having this type of treatment.”
While Dr. Machat said 95% of his patients would have excellent results from LASIK without wavefront guidance, he said there is that 5% that need wavefront-guided ablation.
“About 5% of my patients absolutely require it to treat existing higher-order aberrations that cause unsatisfactory night vision,” he said.
Who to treat, how to treat
With all the above treatment choices available for laser refractive surgery, finding the right approach for the patient can be challenging.
“What we need to do as medical professionals is come together, pool our data and decide what is normal and what is abnormal in terms of aberrations,” Dr. Gulani said. “We need to say, ‘If you see this, you must treat it with conventional LASIK. If you see that, you should use wavefront-guided LASIK. If you find this, then please don’t touch the cornea.’”
Dr. Gulani said that just because a patient has optical aberrations, this does not necessarily mean those aberrations should be removed.
“Some aberrations might be helpful. We need to determine what is good and bad, so that we can get on one platform and use a universal language for this technology,” he said.
(For a more detailed discussion of “good” and “bad” aberrations, see the previous installment in this series in the March issue.)
Dr. Stonecipher agreed. “We haven’t worked out the mitigating factors of who to treat, how to treat, what to treat and what we’ve got when we are done,” he said. So far, surgeons are treating patients based on the limited literature available on wavefront and their own clinical experience, he said.
Guidelines from experience
“To determine how to treat a patient, I look at the wavefront maps and Zernike polynomials for higher-order aberrations,” Dr. Seiler said. “If the patient has about 0.2 µm of myopia, then they are, at first glance, a candidate for wavefront-guided LASIK.”
Dr. Seiler then looks more closely to see what types of aberrations the patient has.
“If there is mostly spherical aberration, we are going to correct all the aberrations. If there is only a certain amount of vertical coma, we leave it like it is – we don’t correct for that one because sometimes it is not indicative of poor vision.” For other types of aberration — higher-order errors such as trefoil — wavefront-guided LASIK is performed, he said.
“Our first goal is to try to preserve the wavefront patterns that patients have, and our second goal is hopefully to improve upon Mother Nature,” said Marguerite B. McDonald, MD. As the first U.S. ophthalmologist to use Alcon’s LADARVision system for wavefront-guided ablation, Dr. McDonald has already had extensive experience with wavefront technology.
“When you get someone with very low higher-order aberrations and he is very nearsighted, he is more likely to complain if he has an increase in higher-order aberrations after conventional LASIK,” Dr. McDonald said. “This is because the patient is so used to exquisite optics.”
In contrast, she said, another patient who is also very nearsighted — but is used to night vision problems due to excessive higher-order aberrations — might be completely satisfied with conventional LASIK, she said.
“This patient is used to poorer vision, so he thinks that this is how the world looks. He might not notice too much if you give him a standard ablation because he is used to crummy optics,” Dr. McDonald said.
The beauty of wavefront, she noted, is that if you do wavefront-guided ablation on a patient who has had poor optics all his life you can improve the optics to a level he or she has never experienced.
“It’s amazing,” she said, “you open up a whole new world for them.”
Enhancements
While many patients may desire wavefront-guided LASIK for its potentially exquisite optical results, the procedure may not be indicated for all these patients depending on the country in which they live.
For example, in the United States, only one device is currently approved for performing wavefront-guided LASIK: Alcon’s LADARVision system. That system is approved for myopia of up to 7 D with less than - 0.50 D of astigmatism.
Therefore, patients with high myopia are not currently candidates for wavefront-guided LASIK in the United States. For the time being, Dr. McDonald suggests that highly myopic candidates wait for wavefront to be approved for higher myopia. To temporarily minimize night vision problems, Dr. McDonald prescribes a pupil constrictor to patients who are bothered by the symptoms.
Dr. Machat, who in Canada is not subject to the same regulatory restrictions, treats high myopes differently. He suggests a two-step procedure. He first performs a modified conventional or wavefront-adjusted LASIK procedure on the patient to correct the high myopia (of greater than 7 D, with astigmatism greater than 3 D). He then later performs wavefront-guided LASIK as a custom enhancement.
“As a second step, I will do a customized ablation after standard LASIK to correct any residual higher-order aberrations or residual refractive error,” Dr. Machat said. “Typically, after these two procedures, the patient’s vision will be far better than if I just treat their residual refractive error with a standardized program.”
Tomorrow’s LASIK
As custom ablation becomes more advanced, and more wavefront devices become available to treat higher degrees of myopia, some surgeons believe that such two-step procedures will become refined into one, and wavefront-adjusted and wavefront-assisted LASIK will be replaced by wavefront-guided LASIK for all candidates.
“For the time being, all of these wavefront-incorporating LASIK procedures – wavefront-guided, wavefront-assisted and wavefront-adjusted — will coexist for a while,” Dr. Machat said. “However, as time goes on, there will be a clearer movement towards wavefront-guided procedures for everybody.”
Dr. McDonald agreed. “I think that all LASIK procedures will become customized, and standard LASIK, as wonderful as it is, will disappear. There is no question that wavefront is a better way of improving on an already great procedure.”
For Your Information:
- Arun C. Gulani, MD, is director of refractive surgery and chief of cornea and external disease in the department of ophthalmology of the University of Florida-Jacksonville. He can be reached at 580 West 8th St., Jacksonville, FL 32209-6561 U.S.A.; +(1) 904-244-9393; fax: +(1) 904-244-9399; e-mail: arungulani@aol.com.
- Jeffrey J. Machat, MD, can be reached at 181 Bay St., Suite 150, Toronto, ON, Canada M5J2T3; +(1) 416-362-2733; fax: +(1) 416-362-1370. Dr. Machat has a direct financial interest in Tracey Technologies.
- Marguerite B. McDonald, MD, can be reached at the Southern Vision Institute, 2820 Napoleon Ave., Suite 750, New Orleans, LA 70115 U.S.A.; +(1) 504) 896-1240; fax: +(1) 504-896-1251; e-mail: mbm2626@aol.com. Dr. McDonald is a paid consultant for Alcon Summit Autonomous.
- Theo Seiler, MD, PhD, can be reached at at Institut fur Refraktive und Ophthalmo-Chirurgie, Zolliker Strasse 164, CH-8008 Zurich, Switzerland; +(41) 43-488-3800; e-mail: theo.seiler@iroc.ch.
- Karl G. Stonecipher, MD, can be reached at Southeastern Laser and Refractive Center, 3312 Battleground Ave., Greensboro, NC 27410 U.S.A.; +(1) 336-282-5000; fax: +(1) 336-282-5022; e-mail: StoneNC@aol.com.
- Alcon, manufacturer of the Autonomous excimer laser and LADARVision system, can be reached at 6201 South Freeway, Fort Worth, TX 76134 U.S.A.; +(1) 817-293-0450; fax: +(1) 817-568-6142.
- Bausch & Lomb, manufacturer of the Technolas 217A and Zyoptix custom ablation system, can be reached at 1400 N. Goodman St., Rochester, NY 14609 U.S.A.; +(1) 585-338-6536; fax: +(1) 585-338-0898; Web site:www.bausch.com.
- LaserSight Technologies, manufacturer of the LaserScan LSX excimer laser and AstraMax, AstraPro systems, can be reached at 3300 University Blvd., Suite 140, Winter Park, FL 32792 U.S.A.; +(1) 407-678-9900; fax: +(1) 407-678-9981.
- Lumenis, distributor of the Alegretto excimer laser from WaveLight, can be reached at 2400 Condensa St., Santa Clara, CA 95051 U.S.A.; +(1) 408-764-3000; fax: +(1) 408-764-3660.
- Visx Inc., manufacturer of the Star S3 ActiveTrak laser and WavePrint custom ablation system, can be reached at 3400 Central Expressway, Santa Clara, CA 95051-7122 U.S.A.; +(1) 408-733-2020; fax: +(1) 408-773-7278.