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Wavefront-Guided vs. Wavefront-Optimized Ablations
Differentiating terms and techniques.
BY JOHN PARKINSON, ASSOCIATE EDITOR

The Allegretto Wave 200 Hz laser with the Allegro Analyzer was recently FDA-approved for wavefront-guided laser ablation.

A few years ago, the American Society of Cataract and Refractive Surgery (ASCRS) decided to define the terms "wavefront-guided" and "wavefront-optimized" in order to provide clarity on the two different types of ablation. According to ASCRS, "Wavefront-guided vision correction procedures customize laser treatments based on the individual characteristics of the eye that is being corrected. The term wavefront-optimized refers to laser treatment software that has been designed with certain corrections pre-programmed, although a true and customized wavefront plan is not employed."

While these definitions do a good job of answering the theoretical differences, questions remain about the clinical differences such as, how do the mechanisms of action work? What type of correction will each system produce? And what type of results can be expected?

This article will attempt to describe the differences between the two technologies, identify who the best surgical candidates are for the procedures and explain how surgeons are positioning each procedure in their practices. 

Is There Still Room for Conventional Ablation?

Surgeons vary on their stances about employing conventional ablation. Some still use it frequently, while others have chosen to do away with it almost entirely. Although Bernard Milstein, M.D., prefers wavefront-guided ablation overall, he still uses conventional ablation for patients who have mostly lower-order aberrations.

"We are able to diagnose the higher-order aberrations (HOA) much more rapidly, so we can determine those patients who really need to have wavefront-guided ablations as opposed to those who do not," states Dr. Milstein.

The newly approved LADAR6000 excimer laser from Alcon incorporates new features to help improve consistency and patient flow.

Mark Whitten, M.D., uses conventional ablation only for enhancements and patients who request it; otherwise, his preference is to perform wavefront-guided procedures. Patients who wish to have conventional ablation sign a release form stating they know a better procedure exists. Dr. Whitten believes that wavefront-guided and wavefront-optimized ablations better serve patients and are the second generation of such technologies. 

"All of these software changes are basically an evolution of the improved outcomes," states Dr. Whitten. "Conventional is a first-generation system."

In his preoperative discussions with surgical candidates, Dr. Whitten goes over the FDA results of a study of one manufacturer's laser using conventional ablation and comparing its wavefront-guided software for the same laser to solidify the argument for wavefront-guided procedures. The FDA study showed that many of the patients who had HOAs preoperatively had many of their night glare and halo issues resolved after wavefront-guided surgery.

Charles Moore, M.D., is now using wavefront-optimized exclusively, and in his preop speaks with refractive surgery candidates, he talks to patients about functional vision and the possible shortcomings of conventional ablation. "We explain to them that in the past, 20% to 25% of patients had night-driving problems," says Dr. Moore.

It is important to note that most surgeons report that the majority of their patients who have had LASIK with conventional ablation remain satisfied. William Bond, M.D., says he sees patients today who had conventional LASIK 10 years ago and are still very happy with the results. Steve Brint, M.D., has also had longtime patients who are satisfied with their conventional LASIK corrections.

The Zyoptix Diagnostic Workstation, with the Technolas 217z excimer laser, combines refractive error with corneal architecture, allowing surgeons to approach refractive surgery with a comprehensive analysis of patients' optical systems.

However, Dr. Brint and all other surgeons who performed LASIK in the 1990s had a small subset of patients who developed LASIK-induced spherical aberrations. These patients complained about having difficulties driving at night. In turn, it was those patients who motivated European researchers Theo Seiler, Ph.D., and Michael Mrochen, Ph.D., to look at the original formula used for treatment, the Munnerlyn, and change the algorithm.

"They recognized the fact that the rays from the laser that were ablating the periphery were coming in tangentially and therefore were not delivering the full energy," says Dr. Brint. "To attempt to reduce induced spherical aberration, they added more peripheral pulses."

During this same time period, VISX (AMO/VISX, Santa Ana, Calif.) created its WaveScan Wavefront Analysis System and Alcon (Fort Worth, Texas) created its LADARWave Wavefront Analysis system. These products use the Hartmann-Shack wavefront sensor to further analyze patients' individual eyes. And thus, these two separate developments began the wavefront era.

Similarities and Differences

Surgeons' opinions and preferences also differ on wavefront-guided and wavefront-optimized ablations. Dr. Brint has used both technologies and believes there are some similarities. He says both procedures deliver laser energy in the periphery and are improvements from conventional procedures.

Dr. Milstein, who previously employed wavefront-optimized and now prefers wavefront-guided ablation, agrees. "It's really difficult to tell the difference between the two," he says. "We get great results with the wavefront-guided; we got great results with the wavefront-optimized."

The primary difference in the technologies is that wavefront-guided ablation addresses multiple HOAs, while the wavefront-optimized does not. All surgeons are in agreement about this, and surgeons who prefer wavefront-optimized ablation point to the recent approval of WaveLight's (Erlangen, Germany) Allegretto wavefront-guided technology in the United States.

For his small subset of refractive patients who may require a wavefront-guided ablation — his criteria are 0.4 μm or greater HOAs — Dr. Moore had been advising patients to wait until the FDA approved WaveLight's wavefront-guided software. Sub-sequently, approval was recently obtained. (See page 38.)

Diagnostics

AMO's WaveScan WaveFront System and STAR S4 Excimer Laser System deliver measurement accuracy and treatment precision.

Surgeons who employ both wavefront-guided and wavefront-optimized say almost all patients who come through the door are candidates for either ablation, with the exception of the aforementioned patients with high percentages of HOAs.

In looking at the diagnostic technology associated with wavefront, some physicians point to the development of the aberrometer in recent years as instrumental in determining patients' correction needs.

"You measure the wavefront aberrations of the entire optical system and you are trying to correct that for the individual patient," explains Dr. Brint. "It's truly the most personalized custom treatment that is available."

Tim Peters, M.D., performs preop wavefront measurements on every surgical candidate to determine who may or may not benefit from wavefront-guided ablation. Dr. Peters estimates that 90% of his patients have wavefront-guided procedures these days and the remainder have conventional ablation. He says patient demand for wavefront-guided has been very strong.

"Even those people who are -1 D, with just a little bit of astigmatism, small pupils and not a lot of HOAs to start with, come in and say, 'I want the best,'" explains Dr. Peters.

While Dr. Peters does offer wavefront-guided to most of his patients, he still informs surgical candidates who may only need a smaller correction that they might not get as much value out of it as compared to someone who has HOAs.

Conversely, there may be situations where aberrometers create conflicting data, and surgeons may want to opt for wavefront-optimized or conventional. As aberrometers provide a wavefront-suggested refraction, physicians need to be able to compare that suggested refraction with their own refraction, and sometimes the two do not match.

"If we are just not getting good wavefront data, then we just don't perform it [wavefront-guided ablation]," explains Dr. Peters. He also looks for underlying causes such as dry eye that may create bad readings.

Some surgeons believe the ease of preoperative diagnostic workups associated with wavefront-optimized ablations makes it the more favorable technology. "It's so much simpler," explains Dr. Bond. "It's very reliable and you don't have to use the presurgical aberrometry."

Results

Without the benefit of having long-term large studies comparing the two technologies, there is an absence of empirical evidence to offer insights. However, surgeons report what they are seeing in their own individual practices.

Dr. Whitten reports his enhancement rate with wavefront-optimized is 6% and with wavefront-guided 3%, so wavefront-guided has become his preferred method of ablation. However, Dr. Whitten does say the wavefront-optimized laser is excellent, and he will perform this type of ablation for patients who request it.

Dr. Moore's enhancement rate for wavefront-guided and conventional lasers was 15% and his wavefront-optimized rate is 3%.

Two Lasers, One Practice?

Some surgeons interviewed for this story have both wavefront-guided and wavefront-optimized lasers in their practices. Having multiple lasers may serve as a reflection of the refractive market overall. Surgeons now have a greater number of product choices to serve their patients compared to just a few years ago. And with so much variability in patients' ocular conditions, having the extra technology can help patients and surgeons alike.

For the solo practitioner, however, economics may play a role, and the decision may come down to choosing one laser. In addition, having one laser may improve a surgical team's proficiency. The nuances of performing surgery — even the ergonomics of where a laser sits in relation to patients — are factors surgeons notice.

Dr. Bond believes there is a beneficial effect in working with one laser consistently and that the "choreography" it lends to the surgical team is important.

"LASIK is hugely a team effort and people get used to handing you things in a certain way and having patients in a certain spot; your staff relaxes around them."

As the trend toward integrating several features into one product continues — as witnessed with the latest ophthalmic diagnostic product offerings — surgeons may no longer need to have multiple lasers in their practices. Rather, a single laser with a wider array of capabilities may be suitable to meet the needs of all patients.

It remains to be seen, however, whether manufacturers will develop a one-size-fits-all ablation solution, or if the variability of patients' ocular conditions will continue to keep the refractive market open to several ablation options.