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Wavefront-guided ablation: promising, but not universally accepted
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Although wavefront-guided custom ablation has emerged as the most promising technology for correcting a variety of visual aberrations, it has not been unreservedly embraced by all practitioners.
“It’s still a new technology,” said John W. Potter, OD, FAAO, vice president of clinical services for TLC Laser Eye Centers. “We are learning more about it every day.”
How often is wavefront used?
The frequency with which wavefront is used varies from practitioner to practitioner. Dr. Potter told Primary Care Optometry News that between 85% and 90% of patients falling within current FDA approval ranges are treated with wavefront at TLC centers. “The parameters are such that we can’t treat all patients with custom,” he said.
Marc R. Bloomenstein, OD, FAAO, said his center treats about 45% of patients with wavefront. “We are definitely seeing better visual acuity and more immediate results with our custom patients,” said Dr. Bloomenstein, who is refractive clinic medical director at Barnet Dulaney Perkins Eye Center, Phoenix.
Andrew L. Moyes, MD, of Moyes Eye Center in Kansas City, said between 5% and 10% of his refractive surgery procedures are wavefront-guided. “My laser does really well with standard ablation. Frankly, wavefront is only a small improvement over standard,” he said in an interview. “The reasons for this low percentage are that patients need to come back for a second day of testing, and other costs are involved.”
Problematic higher-order aberrations
One of the most significant benefits of wavefront analysis is its ability to detect and treat higher-order aberrations.
“We select people for wavefront based upon their higher-order aberrations,” Dr. Moyes told Primary Care Optometry News. “If patients have an RMS higher than 40 µm ... we would consider them for wavefront.”
Dr. Moyes said the most problematic higher-order aberrations are trefoil and spherical aberration because of their visual significance. “Those are aberrations that cause problems if they are not treated or if they are induced by the original ablation,” he said.
Dr. Bloomenstein said, in many ways, spherical aberration is the most problematic. “Spherical aberration has been shown to be a reason or a precursor for glare or halo,” he said. “So, if it is established that a patient has a significant amount of spherical aberration, it would be extremely beneficial to use wavefront technology to reduce the bad aberrations.”
Dr. Bloomenstein added that coma and trefoil are among the most recalcitrant aberrations. “Coma and trefoil seem to be a little bit more challenging when it comes to eradicating or reducing the amount of aberrations,” he said.
In any case, Dr. Potter said, wavefront has been shown to leave patients with fewer induced higher-order aberrations than does standard refractive surgery. “It’s not what you start with; it’s what you end up with,” he said. “With custom LASIK, you end up with fewer higher-order aberrations than with conventional, regardless of where you start.”
Some of wavefront’s most significant benefits to visual performance tend to manifest themselves in the area of enhanced mesopic and scotopic visual function. “One of the most important parts of doing a wavefront-guided ablation is looking for mesopic or scotopic visual improvement,” Dr. Potter said. “That is a significant benefit.”
Resistance to wavefront
Dr. Potter said successful use of wavefront technology requires a basic knowledge of visual science. “To be successful with custom LASIK, you must have a reasonable understanding of vision science,” he said. “Optometrists get 4 semesters of vision sciences in optometry school, where ophthalmologists get no academic vision science training at all.”
This training, Dr. Potter said, has proven to be useful to optometrists in understanding and embracing wavefront refraction. “If you asked most optometrists when they were in school whether they believed those four semesters would be useful to them, they probably would have said no,” he said. “But it turns out that they are very useful in today’s refractive surgery.”
Ophthalmologists, on the other hand, may have a lesser understanding of vision science, Dr. Potter said. “They won’t ever say that they don’t know it,” he said. “The manufacturers don’t know that the surgeons don’t know it. Then they wonder why surgeons aren’t doing more custom.”
Dr. Potter said wavefront can be difficult to understand, and without the basic vision science training, it can be even more difficult. “Additionally, the actual wavefront analysis procedure can be challenging,” he said. “If practitioners don’t get great results when they first start, they might have a tendency to become frustrated and go back to conventional LASIK.”
Dr. Potter pointed out that wavefront-guided LASIK, in addition to being more precise in correcting higher-order aberrations, is also ultimately safer. “It’s safer because you end up doing fewer enhancements,” he said. “We are always trying to make it safer and better for patients. Also, because it leaves patients with fewer induced higher-order aberrations, they see better at night and their visual acuity is sharper.”
Return to surface ablation?
Surface ablation (either photorefractive keratectomy or laser epithelial keratomileusis) is a viable alternative to LASIK for some patients, particularly for those patients whose corneas are too thin or flat for LASIK.
“We do about 10% surface ablation,” Dr. Moyes said. “Frankly, one of the reasons we do surface ablation is safety. If we feel the patient has a borderline amount of thickness, we would consider surface ablation.”
Surface ablation would also be an option if some sort of abnormality is spotted on the initial diagnostic tests, Dr. Moyes said. “If we see something on the Orbscan [Bausch & Lomb, Rochester, N.Y.], such as a posterior surface that looks a little funny, it could be a very early type of keratoconus. While it is not significant enough for us to cancel the case, we would do surface ablation for safety,” he said.
This type of ablation could also be useful for those entering the armed forces, Dr. Moyes added. “These patients may feel that surface ablation is desired or required either by the armed services or by their occupation,” he said.
But Dr. Moyes does not feel at this time that surface ablation could surpass LASIK at the forefront of refractive surgery. “As I read the literature on LASIK inducing higher-order aberrations, it is such a small order of magnitude that I don’t feel surface ablation would provide a significant advantage,” he said.
For Your Information:
- John W. Potter, OD, FAAO, is a Primary Care Optometry News Editorial Board member and vice president of clinical services for TLC Laser Eye Centers. He can be reached at 18352 Dallas Pkwy., Suite 136, Dallas, TX 75287; (972) 818-1239; fax: (972) 818-1240; e-mail: john.potter@tlcvision.com.
- Marc R. Bloomenstein, OD, FAAO, is a Primary Care Optometry News Editorial Board member and refractive clinic medical director at Barnet Dulaney Perkins Eye Center. He can be reached at 4800 N. 22nd St., Phoenix, AZ 85016; (602) 955-1000; fax: (602) 508-4744; e-mail: Mbloomenstein@BDPEC.com.
- Andrew L. Moyes, MD, practices at Moyes Eye Center in Kansas City, Mo. He can be reached at 5844 N.W. Barry Rd., Ste. 200, Kansas City, MO 64118; (816) 455-2020; fax: (816) 587-3355.