EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
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82 EW FEATURE February 2011 Refractive March 2012 Custom LASIK by Jena Passut EyeWorld Staff Writer AT A GLANCE • Wavefront-guided and topography- guided, both used to reshape the cornea, are two very different LASIK platforms • Topography-guided LASIK, which is not yet available in the U.S., is used to treat patients with highly irregular corneas • Wavefront-guided LASIK has been shown in several studies to be highly effective for regular corneas Wavefronts are all the rage, so where will topography- guided systems fit in? F or refractive surgeons, custom LASIK platforms are producing amazing results for patients with tradi- tional spherical refractive error. So where will extremely cus- tomizable topography-guided plat- forms, which aren't yet available in the U.S., fit in? Topography-guided platforms are used to treat patients with irregular corneas. "That's really where you need the fingerprint identification of the cornea and to be able to treat every cornea for those specific defects," said David Goldman, M.D., assis- tant professor of clinical ophthal- mology, cornea and external disease department, Bascom Palmer Eye Institute, University of Miami Miller School of Medicine. A recent report in the Journal of Cataract & Refractive Surgery reported that topography-guided LASIK re- sults were excellent in patients who had a decentered ablation. "It's a great technology that's going to apply, I think, to a small percentage of patients, and those are the people who have some irregularity of the cornea where it's so critical to measure the corneal topography and treat it specifically," Dr. Goldman said. Wavefront-guided Wavefront-guided systems create a customized ablation profile by using three-dimensional measurements of the patient's cornea. The wavefront This graphic shows the drop in enhancements once Dr. Probst started using the CustomVue. It went from around 6% to 2 or 1.5% Source: Louis E. Probst, M.D. map is then used to guide the laser to reshape the corneal surface and correct any abnormalities. Currently, there are two types of wavefront platforms. A wave of light is used in wavefront-guided plat- forms to measure the cornea's opti- cal abnormalities, while the laser corrects those aberrations and the treatment prevents the onset of further ones. Abbott Medical Optics (AMO, Santa Ana, Calif.) offers the iLASIK and VISX CustomVue platforms, while Alcon (Fort Worth, Texas) owns the Wavelight Allegretto Wave, and Bausch + Lomb (Rochester, N.Y.) offers the Zyoptix. For Louis E. Probst, M.D., national medical director, TLC Laser Eye Centers, who uses the CustomVue and VISX systems, the results of custom LASIK have been nothing short of "mind blowing." "It's no question, for the stan- dard patient, wavefront-guided is ex- traordinarily effective, particularly used in conjunction with IntraLase [AMO]," he said, adding that he gets "ridiculously incredible" results, such as 98% of patients seeing 20/16 or better uncorrected post-op, 78 are 20/12, and 50% are 20/10. Those are patients who went into the procedure with healthy corneas, however. "For problem patients, particu- larly those with keratoconus or ecta- sia, topography-guided treatment makes more sense," Dr. Probst said. The technology, however excel- lent, is not without risks. "Custom-guided ablations do tend to take a little more tissue than your regular ablation profiles, so if you are doing a really high treat- ment or have a patient with a cornea on the thin side, you have to be a little more cognizant of that," Dr. Goldman said. "You need to be aware of how much tissue you are taking or leaving the patient with for the residual stromal thickness." One of the issues with the meas- urement is that it is static, while wavefronts generally are dynamic, said A. John Kanellopoulos, M.D., associate clinical professor of oph- thalmology, New York University, New York, and director of laser vi- sion, GR Institute, Athens, Greece. "It is very difficult to make a conclusion that this measurement is the optimal wavefront of this pa- tient and if I mimic the changes that the wavefront imaging determines, then I will have an optimal wave- front environment for the patient," he said. Topography-guided Topography, on the other hand, is highly reproducible and can give a surgeon correction at the level he or she desires. "One of the differences when you treat irregularities, where you need a customized treatment, how- ever, is that topography-guided does not have the brain cells, so to speak, to correct refraction," he said. "The topography-guided system will give you a much better optical media as far as regularity and the IHD index of height decentration and IHA index of height asymmetry." Dr. Kanellopolous said clinicians in Europe also see the value in using topography-guided LASIK as a hyperopic treatment up to +0.6 D. "By definition topography- guided treats on the visual axis, not on the geometric center," he ex- plained. "In my mind, hyperopic LASIK should only be topography- guided LASIK because it treats on the visual axis versus the center of the cornea. If you treat a hyperopic eye as the opposite of myopia, you're invariably misplacing the ablation temporally." Surgeons in Greece also have incorporated corneal collagen crosslinking into this hyperopic treatment, which may change the thinking that hyperopia "is something that regresses," Dr. Kanellopolous said. Just comparing imaging alone in irregular corneas, Dr. Kanellopolous said topography sys- tems are superior because "it's ex- tremely rare that you are not able to obtain reproducible maps with to- pography, whereas wavefront imag- ing of these corneas is very challenging." Limitations Still, each system has its limits. "Topography-guided is limited as being able to have a good picture of what the spherical equivalent of that eye would be after the procedure," Dr. Kanellopolous said. As with any surgical procedure, there are risks. "When you increase the index of irregularity and incor- porate it into treatment, you're be- coming extremely demanding of the centration and reproducibility of that treatment," Dr. Kanellopolous said. "You increase the gains, but you quadruple the risks. Say I envi- sion an irregularity that is a map of Greece, for instance, and I ablate that irregularity of Italy, then I exac- erbate that irregularity by three times." The difficulty is exacerbated be- cause most images of patients' eyes