Excimer Lasers: Today's State of the Art

Recent technology improvements give surgeons greater precision and patients better outcomes.

BY ROCHELLE NATALONI

With 16.3 million patients having had LASIK worldwide, and more than a decade of clinical study and technological innovation behind it, LASIK is considered among the most successful elective procedures available today, according to a literature analysis led by Kerry Solomon, M.D. at the Storm Eye Institute of the Medical Center of South Carolina. The primary goal of this literature review, which found that an average of 95.4% of LASIK patients are satisfied with their results, was to gauge LASIK patient satisfaction for a task force formed by the U.S. Food and Drug Administration (FDA) and comprising the American Society of Cataract and Refractive Surgery (ASCRS), the American Academy of Ophthalmology (AAO), and the National Eye Institute (NEI), among others.

Laser vision correction with today's excimer laser systems bears little resemblance to the rudimentary ‘flap and zap’ procedure of the early 1990s, and the exceedingly high and recently documented level of patient satisfaction is due in no small part to the safety and efficacy of the equipment with which LASIK and related refractive laser procedures are performed. Whether they provide wavefront-guided, wavefront-optimized or topography-guided ablations, these systems — the AMO VISX STAR S4 IR, Carl Zeiss Meditec MEL 80, Bausch & Lomb Zyoptix, Alcon WaveLight Allegretto Wave and Nidek EC-5000 — provide greater precision and predictability than ever before. The capabilities of the newest incarnation of each of these systems are reviewed in this article.

Bausch & Lomb Zyoptix

The Zyoptix laser vision correction system from Bausch & Lomb offers both anatomical and optical customization, according to Scott MacRae, M.D., Professor of Ophthalmology at the University of Rochester School of Medicine, one of the device's clinical investigators. "Not only does it offer advanced wavefront-guided ablation, which accounts for the preoperative manifest refraction and aberration interaction, but the myopia correction is customized to each patient's higher-order aberration (HOA) profile and an optical zone that can be customized for each patient," says Dr. MacRae. Additionally, he points out, the platform is proven to consistently reduce higher-order aberrations, particularly the third order aberrations coma and trefoil, which are the most prevalent type of aberration in the general population.

Among the key patient benefits offered by Zyoptix, according to B&L, is significantly improved night-driving ability compared to that of patients undergoing conventional non-customized treatment, with greater than 40% of patients noting improved night vision. This is especially important in light of the results of a recent national survey by Road & Travel magazine, which showed that nearly one-third of LASIK-aged drivers wearing glasses or contacts have significant difficulty driving at night, according to Bob Anello, director of B&L's Refractive Marketing group. "In the Zyoptix FDA study, patients were four times more likely to note improvement in night driving compared to patients whose night driving worsened," says Dr. MacRae, "but none of the 190 patients studied were dissatisfied with the procedure," he adds.

Figure 1. The Zyoptix from Bausch & Lomb.

Dr. MacRae points out that the effects of myopia/HOA coupling can reduce the predictability of wavefront-guided treatments and lead to over- or under corrections, and that Zyoptix adjusts for this coupling when calculating the sphere correction. "With Zyoptix, each eye has a unique nomogram adjustment that accounts for aberration interaction, thereby virtually eliminating over-corrections," says Dr. MacRae. "My personal results using this approach are that 95% of eyes achieve 20/20 or better uncorrected and 96% are within 0.5 D of target," he adds.

The Zyoptix Advanced Personalized Technologies upgrade includes the Advanced (or Rochester) Nomogram, a 100 Hz laser upgrade and a low mesopic pupil extrapolation program, and no longer requires pharmaceutical dilation for an aberrometry exam. "The Zywave aberrometer now measures low mesopic pupil size. I much prefer non-pharmacologic dilated Zyoptix in most cases with low mesopic pupils 5.4 mm or larger, which is 80% of the time," says Dr. MacRae. "With the latest expanded sphere treatment offset, I can now use the Zyoptix Advanced Nomogram in all custom cases, as well as in monovision cases," he adds. Dr. MacRae's retreatment rate has been cut in half through the use of the University of Rochester Advanced Treatment Nomogram.

Hyperopia correction and the next generation of iris registration (IR) eye tracker are both expected for Zyoptix in the U.S. in the first half of next year, according to Anello. The IR tracker will provide pupil-shift compensation and cyclotorsion adjustment, as well as real time rotational adjustment throughout the ablation. This provides further rotational accuracy when treating non-rotationally symmetric aberrations such as astigmatism, coma and trefoil (common in the population), thus astigmatism and higher order aberrations are more accurately treated, according to Dr. MacRae.

Alcon's WaveLight Allegretto Wave Eye-Q

Alcon's WaveLight Allegretto Wave systems provide the option of either standard LASIK, which it markets as wavefront-optimized treatment, or custom LASIK, which is known as wavefront-guided treatment. Depending on which WaveLight model — 200 Hz or 400 Hz — is used, it only takes 2 or 4 seconds (respectively) for the removal of 1 diopter at a fully corrected optical zone of 6.5mm, according to Karl G. Stonecipher, M.D., medical director of TLC, Greensboro, N.C. To ensure safety and precision at such high speeds, the system's PerfectPulse Technology controls each laser pulse from its generation to the point when it contacts the cornea, Dr. Stonecipher explains.

Dr. Stonecipher has been working with the Allegretto Systems since 2000. "The latest iteration of this system has allowed us to perform the procedure faster with better throughput. The flap is back for less time; there's less exposure, so there's less drying," says Dr. Stonecipher. "In terms of outcomes, both the wavefront-optimized and the wavefront-guided platforms have done extremely well."

Figure 2. The Allegretto Wave Eye Q from Alcon.

Up to 99% of patients with up to -7 D of myopia and up to 3 D of astigmatism treated with WaveLight's wavefront-optimized platform achieved 20/20 or better, with gains in lines of vision from 30% to 35%, according to Dr. Stoncecipher, who also says that 92% to 93% of patients with -7 D to -11 D of myopia and up to 3 D of cylinder achieved 20/20 vision. "We are seeing excellent results, and that's with no enhancement," said Dr. Stonecipher. "The enhancement rate for the average WaveLight user will be in the 1% to 2% percent or less range for the average population," he adds.

Zeiss Meditec MEL 80

The Carl Zeiss Meditec MEL 80 maintains a place among the leading excimer lasers because of its outstanding clinical outcomes, proponents say. According to its FDA clinical data, 93% of patients had an uncorrected visual acuity of 20/20 or better 6 months postoperatively. What's more, the study found that more than 40% had an uncorrected visual acuity of 20/12.5 or better.

Figure 3. The MEL80 from Carl Zeiss Meditec.

The MEL 80 is fast, with a speed of 250 Hz, yet it avoids corneal thermal stress, according to James Carter, vice president ophthalmic surgical sales at Carl Zeiss Meditec. "This system is able to resolve a diopter of myopia in 3 seconds and seven diopters of myopia in about 22 seconds," he points out. The MEL 80 has a Gaussian beam profile with a very small spot size (0.7mm), which allows for rapid visual recovery and consistent, safe results, according to Carter. "The thermally optimized firing pattern protects the stroma, minimizing the surface heating effects, which results in rapid visual recovery," he said. The system is portable and is relatively simple to operate, says Carter, who adds that this feature enhances high-volume office workflow.

The FDA has approved the MEL 80 for use on patients with up to 7 D of myopia and 3 D of astigmatism, and Zeiss is expecting FDA approval for hyperopia, expanded range myopia, and mixed astigmatism in the near future, according to Carter. For the high myopia study, subjects were treated with sphere and MRSE up to -12 D. FDA approval will be dependent upon review of the data gathered from these high myopia subjects.

"In late December 2007, Carl Zeiss Meditec filed a PMA supplement with the FDA for the treatment of hyperopia," says Carter. "The FDA is in the process of reviewing that submission and approval is anticipated late in 2008," he adds. CZM is also conducting studies of high myopia and mixed astigmatism under an investigational device exemption. Subject enrollment is completed for the high myopia study and nearing completion for mixed astigmatism. Submission of these two studies to the FDA is anticipated in 2009.

AMO/VISX Star S4 IR

AMO has combined its STAR S4 IR laser system with WaveScan treatment planning and IntraLase flap technology, and is celebrating the union with an inspired branding strategy: iLASIK, which AMO says calls to mind all things high-tech and drives demand for the procedure among today's youth, who respond to the popular "i" designation.

"We've conducted numerous clinical trials using the VISX platform for more than 10 years, and our patients have enjoyed significant improvements in visual acuity and quality of vision due to advances in the platform" says David J. Tanzer, M.D., Surgical Director, Refractive Surgery Center, Department of Ophthalmology, Naval Medical Center, San Diego.

Dr. Tanzer bases his observations of the STAR S4 IR on his use of the system in his practice, as well as on his experience as a clinical investigator. "The current platform has several components — WaveScan technology with Variable Spot Scanning/Variable Repetition Rate, Iris Registration and Advanced CustomVue software, which uses 100% of available Hartmann-Shack data points — that work together to provide the uncompromising outcomes that we are experiencing," he says.

Figure 4. AMO/VISX's Star S4 IR.

"The laser's iris-mapping feature, known as Iris Registration, facilitates exquisite centration and orientation of the ablation pattern to the cornea," says Dr. Tanzer, "and as the laser is working to precisely remove corneal tissue, it does so using sophisticated algorithms, known as Variable Spot Scanning and Variable Repetition Rate, which minimizes the amount of tissue that is removed, speeds up the treatment and keeps the cornea as cool as possible during the ablation," he says.

The STAR's customized ablation profile can be further refined for the individual patient's needs by employing a physician adjustment, which Dr. Tanzer says allows the surgeon to offset the spherical component of the treatment to further tailor the outcome. "For example, when we treat a young Navy pilot, we tend to target +0.25 to +0.50 as a final refractive outcome to ensure excellent uncorrected visual acuity in all environmental conditions, including high-performance aircraft at night," he said.

The most recent study using the STAR S4 IR laser platform resulted in uncorrected visual acuity of 20/20 or better in all patients 2 weeks postoperatively, according to Dr. Tanzer. No subjects in the study, which is close to 1 year out, have required retreatment. The range of spherical equivalent in this study ranged from +3 D to -6 D. "By 1 month, 64% of subjects gained [1 or more] lines of best corrected visual acuity, and 88% of eyes uncorrected postoperatively were as good as or better than they were best corrected preoperatively," he says

Dr. Tanzer participated in a clinical study comparing the STAR IntraLase flap technology to two different mechanical microkeratomes. "All the clinical parameters that were measured favored the femtosecond laser," says Dr. Tanzer. "The flaps are more structurally intact due to the side-cut architecture, and they induce less dry eye," he says.

Nidek EC-5000

Nidek's EC-5000 is an example of an excimer laser that provides smooth delivery of scanning slit laser energy. Nidek's beam control technology reduces the need for frequent maintenance and complicated optical adjustments, according to refractive marketing manager Frank Wood. Combined with computer-based innovations, the EC-5000 ensures optimal blending of the ablated and non-ablated areas, producing a smooth transition zone while virtually eliminating central islands on the cornea, he says. Other benefits include user-friendly software and display screens that provide comprehensive information during every procedure, and an optional hands-free eye tracker for added surgeon convenience, Wood says.

Figure 5. Nidek's EC-5000.

At press time, Nidek's Customized Aspheric Treatment zone (CATz) software for topography-guided treatment with the EC-5000 laser was pending FDA approval. The three benefits to Nidek's excimer laser with CATz are better results for night driving (in comparison to EC-5000 without CATz), more data points and no per-procedure fees, according to Wood. OM