Manufacturers aim to customize corneal ablation to optics of the eye

Issue: June 2000

In an effort to customize refractive surgery for the eyes of each patient, manufacturers are taking conventional topography one step further and developing complex software to help create as precise an ablation pattern as possible.

Autonomous: CustomCornea

Going beyond topography-guided ablation is Summit Autonomous with its CustomCornea technology. CustomCornea uses wavefront sensing to measure the optical aberrations in the eye. In this approach, a small beam of light is directed into the eye and onto the fovea.

A wavefront sensor in the Custom-Cornea measurement device examines the back-scattered light to calculate the aberration profile, said Kevin Liedel, clinical research scientist. “This profile encompasses the entire visual system, not just the corneal surface,” said Dr. Liedel. “The aberration data is then used to determine the precise ablation profile needed for each patient.”

The first treatments using this technology in the United States were performed Oct. 12, 1999, as part of a Food and Drug Administration (FDA) feasibility-phase study. Early results look promising, and the FDA recently granted Summit Autonomous approval to conduct expanded trials at multiple clinical sites, said Dr. Liedel. Commercial approval will likely be some time in 2001, he noted.

Visx: Contoured Ablation Planner

A “topography ablation planner” using proprietary software algorithms is on the front burner for Visx, said marketing manager Thomas McKay. The system, which has been utilized by both Humphrey Systems and Dicon with their topography systems, works in conjunction with a patient’s prescription to tell the practitioner how much tissue should be removed to create theoretically perfect vision for a patient.

“We provide algorithms so the computer in the topography system can actually calculate, if the doctor plugs in the numbers, what the ablation will look like,” he said. “The depth of it, the size of it, where it’s located on the cornea and on the topography map. The doctor can actually simulate a whole series of ablations on an eye that has some sort of irregularity and create a custom ablation pattern.”

Visx is working closely with the FDA for approval for the Contoured Ablation Pattern method for surgery, Mr. McKay said. “It’s very unique,” he stated. “It’s something that we hope doctors can get their hands on sooner rather than later.”

LaserSight: ASTRA

LaserSight Technologies is in the process of launching Advanced Shape Technology with Refractive Algorithms (ASTRA), the umbrella name for all products that will be associated with custom ablation, said Randy Baldwin, marketing manager for laser products.

“Basically, we’re involved right now with developing the ASTRA strategy approach for custom ablation. With the use of corneal diagnostic tools, our software planning package and our laser itself, the LSX, an ablation tailored to the patient will be applied,” he said. “Eventually, we would be using wavefront analysis along with other diagnostic tools to better refine the ablation pattern.”

Mr. Baldwin said that the company has purchased technology and various patents from Premier Lasers to develop the ASTRAMax. This is the company’s refractive workstation that provides diagnostic information for the patient such as wavefront analysis, topography, pupillometry, pachymetry and other important corneal data.

“ASTRA will be targeted toward producing a prolate cornea – the way the cornea is to begin with — as opposed to achieving an oblate cornea, which almost everyone else is doing,” he said. Mr. Baldwin said the system will be unique amidst the competition.

Bausch & Lomb: Zyoptix

Bausch & Lomb Surgical (Claremont, Calif.) has introduced its new Zyoptix technology, which incorporates the Orbscan IIz corneal topographer, the Technolas 217z excimer laser and the Zywave wavefront technology into the system. The Zyoptix system is currently .not approved for use in the United States.

The Zywave, Bausch & Lomb’s wavefront diagnostic device, uses a direct beam of light to capture the way the light reflects off the back of the eye. This system claims to be able to reveal any abnormalities within the entire optical system and to help create a more perfect representation of the eye.

According to Bausch & Lomb, the Zyoptix system will enable surgeons to not only correct refractive conditions, but improve the visual performance of the eye.

Between March 6 and April 5, Jeffery J. Machat, MD, national medical director for TLC The Laser Center, performed 140 surgeries using the Zyoptix technology and found he elicited better qualitative results than when using prior eye measurement devices. He said only a small number of surgeries were performed because it was necessary to collect a large amount of data that must be taken from patients both preoperatively and postoperatively as part of the clinical study of the technology.

The new technology is not without its bugs, however. Dr. Machat said the first several eyes that he operated on resulted in being undercorrected by about 10%, which was basically a result of working with a new technology, he said. Once he corrected for that, the patient who was treated live on satellite resulted in 20/30 5 minutes after surgery and 20/15 by nightfall. Most patients have had an improvement of 1.5 lines, 56% gained best corrected visual acuity (BCVA) of 1 to 3 lines and none lost BCVA of even 1 line.

“The quality is remarkable. Patients having it done have had substantially fewer complaints of glare or halos or no problems at all,” said Dr. Machat , as quoted in Ocular Surgery News (“Zyoptix offers customized LASIK,” May 15, 2000, pp. 36-37).

Unlike most LASIK, which attempts to flatten the cornea, the Zyoptix system allows surgeons to retain the natural curve of the eye by pinpointing certain sections of the eye, which in turn improves the focus of light to the fovea.

For corneal-based irregularities

While topography-based corneal ablation is an effective tool for addressing irregularities in the cornea, it would not be useful in detecting abnormalities in other segments of the eye such as the vitreous, retina or crystalline lens, said Scott MacRae, MD, in group practice at the Casey Eye Institute in Portland, Ore.

“You would have difficulty extrapolating topographic data in people with refractive abnormalities in the vitreous or lens, other than being able to subtract out the topographic astigmatism or abnormality from the refractive abnormality and then surmising there’s another component,” he said. “It’s usually done by induction rather than being able to directly measure it.”

However, wavefront sensing could be used for other irregularities or aberrations not found in the cornea, said Dr. MacRae. And while results for topography-based ablation are fairly accurate, he said, it should not be relied upon solely.

“You’re using a curvature map to determine height,” he said. “There could be a problem in terms of the software, if the curvature map doesn’t translate very well to height mapping. But the preliminary studies have done reasonably well. It’s a bit of an art form; it’s not a simple calculation. It takes some artistic design to do this, and practitioners often do the treatments incrementally. This won’t be as straightforward as, say, treating regular astigmatism. There is more variability with it, but it can reduce irregular astigmatism significantly.”

For Your Information:

Kevin Liedel, OD, MS, is a clinical research scientist for Summit Autonomous Inc. He may be reached at 2501 Discovery Dr., Orlando, FL 32826; (407) 384-1600; fax: (407) 513-7855; e-mail: Kevin.Liedel@autonomous.com.

Thomas McKay is the marketing manager for Visx. He may be reached at 3400 Central Expressway, Santa Clara, CA 95051-0703; (408) 733-2020; fax: (408) 730-1399.

Randy Baldwin is the marketing manager for laser products for LaserSight Technologies Inc., 3300 University Blvd., Suite 140, Winter Park, FL 32792; (407) 678-9900; fax: (407) 678-9981; Web site: www.lase.com.

Jeffery J. Machat, MD, can be reached at TLC Laser Eye Centers, 4101 Yonge St., Ste. 100, Toronto, Ontario, M2P 1N6, Canada; (416) 733-2020; fax: (416) 733-0316. Dr. Machat has no direct financial interest in any of the products mentioned in this article. He is a paid consultant for Bausch & Lomb.

Bausch & Lomb Surgical may be contacted at 555 W. Arrow Hwy., Claremont, CA 91711; (800) 423-1871; fax: (909) 399-1525.

Scott MacRae, MD, is in group practice at the Casey Eye Institute, a university-based program at Oregon Health Science University. He may be reached at 3375 Southwest Terwilliger Blvd., Portland, OR 97201. Dr. MacRae has no direct financial interest in any of the products mentioned in this article, nor is he a paid consultant for any companies mentioned.