BBI Contributing Editor

Excimer laser manufacturers are on a fast track to provide wavefront technology or comparable innovations for custom corneal ablation. Each company is developing a unique approach, and first-generation devices already are entering the market. However, potential customers are understandably somewhat confused by the technical variations of these complex optical systems.

The WaveScan Wavefront system by Visx (Santa Clara, California) is based on Hartmann-Shack principles and was developed by 20/10 Perfect Vision (Heidelberg, Germany). Already FDA-approved as a diagnostic system, the device sells for $75,000 and should be available for custom ablations internationally by this spring. U.S. clinical trials also are scheduled to begin around that time.

According to Stephen Trokel, MD, a professor of clinical ophthalmology at Columbia University (New York), the WaveScan Wavefront system has successfully treated patients who have previously undergone refractive surgery but have been left with reduced visual acuity and ghost images "because of some mixed irregular astigmatism induced by the first surgical procedure." Upon retreatment, patients achieved asymptomatic 20/15 vision.

Visx also has developed a unique patient screening protocol whereby a test optical lens is first cut and placed in front of the eye to ensure that there will be an improvement in visual acuity. "Personally, as a professor of ophthalmology, I think patients who have had a less than perfect refractive surgery result should take priority over those patients who are already seeing 20/20 and want to achieve 20/10," said Trokel, a consultant with Visx. Overall, the challenge "will be how to select the best aberrations for the healthiest vision."

Last October, Tracey Technologies (Houston, Texas) entered into a letter of intent with TLC Laser Centers (Mississauga, Ontario) to develop and use the Tracey Visual Function Analyzer. Unlike the Hartmann-Shack principle, "our system is based on ray tracing or what is called the thin-beam principle," said Joe Wakil, MD, Tracey's chairman and CEO. "A thin beam of light is traced through the optical system of the eye. We then precisely determine where that beam strikes on the retina. This results in a single point of measurement."

A rapid series of parallel beams is measured in likewise fashion within milliseconds. "This sequential measurement of points within the entrance pupil avoids any data confusion," Wakil said. In contrast, simultaneous measurement of multiple points in a highly irregular eye "may lead to data confusion and erroneous measurements."

Clinical trials to date indicate "excellent reproducibility, incredible speed within 15 milliseconds and software-driven versatility," he said. "Currently, we are working on improving accuracy and range of the device."

The Tracey Visual Function Analyzer is expected to become commercially available soon. Price has yet to be set.

WaveFront Sciences (Albuquerque, New Mexico) formed a partnership with Asclepion-Meditec last August to co-market a Hartmann-Shack wavefront analyzer called COAS (complete ophthalmic abberometer system). "Our company is the largest manufacturer of Hartmann-Shack sensors in the world," said Daniel Neal, PhD, cofounder, vice president and technical director at WaveFront Sciences. "Our whole technology is based on high-quality micro-optics," Neal said. "These are made the same way as you make a computer chip. The resolution and precision of the lenslet array determines the accuracy of the entire system."

For ophthalmic applications, COAS can measure "down to 100ths of a diopter but also measure a very large range of diopters, compared to lower-resolution devices that sacrifice either accuracy or dynamic range," Neal said. Scientific studies "confirm our expectation that we can make very accurate measurements." The company's first production run of COAS was purchased entirely by Asclepion-Meditec. The selling price is $76,000.

The CustomCornea wavefront system from Alcon Summit Autonomous (Fort Worth, Texas) also is based on the Hartmann-Shack principle and is being developed in conjunction with Zeiss Humphrey (Dublin, California). "Our very initial clinical trial results, starting from October 1999, were essentially equivalent to our conventional surgery," said George Petit, MD, PhD, chief scientist at Alcon Summit Autonomous. "But over the last year, we've learned a lot about how we translate the wavefront data into the best ablation profile." The latest LASIK results are "very preliminary, but we do believe we are seeing a benefit in the customized approach," Petit said. The CustomCornea system should be commercially available this spring. "We have a very large dynamic range. We have measured patients that are very high myopes, very high hyperopes, and patients that have been diagnosed with keratoconus [a cone-shaped deformity of the cornea]. So we believe we have a very robust measurement technology," Petit noted.

CustomCornea is also largely automatic. "The operator simply has to line the eye up," Petit said. "After determining the patient's refractive error, we make the target slightly blurry, which encourages the eye to be in the most relaxed state." Repeat measurements for consistency are performed rapidly as well.

Nidek (Fremont, California) expects U.S. approval of its OPD (optical path difference)-Scan refractive power/corneal analyzer early this year. "We don't use the Hartmann-Shack principle," said Ray Sayano, PhD, general manager at Nidek Technologies in Pasadena, California. Instead, the company uses a system based on retinoscopy.

This stand-alone unit, which will sell for $35,000, "measures well over 1,400 data points, compared to less than 100 data points with Hartmann-Shack wavefront analysis," Sayano said. Consequently, "our system offers better resolution for the detection of higher orders of aberration." In addition, "we can simultaneously perform corneal topography and power mapping of the cornea. Other companies simply offer a wavefront unit; then you need to purchase a separate topographic unit." Furthermore, there may be problems operating the two units side by side. "By using two different pieces of equipment, you may not be looking at the same axis," Sayano noted.

WaveLight Laser Technologie AG (Erlangen, Germany) is developing wavefront technology for Coherent Medical Group (Santa Clara, California). The two companies also have an international distribution agreement for the WaveLight WaveFront Analyzer, currently being used at European clinical sites. However, U.S. and Japan distribution are currently unassigned and are excluded from the agreement. Nonetheless, the competitively priced device should be available in the U.S. early this year.

The WaveLight Analyzer is not based on the Hartmann-Shack principle of wavefront aberrometry, "but rather the other major form of performing wavefront analysis, which is the Pscherning," explained Peter Falzon, director of marketing for ophthalmology at Coherent. "The principle is to send a grid of lights through the pupil imaged onto the retina and then measure the actual location of each point of light on that grid at the retinal surface and compare it to the standard, which would be for perfect vision. You're actually involving a wider range of the cornea, rather than just the central part of the cornea as with the Hartmann-Shack principle." For measuring higher-order aberrations, "which tend to occur farther out from the center of the cornea, we believe our system will provide more information because we are involving more of the cornea," Falzon said. "We're also measuring that grid on the retina, rather than a reflection of that grid back outside the eye."

Randy Mansfield, director of refractive marketing for the Americas at Bausch & Lomb (Claremont, California), is enthusiastic about his company's Zywave Hartmann-Shack aberrometer. However, "we do not believe that customized ablation is aberrometer-driven ablation. Rather, we believe you need to include the Orbscan [a multi-dimensional, 3-D corneal-measurement device]," Mansfield said. "An aberrometer can provide you with a layout of the eye and tell you where the aberrations are, but it cannot tell you where those aberrations originate from. Therefore, true customized ablation requires integrating an aberrometer with the Orbscan data to provide the recommended shot profile for the laser."

FDA clearance for the Zywave is expected sometime in 2001. In the meantime, this system (priced at approximately $40,000) is being marketed internationally.

LaserSight Technologies (Winter Park, Florida) anticipates international launch of its CustomEyes system this spring. Official clinical trials are scheduled to begin January at three or four international sites. The company hopes that practitioners will embrace its new line of ASTRA (advanced shape technology refractive algorithm) products to achieve customized ablations. Included in the $50,000 CustomEyes system are ASTRAMax, a diagnostic device, and ASTRAPro, the computer software for a surgeon to plan the ablation.

"We have developed proprietary software with the goal of reducing spherical aberrations and higher-order aberrations, which will reduce or eliminate the wavefront error," said David Neisler, vice president of marketing at LaserSight Technologies. "Through our research, we found that this method does not require the use of a wavefront device to actually drive the process." Although clinical trials "will use a Hartmann-Shack wavefront device to measure the optical corrections, we will not incorporate the wavefront data to plan the ablation," Neisler said.