As you are likely well aware, wavefront measurement and custom ablation are the hottest topics in the laser refractive industry right now. Laser manufacturers and diagnostic companies are racing to position themselves to introduce the next big thing in laser vision correction.

The marketing of this technology to patients is assumed to be a slam-dunk. After all, who wouldn't rather have an ablation pattern developed specifically for his eye? But with all the talk and excitement swirling around this topic, it can be difficult to discern what's actually going on.

Read on for an explanation of where our industry is with wavefront technology and custom ablation, and what needs to happen for the promise of these technologies to be fully realized for surgeons and their patients.

How this race began

The idea of a customized ablation pattern has been around since the development of the excimer laser. Some of the initial lasers had corneal topographers built into the design under the assumption that laser ablation would be controlled in real time.

However, development teams quickly realized that real-time corneal topography-controlled ablation was problematic. Nevertheless, isolated studies continued with a focus on treatment of asymmetric astigmatism and other corneal irregularities that couldn't be addressed with standard ablation patterns.

Patients with asymmetrical corneas actually make up a small segment of the population, but they often have severe vision problems, some of which are surgically induced. Techniques have been developed to address these problems with solutions such as the VISX Contoured Ablation Pattern (CAP) Method, which allows the surgeon some direct control over the location, size and depth of the laser ablation. Other lasers offer similar features, and many companies are still studying corneal topography-controlled ablation.

As scientists and clinicians struggled with the shortcomings of topography-controlled ablation, the concept of wavefront analysis emerged, and the objective changed from the correction of asymmetrical corneas to customizing all ablation patterns. This offered the prospect of eliminating all optical aberrations, thereby targeting perfect vision.

Unanswered questions

Behind the marketing hype, however, is a serious debate over the merits of removing all optical aberrations. Issues include how vision quality should be measured and qualified, the effects of optical aberrations and patients' neural ability to benefit from their elimination. Also key to this debate is the lack of understanding of age-related changes to the natural lens and what impact this has on optical aberrations.

In February, the First International Congress of Wavefront Sensing and Aberration-Free Refractive Correction was held in Santa Fe, N.M. The 1-day conference focused on the scientific principles behind this technology and different measurement techniques. (The conference was recorded and is available over the Internet at www.specialtymd.com.)

Five methods of measuring higher-order optical aberrations were identified at the meeting:

�        Hartmann-Shack aberrometry

�        spatially resolved refractometery

�        Tscherning aberrometry

�        ray tracing aberrometry

�        scanning slit refractometery.

In an effort to move forward with the technology, manufacturers have selected different measurement methods to develop. As with any new technology, the first manufacturer to make it into the marketplace has many advantages, which include establishing standards that influence all products to follow. However, a lack of consensus on underlying scientific methods and measures complicates the development process.

The ultimate success of these various development programs may be determined not only by the efficiency and effectiveness of the laser in creating a custom ablation, but also by the time it takes to gain market approval and acceptance of the measurement methods and techniques.

Who's doing what

This race to the market has led to the decoupling of wavefront measurement technology and laser platform, as manufacturers feel pressure to begin development or fall behind.

Diagnostic devices require limited regulatory review. So the time to market can be measured in months as compared with years for completion of FDA clinical trials of a laser to perform custom ablations. Introduction of a successful wavefront diagnostic instrument will pave the way for a combined diagnostic instrument and laser.

At least seven entities are currently developing wavefront technology: Summit Autonomous, VISX, Bausch & Lomb, the University of Dresden, Nidek, LaserSight and Tracey Technologies. A summary of their efforts follows.

�        Summit Autonomous. Summit Autonomous originally developed its wavefront measuring technology as a component of the LADARVision laser system and only recently decided to sell the unit as a stand-alone device. The Custom Cornea Accessory Device (CCAD) relies on Hartmann-Shack aberrometry, deformable mirrors and a CCD array to produce a three-dimensional map of the refractive power of the eye. Humphrey Instruments will manufacture the freestanding diagnostic instrument.
Summit Autonomous began FDA clinical studies for custom ablation using the combination of CCAD and the LADARVision laser last fall. The company recently received FDA approval to expand those studies to an additional 100 eyes and hopes to use data from those patients to move into a Phase III-type study on several hundred eyes. Assuming that progress stays on course, a full FDA approval by the end of 2001 is within the realm of possibility.

�        VISX. The VISX answer to wavefront analysis was announced last year at the American Academy of Ophthalmology (AAO) meeting in Orlando. The WaveScan Wavefront Analysis System is also based on Hartmann-Shack aberrometry, but it uses a custom-designed microchip to serve as the deformable mirrors. Unlike the Summit CCAD device, the unit was designed first and foremost as a diagnostic instrument. It produces refractive maps similar to the familiar corneal topography maps. The first shipments of the device are scheduled this fall, in time for the AAO meeting.
The first step for VISX toward a combination wavefront-custom cornea solution, a three-dimensional active eye tracker, was announced in late April along with the introduction of the Star S3 laser. While it's limited now to pausing the laser during periods of large eye movement, the enhancement lays the groundwork for future integration with the WaveScan and Star S3 to produce a custom ablation. U.S. clinical trials with the new device hadn't begun at press time.

�        Bausch & Lomb. The goal for B&L's Zyoptix system, which was introduced during a recent satellite/Internet broadcast event, is to combine the capabilities of the Orbscan II mapping device with the company's wavefront instrument, called Zywave, and the Technolas 217 laser. Zywave uses a combination of ray tracing aberrometry and ultrasound corneal topography to measure the wavefront.
International clinical trials are under way with availability in those markets expected as early as this month. U.S. clinical trials hadn't begun at press time.

�        University of Dresden. This German University has developed the Wavefront Analyzer, which utilizes Tscherning aberrometry and corneal topography to create an ablation profile that can be used to control the excimer laser. The device projects a 13 T 13 spot array onto the retina and then captures the image with a CCD camera. The resulting image is analyzed and compared to that of an aberration-free cornea. The measures are integrated with preoperative corneal topography in order to calculate the required corrections.
Two companies, WaveLight Laser Technologies and Scwhind Technologies, have developed interfaces to the Dresden device and have begun international clinical studies. The March issue of the Journal of Refractive Surgery contains the first clinical data on three eyes using a WaveLight laser and the Dresden Wavefront Analyzer.
Also, the university has entered into an agreement with TechnoMed, who will market the Wavefront Analyzer as a stand-alone diagnostic device.

�        Nidek. Nidek is developing a diagnostic instrument that uses a combination of wavefront analysis and autorefraction to create a power map of the eye. Plans are under way to integrate the device with the company's scanning slit laser.

�        LaserSight. This development effort focuses on an integrated refractive workstation that includes front-to-back analysis of aberrations. The company recently acquired the intellectual property to make this possible from Premier Laser Systems and also hired several of the key development staff. They plan to integrate with the LaserScan LSX laser.

�        Tracey Technologies. This company's diagnostic device uses a scanning refractometer and ray tracing technology to test an array of 64 points. The unit has the added capability of a varying accommodative range from zero to infinity.

One step at a time

Wavefront technology and the potential of custom ablation patterns will be the focus of developers and surgeons for at least the next few years.

Laser center companies will fuel the demand for these products in an effort to make improved technology claims to prospective patients. However, progress in this area will be made one step at a time. FDA approval of a wavefront diagnostic tool integrated with a refractive laser isn't expected until late 2001 or early 2002.

David Harmon is president of Market Scope and the senior editor of Refractive Market Perspectives, a monthly newsletter on the refractive surgery industry. You can reach him at (314) 835-0600 or daveharmon@mktsc.