REFRACTIVE SURGERY UPDATE

Beyond Topography-Guided Ablation

by Paul M. Karpecki, O.D.

Can we improve on 20/20 vision? Imagine referring professional athletes and other patients for refractive surgery and expecting 20/12 or 20/10 vision. New technologies that improve on corneal measurements and even expand measurement capabilities to encompass the entire visual system may one day justify these expectations.

The Bausch & Lomb Technolas 217 laser uses a 2mm spot size to ablate a smooth surface on the cornea. The system is the first designed specifically to accommodate the LASIK procedure. B&L recently purchased Orbtek (Salt Lake City, Utah), which manufactures the Orbscan II corneal topography unit.

Orbtek topography provides more information than previous generation topographers. This includes elevation of the front (see top left map) and back surfaces (top right), corneal thickness (bottom right) and topography (bottom left).  By combining the Orbscan with ultrasound to determine axial length and lens thickness, you can determine a simulation of the retinal point spread (RPS), or the distance between the specific cones.

Orbtek is also working on a simulated measurement technique called "wave-front ablation vision enhancement" or WAVE. Rather than relying solely on corneal measurements, WAVE will treat the vision system by targeting ideal postoperative topography with optical RPS. Reverse ray tracing creates patterns involving all aspects of the visual system from corneal Orbscan measurements to lens index and thickness to retinal spacing. B&L is currently awaiting FDA approval on the Technolas 217, while the experimental WAVE system has yet to begin human clinical trials.

Another company showing promise beyond topography-guided ablation is Autonomous Technology Inc., a subsidiary of Summit Technology Inc. Last year, Autonomous became the third excimer laser company to receive FDA approval. The LADARVision excimer laser was approved for treatment of myopia up to -10.00D and astigmatism up to 4.00D. The laser uses a 0.8mm to 0.1mm small spot beam and a NASA-developed eye tracker.

The system uses software-controlled ablation algorithms to create "shot patterns," which direct each of the thousands of individual pulses to a pre-determined location. This allows a smoother overlapping pattern and places the spots where desired for optimal vision results. The LADARVision eye tracker checks the position of the eye 4,000 times a second, and then adjusts the position of the laser pulse. This system can compensate for the smallest of eye movements, including saccades.

The most exciting development at Autonomous may be the custom cornea project. It uses a proprietary wave-front sensor to actually measure the total aberrations of the eye. A laser pulse travels through the cornea, lens, media and retina, and the system then measures the returning retinal waves. The Custom Cornea measurement device (CCMD) currently used on patients shows that those with above-average vision have significantly fewer aberrations when considering the entire visual system from cornea to retina.

Information like this, along with improvements in laser application, may have your patients expecting 20/10 vision.

Daniel S. Durrie, M.D., contributed to this article.

The authors have no financial interest in any of the products mentioned above. Hunkeler Eye Centers is currently studying the B&L Technolas 217 and the Autonomous LADARVision excimer at its Hunkeler Vision Research Center.