New Wavefront Devices Could Mean Superior Vision for LASIK Patients
Like a fingerprint, the human eye has characteristics unique to each individual. But these distinctions do more than differentiate us from others. They also can keep us from achieving optimum vision -- even after refractive surgeries.
A new, noninvasive technology called wavefront analysis seeks to change that. Wavefront analysis creates a map of the eye, exhibiting any abnormalities, known as aberrations, which prevent maximum vision.
The U.S. Food and Drug Administration has cleared the technology for diagnostic purposes. But it is the marriage of wavefront analysis with excimer lasers that excites surgeons. The union would produce a customized procedure that can improve vision beyond today's limits, say proponents.
"You can take a patient with decreased vision and formulate a special treatment plan to give them better vision than they could not get with contact lenses or spectacles," says John Doane, M.D., of Discover Vision Centers in Kansas City, Mo., an FDA clinical investigator for VISX, creator of the WaveScan Wavefront System.
Doane compared undergoing current LASIK, or laser-assisted in situ keratomileusis, surgery to buying new shoes. Size 10 shoes are identical, no matter where you purchase them. But people don't share identical foot shapes. Indeed the shape can vary from your left foot to your right foot.
The same is true of the eye. Even though you may have the same prescription as someone else, your eyes are not the same. Everyone has aberrations.
"These aberrations can be anywhere in the visual system -- on the back of the cornea, on the retina," explains David Hardten, M.D. of Minnesota Eye Consultants in Minneapolis, Minn., another investigator for VISX. "When patients have a lot of aberrations, they may not see very well - even with contacts or glasses - because of the distortion."
Wavefront devices detect these aberrations. Most of the devices work on the same principle, says Daniel Neal, vice president and technical director of WaveFront Sciences, the Albuquerque, N.M., manufacturer of the Complete Ophthalmic Analysis System.
Optics project light into the patient's eye. Then a Hartmann-Shack sensor precisely analyzes the returning wavefront. Originally used by astronomers to collect data about distant stars, the sensor contains thousands of tiny lenslets that create patterns.
The resulting "fingerprint" marks how the light was bent. The data not only exhibits the refractive errors, it also measures the sphere, cylinder, and axis.
The non-touch procedure just takes minutes, Doane says. And it's painless. The patient simply sits before the device, which is about the same size as a traditional auto refractor.
Although the technology is proving valuable as a diagnostic tool, the big payoff will come from incorporating it with LASIK procedures, says Thomas McKay, the marketing manager for VISX's WaveScan system.
VISX has conducted two sets of trials in Germany and the United Kingdom. "The results were very promising," he says. "In the first batch of U.K. patients, the laser/wavefront treatments were able to fix de-centered ablations, and the patients saw 20/15."
The laser draws on the wavefront data to create a custom surgical pattern. "The more precise you are able to do this, the more likely that you are going to be able to improve vision beyond the so-called normal limits of today," McKay says.
VISX isn't the only company pursuing the union of wavefront and LASIK. WaveFront Sciences is partnering with Asclepton-Meditec, a German company that sells laser systems, to create a wavefront-guided laser. Alcon Summit Autonomous is investigating the marriage of its CustomCornea Wavefront System to its LADAR Vision System.
Patients excited about the wavefront-guided LASIK surgery may need to temper their enthusiasm. The FDA may not grant approval for wavefront-enhanced lasers until 2002, McKay says.
So should you wait to undergo LASIK surgery? Not necessarily. "LASIK is the driver on the golf course," Hardten says. "Wavefront is the putter."
Current laser technologies can correct vision up to 98 or 99 percent, he explains. Aberrations only account for about two to three percent of vision loss.
While that might seem minimal, the percentage can make a critical difference to patients who did not achieve superior results from LASIK. Doctors can use postoperative wavefront analysis to determine the reason.
Wavefront technology also has pre-operative value, Neal adds. Consider LASIK screening. With the wavefront data, doctors can use the laser to fabricate plastic lenses. The special glasses would let patients take their eyes through a LASIK-simulated test drive.
"You can test the process all the way through to makes sure you are right," he says. "Patients can tell you how they like it."
Doane agrees. The patient has an active say in the prescription selection.
Not all aberrations are correctable, Doane points out. A deep corneal scar, for instance, requires a corneal transplant, not LASIK surgery.
"This won't help everyone," he concludes. "But it should help well over 95, if not 99, percent. It raises the bar."