Santa Clara, CA—The reporter slumped wearily into his seat on a red-eye flight from California to Boston. After two days of interviewing engineers and other experts on the technology behind laser vision correction, it was time to let the mind relax and think of something else—maybe even get some sleep. But not quite yet. Across the aisle two young women were chatting excitedly about their plans for the new year. "I'll tell you what I'm going to do with my Christmas bonus," said one of them. "I'm going to get that laser treatment for my eyes. I've had it with these contacts."
No matter where you go these days, you will run into people singing the praises of technology's latest medical miracle: laser vision correction (LVC). In a matter of minutes, this remarkable out-patient surgery gives most people the pleasure and freedom of 20/20 vision without the daily annoyances of contact lens and glasses.
"It's absolutely wonderful," says Michael Huffmaster, a 37-year-old Missouri engineer who had the surgery last fall. "I am amazed at how a 30-minute procedure can so dramatically change your life."
Approved by the FDA barely five years ago in the U.S., laser vision correction is fast becoming one of the most common operations in the country. Ophthalmologists performed some 1.4 million LVC procedures in 2000—a 60% increase from 1999. Industry experts predict the number will grow to at least 1.8 million in 2001. And this does not include the secondary use of the technology for treating corneal diseases and other pathologies of the eye.
The potential market is both enormous and lucrative. LaserVision Centers, a major provider of lasers and equipment to eye surgeons, notes that nearly 160 million people in the U.S. need corrective lenses to cope with nearsightedness, farsightedness or astigmatism. The dollars spent on glasses, contacts, and other eye care products total more than $16 billion annually.
"If the medical community were treating even 2% of the possible market, our centers would be operating around the clock," says Dr. David Eldridge, executive vice president of Clinical Services for TLC Vision Centers, whose revenues jumped 37% in fiscal 2000.
Sculpting the cornea. While there are different surgical techniques used, most commonly LASIK and PRK (see sidebar), the LVC procedure uses cool, ultraviolet rays from an excimer laser to delicately remove tissue from the cornea, the clear, outermost layer of the eye. Good natural vision occurs when the cornea refracts light to a single point on the retina at the back of the eye. About 60% of us, however, have misshapen corneas. This causes the light to be refracted improperly, leading to blurred or distorted vision. The laser sculpts the cornea to correct this problem. In effect, LVC actually transfers your current eyeglass or contact lens prescription onto the surface of your eye.
As is the case with virtually every medical innovation, most of the credit for the amazing changes that LVC brings to patients goes to the practitioners—the skilled ophthalmologists who do the surgery. But talk to many of those eye surgeons—including those from the most prestigious treatment centers in the U.S.—and the name of one design engineer keeps coming up: Charles R. Munnerlyn. The quiet, unassuming Texan not only designed and built the first working excimer laser system for vision correction in 1985, but he also developed the core mathematical formulas that dictate the amount of corneal tissue to be removed by the laser. What's more, together with a small group of engineering and medical colleagues, he founded VISX, now the world's largest manufacturer of laser-based vision correction systems.
"Charles Munnerlyn was one of the founding fathers of laser vision correction," notes Dr. Manus Kraff, professor of clinical ophthalmology at Northwestern University. "It was his basic engineering that built the first excimer laser system, and his hand continues to shape many of the innovations in this field."
Adds Jack Klobnak, CEO of LaserVisionCenters, a major VISX customer: "Every time I see Charles I thank him. This industry wouldn't have developed without his brilliant engineering work."
Sophisticated system. LVC systems represent one of the medical industry's most complex technologies. For example, the Star S3, the most recent VISX model, consists of about 4000 total parts and some 250 subassemblies, according to Doug Post, VP of Operations. Designed to fit comfortably in about a 10 x 10 foot area, the PC-based system includes:
Keyboard and monitor for calibrating and operating the machine, as well as entering and analyzing data on the patient's eyes before and after the procedure.
Excimer laser system, including a chamber with supply of argon and fluorine gas, vacuum pump, and fan to circulate the gas across electrodes to produce the laser light.
Optical delivery system, incorporating a proprietary network of lenses and other components to focus the laser beam on the eye.
Physician's station, including a binocular-style surgical microscope positioned directly above the patient's eye.
Adjustable patient's chair, which reclines to a prone position and includes a special pneumatic pillow to hold the head in a stable position.
All this is supported "under the hood" by a vast array of VISX-designed circuit boards, as well as a long list of actuators, miniature motors, controllers, sensors, leak detectors, power supplies, safety switches, fiber-optic cabling, EMI/RFI shielding materials, molded plastics, and sheet metal housings. Software code for the system embraces everything from motion control to operator interfaces to the actual algorithms that drive the precise tissue-removal pattern for a specific patient. And, notes Post, since less populated areas can't support a full-time laser treatment center, many VISX units are trucked from place to place. "This is delicate equipment," he adds, "but it is rugged enough to be shipped about with only minimal calibration."
Needless to say, this medical marvel did not develop overnight. In what Charles Munnerlyn describes as "the long road to laser refractive surgery," it took 10 years of hard work, $100 million in investment, and a mountain of FDA documentation before VISX sold its first commercial system for therapeutic purposes in late 1995. Along the way, Munnerlyn often spent as much time searching for money to keep the project alive as he did developing the technology.
Texas towns. Munnerlyn didn't start out dreaming about medical inventions. His first—and abiding love—is the field of optics. The son of a maintenance engineer whose work on natural gas pumping stations took the family to a series of rural Texas towns, Munnerlyn recalls discovering an old pair of glasses in a drawer when he was about 12 years old. He put one lens in each end of a tube and spied a cow near his home. "I was surprised at the result. The cow was upside down," he recalls with a chuckle.
Trying to find out why the cow was upside down launched an enduring fascination with optics that started with a homemade telescope at age 13 and blossomed through a physics degree at Texas A & M and a Ph.D. in optical engineering from the prestigious Institute of Optics at the University of Rochester.
"The institute was a tremendous spur to my career," he recalls. "It helped me develop an intuitive feel for what would work. If there were optical engineering challenges in the world, I felt the institute prepared me to solve them." Indeed, his Ph.D. thesis, involving precise calculations for grinding and polishing large mirrors used in advanced telescopes, foreshadowed the calculations he would one day make on ablating minute particles of tissue from the human eye. After receiving his engineering doctorate in 1969, Munnerlyn stayed in the Rochester area as head of R & D for Tropel, a company that designed prototype custom lenses for applications that included Xerox copiers, Polaroid cameras, space satellites, and semiconductor photolithography. But the company wanted something more from Munnerlyn: Develop a product with high-volume commercial potential.
Munnerlyn responded in the early 1970s with the first automatic digital device to measure refractive errors in the eye. Called the Dioptron, the instrument directs a light source into the eye of a patient as he peers through an eyepiece. Light from the pattern reflected by the retina produces an analog signal, which is converted to a digital signal and fed into a computer. The computer in turn fits a sine wave to the selected signal, then calculates the refractive error from the sine wave.
This new device, which Munnerlyn and his colleagues developed with input from ophthalmologist Hobart Lerner, substantially reduced the time it took doctors and optometrists to determine the amount of correction needed for a given patient. Moreover, it is a more objective measurement of refractive error than the phoroptor—an instrument containing multiple lenses that patients try in alternating fashion until the right prescription is found. Now, the common practice in an eye exam is to use the automatic refractor first, followed by a short session with the phoroptor.
The Dioptron was one of the first devices to incorporate an Intel microprocessor, and Munnerlyn recalls hosting a dinner at his Fairport, NY, home for the chipmaker's famous founder, Robert Noyce. "At the time we didn't even have a dining room set,'' remembers Munnerlyn. "I think we seated him at a card table."
Coherent bought Tropel in 1972 and moved the medical operation to Palo Alto, CA in 1975. Munnerlyn moved with it, becoming R & D director for the company's medical division. There he continued to develop new optical-based products like the Permitron, used to diagnose glaucoma. He also got his first experiences with medical lasers for ophthalmology, such as an argon-based system for cauterizing ruptured blood vessels in the eye, a common problem among diabetics.
Budding entrepreneur. Beginning in 1978, however, Munnerlyn began a decade-long period in which he struggled with a desire to start his own businesses, while at the same time perfecting his ideas for laser-based systems for vision correction. Together with Terry Clapham, an electrical engineer who was his trusted collaborator for 25 years dating back to the early days of Tropel, Munnerlyn quit Coherent and started a business making a hand-held digital instrument called the Digiton tonometer. Family physicians used it to detect pressure in the eye and the onset of glaucoma. "I was the salesman, going to medical shows with a little booth, and Terry would manufacture the $500 units in his bedroom.''
Out of funds, the two engineers returned after a year and a half to Coherent, where they turned their attention in earnest to the development of medical lasers. Munnerlyn holds a key patent for a pulsed YAG laser. Among its targeted applications, the laser directs carefully positioned bursts of light energy to destroy the sight-impairing membrane that forms in many patients following cataract surgery.
Frustrated by the pace of development at Coherent, Munnerlyn and Clapham struck out on their own once more in 1983 to improve the YAG laser design. But once again, they hit financial roadblocks. "What makes you think you can do better than what 15 others are trying to do?" challenged the venture capitalists.
The two finally got a half million dollars in backing from a company called CooperVision, which wanted the rights to sell the system when it was successfully developed. However, while Munnerlyn and Clapham raced to develop working prototypes for the crucial annual fall meeting of the American Academy of Ophthalmology in 1983, CooperVision was secretly working on a competing system at another California location.
"Our system sold for $65,000, compared to $45,000 for the units the company was developing," notes Munnerlyn. "But the ophthalmologists at the meeting preferred our design."
Key partner. About the same time, the two engineers met Stephen Trokel, an ophthalmologist based at Columbia-Presbyterian Medical Center in New York. With an undergraduate degree in engineering physics, Trokel had already edited a book on the use of YAG lasers in microsurgery and talked to Munnerlyn about the use of excimer lasers in such applications as removing corneal scars. He also envisioned using lasers for vision correction as an alternative to the then new and controversial field of Radial Keratotomy, in which the surgeon corrects vision by making incisions on the periphery of the cornea.
Even more important, Trokel was becoming increasingly enthusiastic about another type of laser—the excimer. Operating in the ultraviolet range, the excimer can break apart and vaporize the collagen molecules of the cornea without generating the heat associated with other lasers. Moreover, there is no danger of its beams penetrating the eye and causing damage to the retina. With a 193 nanometer wave length and operating in pulses lasting several billionths of a second, the laser removes only one quarter of a micron per pulse. In an LVC procedure to correct a moderate case of nearsightedness—say a refractive error of -5 diopters—the surgeon removes corneal tissue to a depth of about 60 microns, about half the width of a human hair. The entire cornea has a thickness of about 500 microns. Moreover, the diameter of the treatment area is typically just 6 millimeters.
"This excimer has an almost magical quality to it," points out Dr. Trokel. "When I first discussed it with Charles in 1983, he saw better than I did how it could revolutionize eye surgery. And he could envision the engineering that would make it all possible."
Munnerlyn and Clapham set about working with Trokel and other prominent ophthalmologists to develop a working excimer laser for corneal surgery, encouraged along the way by results of animal studies conducted at such centers as Columbia-Presbyterian and Louisiana State University. Studies on rabbits, for example, showed excellent results, with corneas remaining clear with ablation depths up to 50 microns. By 1986, they had completed two working prototypes for an ophthalmology research center in Canada. Munnerlyn also had written a seminal research paper in which he coined the phrase "Photorefractive Keratectomy"—correcting refractive errors by using laser light to surgically remove corneal tissue. The paper, among other points, included his ideas for the optimum beam delivery system, as well as the formulas for ablating the correct amount of corneal tissue. It was rejected by the American Journal of Ophthalmology as being "too technical."
Rotating beam. Among Munnerlyn's major contributions to the LVC field are his many innovations in the optical designs for delivering the laser beams to the cornea. Instead of scanning a small laser beam spot in a pattern that moves around the surface of the cornea, as some researchers recommended, Munnerlyn sized the laser beam to coincide with the entire area to be shaped. This eliminated the problems of gaps and rough overlaps between beam spots and achieved a smoother, more uniform ablation. As Munnerlyn explains it: "My thought was this: If you can remove tissue precisely with the excimer laser, why not do it in the shape of a lens?"
To achieve that goal, he employed such techniques as a variable diameter aperture, which can concentrically expand or decrease the size of the beam, depending on the correction needed. To correct for myopia, for example, more tissue needs to be removed from the center of the cornea and less at the periphery. He also devised a system for rotating the beam during the ablation to average out beam density variations.
"The excimer system we developed was the culmination of everything that Charles and I had learned over 20 years of developing optical devices,'' notes Clapham. "And the laser itself represents just 20% of the system. You've also got such things as cryogenic cooling, sophisticated software, electro-optical modules, the whole optical delivery system, toxic gases—and the need to put all of it in a safe, user-friendly package for a doctor's office."
How much confidence does Clapham have in the technology? He underwent LVC himself several years ago in Canada—gratefully shedding his "coke bottle glasses" once and for all.
Despite the many frustrations that occurred along the way, Clapham stresses that Munnerlyn would inevitably come up with practical solutions, not just in his specialty—optical systems—but in hardware and software as well. Then, too, he bore the brunt of efforts to raise money to keep the work going. When CooperVision decided to get out of the laser business in 1987, the two engineers put up virtually all their assets as collateral to buy the excimer laser technology from the company and start their own company, VISX.
By that time, the LSU researchers, led by Dr. Herbert Kaufman and Dr. Marguerite McDonald, had used excimer systems designed by Munnerlyn to conduct the first tissue removal experiments on human eyes—first with a woman whose eye was scheduled for removal because of a tumor, and then with several others with good corneas but who were blind because of damage to the back of the eye. Finally, under an FDA investigational device exemption, Dr. McDonald performed the first PRK on a sighted eye in 1987.
"Charles is the giant in this field,'' says Dr. Kaufman. "Others wrote papers about the technology, but Charles actually showed it could work by developing the fundamental machine." Dr. McDonald calls Munnerlyn "the premier biomedical engineer in this country."
Even though FDA approval was still years away, Munnerlyn and Clapham took VISX public in 1989, raising $4 million. More resources came in 1990, when the company merged with a competing firm, Taunton Technologies. "Rather than spend all our money fighting each other over patent infringement, we decided it made sense to get together," recalls Munnerlyn, who became the first president of the combined company.
Meanwhile, VISX research efforts with the excimer laser were expanding to include procedures to remove corneal scars. "The laser procedure is often a better alternative to expensive and time consuming corneal transplants," notes ophthalmologist Walter Stark of the Wilmer Eye Institute at Johns Hopkins University. In fact, the first FDA approval for the VISX excimer laser, granted in 1995, was for such therapeutic uses.
Leading the pack. It was not until March 1996 that FDA finally gave VISX commercial approval to use its excimer system to correct myopia (nearsightedness), the most common vision problem. In the years since, the company also has gained important FDA approvals to correct hyperopia (farsightedness) and astigmatism. While there are several major competitors in the business, most notably ALCON, Nidek, LaserSight, and Bausch & Lomb, VISX has risen to the number one spot in the industry. "Our success goes right back to Charles," says VISX Chairman Mark Logan. "This technology wouldn't have been invented without the collective genius of Munnerlyn, Trokel, and Clapham."
About two thirds of LVC procedures in the U.S. are performed with VISX equipment, and the company has shipped more than 1000 lasers worldwide. Revenues come both from the sales of the laser systems, which list for about $500,000, plus a $100 royalty fee that VISX collects each time an LVC procedure is performed. Sales in the most recent fiscal year totaled $271 million.
"I believe that VISX technology is far superior to anything on the market," says Dr. Kraff of Northwestern, "and the company continues to come up with important innovations."
Among the improvements VISX has made to its systems over the years:
Introduction of an optical module that splits the laser light into seven small beams that rotate across the cornea to produce a smooth, virtually featureless ablation. Studies show that smoothness impacts quality of vision, the rate of rehabilitation after surgery, and refractive stability.
New software algorithms that allow for more effective treatment of people with corneal irregularities.
Faster pulse frequencies that shorten the time needed for procedures. Total laser time is generally less than 30 seconds per eye.
Introduction of new "eye tracker" technology, a 3D infrared tracker that monitors a patient's eye movement during treatment. Whenever eye movement is within 1.5 millimeters of the ideal optical alignment, the laser system compensates by repositioning the beam. If the eye moves outside of this range, the ablation process automatically pauses until the patient focuses properly on the fixation light.
While Munnerlyn, at age 60, now works only part-time at VISX, his guiding hand can still be seen in many
of these innovations. Company scientists and engineers note that Charles continues to maintain a thorough understanding of the entire system and advises them at important milestones on key projects.
"He's a tremendous resource who is always available to answer questions and help sort out problems," notes software engineer Richard Hofer.
Kingman Yee, VISX principal scientist, adds that it was Munnerlyn who suggested that the new eye tracker technology employ two cameras, instead of only one as originally planned.
Future advances. Though proud of their technology, Munnerlyn and his colleagues are looking ahead to even more LVC advances. Currently, according to FDA data, 98% of those receiving treatment for mild or moderate myopia achieve 20/40 vision or better, enough to pass a driver's exam without corrective lenses in most states. About 75% gain 20/20 vision or better.
Even so, because of corneal irregularities and individual differences in the makeup of the entire eye, researchers are looking for diagnostic and treatment tools that will allow them to achieve a more customized ablation and even better results. For example, many in the industry are excited about a new technology called wavefront, developed by German physicist Josef Bille of the University of Heidelberg. This technology analyzes sheets of light as they pass through the eye. Instead of the relatively flat sheets that pass through the eye of a person with good vision, the pattern for someone with refractive defects will be represented by irregular, curved waves. With this new "fingerprint of the eye," produced by new diagnostic devices like the VISX WaveScan, surgeons will be able to achieve substantially better ablation results in many patients—including eyesight of 20/15 or even 20/10, so-called "perfect vision."
For Munnerlyn, it's the satisfaction of seeing the benefits of this technology virtually every day that keeps him involved. "When I am playing golf with strangers, they almost always comment that they or close friends have had their eyes treated to get rid of glasses or contacts," says Charles, who is currently working on improvements in the fixation light that patients focus on during LVC. "It is most gratifying to have been able to help make these advances in medical technology."
VISX engineers have modified the optics in the company's laser vision correction systems over the years, but this diagram from a 1996 Charles Munnerlyn patent shows the basic elements of a typical optical delivery system to correct hyperopia (farsightedness).
The system includes: an excimer laser, a mask located along the optical path to shape the beam to a desired profile, and a method for displacing the profiled beam from the path to an offset position. In addition, the angular position of the offset beam needs to be varied around a center of rotation that corresponds to the center of the area to be ablated by the laser beam.
As seen in the drawing, the beam is reflected by two mirrors and enters a spatial integrator, where it is modified in cross section to improve the beam uniformity. The beam is then reflected by two more mirrors before passing through a dove prism, which acts as a rotating device. A mask mounted on this device controls the size and shape of the beam, which is reflected by another mirror and enters an offset control unit containing an imaging lens. Finally, the offset profiled image exits from the control unit and is reflected by a mirror onto the patient's eye.
Munnerlyn notes in the patent that the invention offers the advantage of a relatively wide area of coverage without requiring a laser beam of a size approximately equal to the treatment area. Result: the design requires substantially less energy, which extends the life of the optical components.
In addition, the design still allows for a large enough beam to span from the center of the rotation to the outer boundaries of the treatment zone. For most human eyes, the largest treatment area is approximately 10 millimeters. With this design, a laser with a beam diameter of 6 millimeters will easily provide the desired tissue ablation.
A preview of
Thinking about laser vision correction?
Most people choose the LASIK procedure, short for Laser In-situ Keratectomy.
Like the older technique, Photorefractive Keratectomy (PRK), LASIK reshapes the cornea with the cool beams of an excimer laser to correct for irregularities that cause improper refraction of light as it passes through to the retina.
In PRK, the surgeon first removes the epithelium, the outermost layer of the cornea, and then directs the laser at the exposed surface of the next region of tissue, known as Bowman's layer. While this procedure has produced excellent results in tens of thousands of patients worldwide, there tends to be some discomfort in the healing process as the cells of the epithelium regenerate. Typically, a clear "bandage" contact lens is placed over the treated eye for protection during the first few days of healing.
In the LASIK procedure, the surgeon does not remove the epithelium layer. Instead, he uses an automated instrument, called a microkeratome, to make a thin flap in the outer cornea. With the flap folded back, the surgeon ablates the tissue, just as in PRK. After the correct amount of tissue is removed, the flap is closed. Most patients prefer the technique because the eye heals very rapidly, and clear vision is restored within a few days—versus a few weeks for PRK. What's more, with LASIK, patients require fewer post-operative visits and have less need for anti-inflammatory eye drops.
Both procedures take only a few minutes, are painless, and follow a thorough battery of tests, including an automated mapping of the eye's topography. At the time of treatment, a patient's eyelids and lashes are cleaned, and antibiotic, anti-inflammatory and anesthetic drops are placed in the eye.
Upon entering the laser suite, the patient reclines flat on a special chair—head situated directly under a surgical microscope. Data from the eye examinations are used to program the computer software in the laser unit. The computer automatically calculates the amount and pattern of corneal tissue to be removed. With the patient focusing on a fixation light, the ophthalmologist activates the laser pulses, which come in rapid succession, each lasting several billionths of a second. Typically, each eye is exposed to the layer beams for just 30 seconds.
For most people who have gone through life either squinting or hassling with ill-fitting glasses or irritating contacts, laser vision correction is nothing short of a godsend.
"I like to hunt, fish, and play basketball," says Lee Tharp, a 40-year-old environmental engineer from Jefferson City, MO, "and contacts and glasses were becoming more and more of nuisance."
So after a year of thinking about it, he went ahead with the surgery last fall. "I flew into St. Louis, had the surgery, stayed overnight, and had a check-up in the morning," recalls Tharp. "That's all there was to it."
And the results? "I'm ecstatic," says Tharp, who figures that he spent $300 to $400 annually on contacts, solution, and other eye-care products. "Not only do I see much better, but I am not risking infection by sticking my fingers in my eyes every morning to put contacts in."
Tharp paid $2,000 to have both eyes corrected, which is at the low end of fees charged by centers with FDA-approved equipment and experienced ophthalmologists. Many facilities still charge as much as $2,000 to $2,500 per eye, particularly where the volume of patients is relatively low. At this time, most insurance plans do not cover laser vision correction.
Bargain hunters. Dr. David Eldridge, executive VP of Clinical Services for TLC Vision Centers, one of the country's largest providers of equipment for laser vision correction, cautions consumers to "beware of the bottom feeders" who are charging as low as $500 per eye. Some providers may be short-changing consumers on pre- and post-op consultations, he warns, or cutting corners by employing such practices as using the same microkeratome blade for several surgeries. In the LASIK procedure, the ophthalmologist uses the microkeratome to make an ultra-thin flap in the outermost layer of the cornea, then reshapes the exposed surface with the laser beam.
One prominent proponent of laser vision correction is Tiger Woods, who tops a long list of sports stars and entertainers who have undergone the procedure. After LASIK surgery in October 1999 with VISX equipment, Tiger, who now tests better than 20-20 vision, put together a record-shattering 2000 on the PGA tour, earning more than $9 million. "When I recall how poor my eyesight was my entire life, I feel like I've experienced a miracle," said Woods in a testimonial. "The hole and everything now look bigger."
Ophthalmologists recommend that people seeking the treatment be at least 21 years old, have a stable prescription for about a year, have healthy eyes, and be in good general health. With today's equipment, many people with even extreme nearsightedness or farsightedness can realize marked improvement in their vision. Overall, studies show that about 98% of those with mild to moderate myopia, for example, can expect an improvement to at least 20/40 vision. About 75% will enjoy 20/20 or better.
But what if you need bifocals to correct your vision for both distance and reading? While some people choose to have one eye corrected for distance and the other for close work—an option known as "monovision"—LVC technology cannot currently correct both conditions in both eyes. Charles Munnerlyn, who developed the first excimer laser for vision correction, falls into this category. Since today's technology can't free him entirely from corrective lenses, he is still evaluating treatment options.
As for risks, experts cannot cite any instances of blindness resulting from laser surgery for vision correction. In less than 1% of the cases, however, patients may experience chronic problems such as blurred vision, night glare, or loss of best-corrected vision.
The best advice: Research the procedure and pick an experienced surgeon who uses FDA-approved equipment.