Lasers Take the Pain Out of Surgery By Howard Rausch

When you encounter a doctor in a hospi­tal these days, you can no longer be certain that he's a medical practitioner. He or she could very well be a Ph.D. in biology or, increasingly likely, in laser physics.

New photobiological capabilities are blurring the divisions between disciplines. They have already blurred the once clear distinction between surgery and medicine. And as they expand their contributions to diagnosis and to nonsurgical treatment, they give rise to a growing demand for specialists in lasers and in fiber optics that deliver light and retrieve information from inside the body.

Until the introduction of photobiological capabilities, the divisions between surgery and medicine were clear. For example, internists and pediatricians prescribed drugs, a medical treatment. Surgeons per­formed operations, causing anatomical changes in the body. The latter procedure often involved pain, danger, prolonged hos­pitalization, and high cost.

It's different today. Cardiologists per­form catheterizations. Gastroenterologists and lung specialists do endoscopy. Oph­thalmologists and urologists conduct doz­ens of types of operations in their offices that once required hospitalization. Inter­nists remove obstructive lesions in the windpipe and experiment with ways to use lasers to dissolve placques within arteries, eliminating the need for many heart bypass operations. Radiologists perform photorad¬iation of malignant tumors that have been treated with a drug to make them selec­tively receptive to the deadly laser light.

Surgery's shifting boundaries The line between surgery and medical

treatment is blurring. Nowhere is the dis­tinction less clear than in ophthalmology. Following a painless and quick perforation of an iris with an argon-ion laser to relieve the pressure of fluid behind the eye of a glaucoma victim, Roger Steinert at the Massachusetts Eye and Ear Infirmary in Boston remarked recently that the "proce­dure used to require an operation." The procedure remains an operation, or — sur­gery, according to technical and insurance definitions, but the eye is not opened with a knife, and the patient's discomfort is brief and minimal. There's no risk of infection, Steinert notes, because the only thing that enters the eye is light. And the operation's cost is measured in hundreds of dollars rather than thousands.

The eye, with its optical accessibility, is especially receptive to laser treatment. The earliest medical applications of lasers in­volved the retina, a network of nerve cells

in the back of the eye that transmits visual messages to the brain. In diabetics, the retina sometimes is miscued and over pro­duces new blood vessels. These new cap­illaries are always weak; eventually they break down, bleed, and cause complica­tions. The condition is a major cause of blindness.

"It doesn't work well to just close them with a laser, because new vessels grow in their place," Steinert explains. "So we put in 1,000 to 1,500 spots of laser burns and destroy enough retina so the chemical sig­nal that's causing blood-vessel formation is reduced."

Another major retinal application is for macular degeneration, a leading cause of new blindness — in contrast with heredi­tary blindness — in the United States. The macula, the tiny center of the retina, is used in reading and in distinguishing col­ors. In many people, the macula degen­erates with age. An advanced stage of degeneration involves the growth of fragile blood vessels under the retina where they break and bleed. Leakage of blood and other substances onto the macula can pro­duce serious irreversible damage to vision in a few weeks.

Closing these capillaries hasn't been easy. The argon laser's blue-green output is toxic; the blue part is particularly harmful to the retina, where it is absorbed by yellow pigment in the macular portion. "You don't want absorption in the retina," Stein­ert says. "You want to go through the retina to the layers underneath."

Another problem is the absorption of radiation by the blood that is usually pres­ent in such cases. To overcome these wave¬length barriers — to penetrate both blood and retina and allow absorption in the designated area below — krypton lasers that emit in the red are now commercially available.

The glamorous new laser for ophthal­mology, however, is the neodymium-yag, available to United States physicians only in the past year. When modelocked or Q¬switched, the yag laser can create optical breakdown, plasma formation, and a pres­sure wave that can separate tissue regard­less of pigmentation or opacity. An impor­tant application is removal of the posterior capsule of the lens following cataract sur­gery. The capsule is often left in at the time of surgery to reduce chances of complica­tions. But the capsule can cloud up later obstructing vision.

Steinert is also using the yag laser to manipulate lenses that have been im­planted in the eye after cataract surgery and have become caught in the wrong place. He uses yag pulses to "nudge" the lens into position.

He recalls an elderly patient with an eye severely damaged by glaucoma soon after cataract surgery and a cornea transplant. "She was a horrible risk for another opera­tion. But I knew we had the yag laser coming and decided to wait for it. We did treat her. Now this woman, who could hardly count fingers in front of her face, can sew, knit, and read with a magnifying glass.

Vision restored in eye of a patient who inflammation from glaucoma treatment, could hardly see a hand before her face. The membrane was cut open with a laser at Vertical beam of light comes from the Massachusetts Eye and Ear Infirmary, and examining equipment. Pupil had been to- the patient can now see through clear tally covered by gray membrane, a result of (black) center. Black area is open to light.

14 January/February OPTICS NEWS

Stereotactic device allows surgeon to locate a tumor three-dimensionally. Shown here with Developer Skip Jacques, a neurosur­geon at Huntington Medical Research In­stitute in Pasadena, the instrument com­bines CAT scanning with computer pro­cessing and, later, laser treatment. Scanning produces a series of surgical co­

ordinates via a metal ring with markers of different heights on outer rim. The markers, about 1 mm apart, show up in color-en­hanced picture on television screen, showing the precise size and location of a tumor in the brain, for example. In treatment, laser radiation is administered through a small hole in skull at tumor location.

Nonsurgical procedures In addition to simplifying surgical proce­

dures, laser technology is strengthening di­agnoses and helping to eliminate some sur­gery altogether.

Ophthalmologists use helium-neon la­sers to test, interferometrically, the poten­tial for vision. The beam penetrates opac­ity, in swollen corneas for example, and allows the physician to verify that the ret­ina is functioning. The patient sees interfer­ence fringes at the intersection of two parts of the split beam, which follow slightly different paths. With a cataract patient, the technique helps the physician ascertain how much of the visual problem is caused by the cataract and how much by a retinal defect. If the problem is in the retina, there may be no reason to remove the cataract.

For photoradiation therapy, the lasers most commonly used are scientific re­search models adapted for clinical use by the investigators themselves. Recently, however, both Coherent, Inc., and Cooper Medical Company have introduced clinical systems based on argon-pumped dye lasers which deliver their output through single-fiber optics with a variety of tips.

Laser makers supply only fibers with flat-cut ends, but users have developed a variety of tips. These deliver light either as a point source providing uniform spherical illumination, a uniform spot of uniform irradiance with sharp edges, or a cylindri­cal diffusing illumination along the fiber-tip length, typically 1 to 3 centimeters.

This system is used to detect preinvasive lung cancer by fluorescence bronchoscopy. By taking advantage of the selective reten­tion of hematoporphyrin derivative (Hpd) in malignant tissue, and of the drug's emis­sion of red fluorescence upon excitation by violet light, the system can visualize an Hpd concentration as small as 0.1 micro­gram per milliliter in a well only 0.1 mill i­meter deep and 1.5 millimeter wide. The system uses a krypton-ion laser to excite the drug and an image intensifier to visual­ize the emitted low-level red fluorescence through the bronchoscope. According to Developer Daniel R. Doiron, a bioengineer at the Los Angeles County, University of Southern California Medical Center, the system allows detection of the cancer be­fore it is large enough to be detected by X -ray. If the tumor is large enough to be detected by X-ray, Doiron explains, the survival rate following surgery is poor.

In studies of gastric ulcers, Takenobu Kamada and colleagues at the Osaka Uni­versity Medical School in Japan have used reflectance spectrophotometry during en­doscopy to monitor blood flow. They found consistent changes: lower volume during the ulcer's active stage and larger volume during healing. Measurements were made with an optical-fiber bundle on the lesion's surface.

Kamada's group has developed a nonin­vasive version based on thermographic de­tection of infrared radiation from tissue heated with an argon-ion laser.

A more controversial use for lasers is wound healing, a technique pioneered by Endre Mester in Hungary and now being adopted in China. Exposure to helium-neon laser radiation hastens recovery from skin tumors, cancers, and other surface wounds, Mester contends. Research groups else­where, however, have failed to duplicate his results. A study at the Letterman Army Institute of Research in San Francisco con­cluded that He-Ne irradiation of wounds "increases certain aspects of healing in the early stages, but not to such a degree as to be clinically applicable." Authors John S. Surinchak, et al., writing in Lasers in Sur­gery and Medicine, note successes in accel­erating healing of chronic ulcers. They conclude that the "laser may have a prom­ising future in the clinical environment, but its role is currently limited by the lack of detailed information on dosimetry."

The future Dramatic accomplishments are expect­

ed to burgeon as medical and physical researchers collaborate to exploit the la­ser's potential for selective photochemistry rather than only its thermal properties. "We want to use the light to do something more specific than to cook the tissue," explains James Richter at Massachusetts General Hospital. "Lasers can interact with tissues in a variety of ways, activating specific biochemical sequences, similar to photosynthesis in plants. Light does that quite specifically without endangering the tissue." Light can induce enzymes much as it induces formation of melanin in the skin in the process known as tanning. Psoriasis can be treated with incoherent light sources at specific wavelengths; and Rich­

ter contends that lasers can do the same thing more selectively.

John A . Parrish, a dermatologist who directs the new laser laboratory at Massa­chusetts General, considers the concept of photochemotherapy to be "more important than any present application." The optical portion of the spectrum, from the ultravio­let through the near infrared, can produce a large variety of highly specific biologic effects, he says. The quantum energy of photons at these wavelengths corresponds to the activation of specific molecules or chromophores, usually causing specific al­terations of those absorbing centers. Hence it should be possible to "dr ive" a specific photochemical reaction to the exclusion of others by supplying light to specific chro­mophores at the right wavelengths. "We are only beginning to utilize this potential," Parrish reports.

Crit ical to many laser applications is the delivery medium, often an optical fiber or a bundle of fibers. "Med i ca l " fibers have low loss, comparable with those used in tele­communications. If loss is too high, ener­gies required for many medical applica­tions could cause fibers to self-destruct. As demand increased, so did the supply of suitable fiber. "In 1973 we had to beg Corning Glass Works for the fiber because there was no medical market for it," recalls David Auth, a pioneer in medical-laser research at the University of Washington. Today optical fibers perform four groups of functions in the body: they illuminate the scene, retrieve images, deliver concen­trated energy, and sense physical aspects of the patient's condition such as tempera­ture, pressure, flow velocity, and spectral absorption.

OPTICS NEWS January/February 15