Medical Uses of Lasers
Medical Uses of Lasers
In the early days of lasers it came as a surprise that these tools of light could be used in the science of medicine, since no one envisioned that they might be able to heal or otherwise improve people's physical well-being. But doctors and medical researchers quickly began to see the possibilities, and the number of uses for medical lasers multiplied over the years. Among other applications, these include cutting into tissue in surgical procedures; reshaping the cornea of the eye to improve sight; cleaning clogged arteries; burning away cavities and whitening the teeth; removing unwanted hair, wrinkles, birthmarks, and freckles; and reshaping the face in plastic surgery procedures.
The Advent of the "Laser Scalpel"
Early experimenters with medical lasers pointed out that there are surgical operations that are difficult to perform with the conventional scalpel and that a laser beam might be used instead. Initial trials showed that a finely focused beam from a carbon dioxide gas laser could cut through human tissue easily and neatly. The surgeon could direct the beam from any angle by using a mirror mounted on a movable metal arm.
Several advantages of laser surgery quickly became apparent. First, the light beam is consistent, which means that it gives off the same amount of energy from one second to the next. So as long as the beam is moving along, the cut it makes (the incision) does not vary in depth; whereas when using a scalpel a doctor can accidentally make part of the incision too deep. A second advantage of the surgical laser is that the hot beam cauterizes, or seals off, the open blood vessels as it moves along. (This works well mainly for small vessels, such as those in the skin. The doctor still has to seal off the larger blood vessels using conventional methods.) Still another advantage is that the cells in human tissue do not conduct heat very well, so the skin or any other tissue near the laser incision does not get very hot and is not affected by the beam. This advantage of laser surgery is very helpful when a doctor must operate on a tiny area that is surrounded by healthy tissue or organs.
It should be pointed out that the "laser scalpel" is not necessarily the best tool to use in every operation. Some doctors feel that while the laser is useful in some situations, it will never totally replace the scalpel. Others are more optimistic and see a day when more advanced lasers will make the scalpel a thing of the past.
The second of these views may prove to be the most accurate, for surgical use of lasers is rapidly advancing. At first, lasers were considered most effective in operating on areas that are easy to reach—areas on the body's exterior, including the skin, mouth, nose, ears, and eyes. But in recent years doctors have demonstrated remarkable progress in developing laser techniques for use in internal exploration and surgery. Of course, in order to be able to direct the laser beam the doctor must be able to see inside the body. In some cases this is a simple matter of making an incision and opening up the area to be operated on. But there are situations in which this step can be avoided.
Cleaning Arteries with Light
For instance, lasers are increasingly used to clean plaque from people's arteries. Plaque is a tough fatty substance that can build up on the inside walls of the arteries. Eventually the vessels can get so clogged that blood does not flow normally, and the result can be a heart attack or stroke, both of which are serious and sometimes fatal. The traditional method for removing the plaque involves opening the chest and making several incisions, a long and sometimes risky operation. It is also expensive and requires weeks for recovery.
An effective alternative is to use a laser beam to burn away the plaque. The key to making this work is the doctor's ability to see inside the artery and direct the beam, another area in which fiber optics and lasers are combined into a modern wonder tool. An optic fiber that has been connected to a tiny television camera can be inserted into an artery. These elements now become a miniature sensor that allows the doctor and nurses to see inside the artery while a second fiber is inserted to carry the bursts of light that will burn away the plaque.
The technique works in the following way. The fiber-optic array is inserted into a blood vessel in an arm or leg and moved slowly into the area of the heart and blocked arteries. When the array is in place the laser is fired and the plaque destroyed, and then the exhaust vapors are sucked back through a tiny hollow tube that is inserted along with the optical fibers. When the artery has been cleaned out the doctor removes the fibers and tube, and the operation is finished. This medical process is known as laser angioplasty. It has several obvious advantages. First, no incision is needed (except for the small one in the vessel to insert the fibers). There is also little or no bleeding, and the patient can enjoy total recovery in a day or two.
Laser angioplasty does have some potential risks that must be considered. First, when the laser beam fires at the plaque it must be aimed very carefully because a slight miss could cut through the wall of the artery and cause serious bleeding. The patient's chest would then have to be opened up after all. Another problem involves small pieces of burnt debris from the destroyed plaque. If these enter the bloodstream, they can cause blockage in smaller blood vessels, bringing further complications. Fortunately, continuous technical advancements have considerably reduced these risks, and the number of successful laser angioplasties performed is increasing each year.
Lasers Heal and Reshape the Eyes
Some of the most remarkable breakthroughs for medical lasers have been in the area of ophthalmology, the study of the structure and diseases of the eye. One reason that laser beams are so useful in treating the eye is that the cornea, the coating that covers the eyeball and admits light into the interior of the eye, is transparent. Since it is designed to admit ordinary light, the cornea lets in laser light just as well and remains unaffected by the beam.
First, the laser is very useful in removing extraneous blood vessels that can form on the retina—the thin, light-sensitive membrane at the back of the eyeball. It is on the retina that the images of the things the eye sees are formed. Damage to the retina can sometimes cause blindness, the most common form in the United States resulting from diabetes (a disease characterized by high levels of blood sugar) when, in some advanced cases, hundreds of tiny extra blood vessels form on the retina. These block light from the surface of the membrane, resulting in partial or total blindness.
The laser most often used in the treatment of this condition is powered by a medium of argon gas. The doctor aims the beam through the cornea and burns away the tangle of blood vessels covering the retina. The procedure takes only a few minutes and can be done in the doctor's office. The laser can also repair a detached retina—one that has broken loose from the rear part of the eyeball. Before the advent of lasers detached retinas had to be repaired by hand, and because the retina is so delicate this was a very difficult operation to perform. Using the argon laser, the doctor can actually "weld" the torn retina back in place. It is perhaps a strange coincidence that Gordon Gould, one of the original inventors of the laser, later had one of his own retinas repaired this way.
Another condition that affects the eye is glaucoma, which is characterized by the buildup of fluid in the eye. Normally the eye's natural fluids drain away a little at a time, and the eye stays healthy. In eyes impaired with glaucoma the fluid does not drain properly, and the buildup affects vision; blindness can sometimes result. In some cases drugs can be used to treat glaucoma. If the drugs fail, however, many doctors now turn to the laser to avoid conventional surgery. The laser punches a hole in a preplanned spot and the fluid drains out through the hole. Again, the treatment can be performed in a doctor's office instead of a hospital.
Using Lasers for Eye Surgery
The laser works like a sewing machine to repair a detached retina, the membrane that lines the interior of the eye. The laser beam is adjusted so that it can pass harmlessly through the lens and focus on tiny spots around the damaged area of the retina. When it is focused, the beam has the intensity to "weld" or seal the detached area of the retina back against the wall of the eyeball.
[Image not available for copyright reasons]
Perhaps most exciting of all the eye-related laser applications is the reshaping of the eye's cornea, a technique widely known as LASIK (which stands for Laser-Assisted In Situ Keratomilensis). As Breck Hitz describes it,
The patient's eyeglass prescription is literally carved inside the cornea with the beam of an excimer laser [a laser device that produces pulses of ultraviolet, or UV, light]. A small flap of the cornea is first removed with a precision knife . . . and an inner portion of the cornea is exposed to the excimer laser. After the prescription is carved, the corneal flap that was opened is then put back into place over the ablated [surgically altered] cornea.6
LASIK does not come without risks. The changes it makes in the cornea are permanent, and the danger of unexpected damage is ever present. However, the procedure has become increasingly popular each year; about a million Americans had it done in the year 2000, and about four thousand surgeons in the United States were trained to perform it.
Some Cosmetic Uses of Lasers
Medical lasers are also widely used for various types of cosmetic surgery, including the removal of certain kinds of birthmarks. Port-wine stains, reddish purple skin blotches that appear on about three out of every one thousand children, are an example. Such stains can mark any part of the body but are most commonly found on the face and neck.
The medical laser is able to remove a port-wine stain for the same reason that a military laser is able to flash a message to a submerged submarine. Both lasers take advantage of the monochromatic quality of laser light, that is, its ability to shine in one specific color. The stain is made up of thousands of tiny malformed blood vessels that have a definite reddish purple color. This color very strongly absorbs a certain shade of green light. In fact, that is why the stain looks red. It absorbs the green and other colors in white light but reflects the red back to people's eyes.
To treat the stain, the doctor runs a wide low-power beam of green light across the discolored area. The mass of blood vessels in the stain absorbs the energetic laser light and becomes so hot that it is actually burned away. The surrounding skin is a different color than the stain, so that skin absorbs only small amounts of the beam and remains unburned. (Of course, the burned areas must heal, and during this process some minor scarring sometimes occurs.)
A similar method is often successful in removing tattoos. A tattoo is formed when very strong dyes are injected with needles into a person's skin. Someone who has been tattooed may decide later in life that he or she does not want the tattoo anymore; and in the past, the only way to remove these designs involved surgery or burning off the tattoo with acid. Luckily, the laser offers an alternative to such extreme measures. The beam bleaches the dyes in the tattoo without burning the surrounding skin. (As in the case of port-wine stains, some light scarring is possible.)
Still another example of a laser-assisted cosmetic procedure is the removal of unwanted hair. "The laser emits a gentle beam of light," explains Chicago cosmetic surgeon Jeffrey Melton,
which only is absorbed in the hair follicle (leaving the skin unharmed). The laser delivers energy which is absorbed in the hair and transformed to heat. The heat destroys the hair follicle within a small fraction of a second. . . . Laser hair removal is good for both facial hair removal and for body hair removal. . . . Perhaps the most commonly treated areas are facial hair in women.7
Dentistry is another branch of medicine that has benefited tremendously from laser technology. Indeed, lasers have made some people stop dreading a visit to the dentist. No one enjoys having a cavity drilled, of course. It usually requires an anesthetic (a painkiller like novocaine) that causes uncomfortable numbness in the mouth; also, the sound of the drill can be irritating or even sickening to some people.
Many dentists now employ an Nd-YAG laser (which uses a crystal for its lasing medium) instead of a drill for most cavities. The laser treatment takes advantage of the simple fact that the material that forms in a cavity is much softer than the enamel (the hard part of a tooth). The laser is set at a power that is just strong enough to eliminate the decayed tissue but not strong enough to harm the enamel. When treating a very deep cavity bleeding sometimes occurs, and the laser beam often seals off blood vessels and stops the bleeding.
The most often asked question about treating cavities with lasers is: Does it hurt? The answer is no. Each burst of laser light from a dental laser lasts only thirty-trillionths of a second, much faster than the amount of time a nerve takes to trigger pain. In other words, the beam would have to last 100 million times longer in order to cause any discomfort. So this sort of treatment requires no anesthetic.
There are literally hundreds of other medical uses for the laser. Still, numerous medical conditions cannot be helped by laser light. And even in those that do respond to laser treatments, a doctor may have a good reason for choosing a different method in a specific case. The plain fact is that, while the laser is a marvelous medical tool, it cannot cure every ill. Yet the world has seen probably only a small fraction of the laser's potential. After all, this supertool has only existed since 1960, and, considering the medical advances it already has created, the future appears promising indeed.
Advantages of Lasers for Dental Surgery
In this excerpt from an article in The Dental Clinics of North America Robert A. Strauss of the Medical College of Virginia mentions some of the advantages of using lasers for oral surgery.
Decreased post-operative swelling is characteristic of laser use [for oral surgery]. Decreased swelling allows for increased safety when performing surgery within the airway [the mouth] . . . and increases the range of surgery that oral surgeons can perform safely without fear of airway compromise. This effect allows the surgeon to perform many procedures in an office or outpatient facility that previously would have required hospitalization. . . . Tissue healing and scarring are also improved with the use of the laser. . . . Laser wounds generally heal with minimal scar formation and . . . often can be left unsutured [without stitches], another distinct advantage.