Laser’s Medical Uses Vary With Wavelength
Luke Skywalker used one and President Reagan would love to, as well.
But long before lasers were tapped for Star Wars, they were assigned more mundane tasks: cutting and welding steel, etching plastic, and even vaporizing human tissue in the operating room.
Physicians’ use of lasers--the name is actually an acronym for Light Amplification by Stimulated Emission of Radiation--dates back to 1962 when researchers finally came up with a medical application for the device that engineers at Hughes Aircraft Co. had invented two years earlier for the Pentagon.
Eye problems were the first to be attacked with the new device. Researchers discovered that a detached retina could be welded back onto the rear of the eye far more easily with a laser than with the then-standard white light.
Evolution of Use
Later, the same device was used to destroy the masses of blood vessels that often accumulate behind the eyes of diabetics, a procedure that is still the most popular use of the medical laser, according to Michael Berns, director of the Beckman Laser Institute at UCI.
Over the next two decades, researchers discovered that the laser could be used for scores more procedures, from erasing birthmarks to opening blocked Fallopian tubes, to vaporizing cancerous tumors.
The applications depend on the “active medium,” a fancy word for the chemical used to power the laser. Current favorites are argon, carbon dioxide, krypton and yttrium-aluminum-garnet, generally called YAG, and the closely related neodymium yttrium-aluminum-garnet, or Nd: YAG.
The actual laser beam is created by introducing energy into a cylinder that has been filled with the chosen “active medium” and sealed at both ends with mirrors. As the light beam bounces off the mirrors, it is amplified into an intense beam with a wavelength determined by the medium used to produce it.
Blue-Green for the Eye
It is this wavelength that determines whether the light will weld, make a superficial burn or blow a hole through human tissue. And it is the laser’s wavelength that determines its potential applications.
For example, for welding a detached retina, physicians typically use an argon gas laser because it emits a blue-green light wave that harmlessly passes through the clear liquid of the eye before being absorbed by the bloody red tissue of the retina.
To heal deep internal bleeding, such as ulcers, physicians use lasers powered by yttrium-aluminum-garnet (YAG) crystal because its wavelength allows the light to coagulate masses of directly exposed bloody tissue.
And to vaporize intestinal polyps or a brain tumor, the intense power of the invisible infrared of a carbon dioxide laser beam is preferred because it can explosively burn tissue under its beam without harming nearby material.
