Erasing skin marks with lasers - includes related article on medical use of lasers - Cover Story

FDA Consumer, March, 1992 by Ricki Lewis

About 5 percent of the nation's 10,000 plastic surgeons use lasers, says Noe.

FDA regulates lasers, including those for medical uses. "FDA evaluation is of the device itself We try to find out if the device to be marketed is equivalent to another device on the market. It does not have to be superior. We look at safety and efficacy," says Sankar Basu, Ph.D., a physicist with FDA's surgical devices evaluation branch.

The radiation a laser emits depends on the chemical through which it passes. A carbon dioxide (CO[.sub.2]) laser, for example, emits energy that can heat water; it can vaporize watery tissue near the body's surface. In dermatology, CO[.sub.2] lasers are used to remove warts, lip lesions, and ingrown toenails. CO[.sub.2] lasers, however, have no effect on blood, which permeates tissue beneath the skin's outer layer.

The blue-green emission of an argon laser is suited for tissue with a lush blood supply. It passes right through watery tissue, but is absorbed by hemoglobin, the vibrant red protein in red blood cells that carries oxygen to the body's tissues. In a port-wine stain, hemoglobin courses through the abnormally numerous blood vessels in the underlying skin layer. An argon laser can destroy these extra vessels, lightening the marks in 80 percent of adult cases. But a child's delicate skin can be badly scarred by the powerful argon laser.

A gentler laser for benign skin conditions is a flashlamp-pumped pulsed dye aser, which FDA cleared for use in 1987. The device consists of a dye (rhodamine in methanol) that is excited by high-intensity flashlamps to release photons, which are tiny subatomic packets of light energy. Like an argon laser, the wavelength of the pulsed dye laser is absorbed by hemoglobin, but it is less powerful. When aimed at the skin, a few brief pulses safely zap away the blood vessels. The trick is to apply the light pulses faster than the blood vessels can dissipate the heat. A pulse of this laser takes 360 to 450 microseconds, and the blood vessels need about 3 milliseconds (equal to 3,000 microseconds) to recover. In contrast, an argon laser pulse typically takes five-hundredths of a second, long enough to damage much more than the stain, and thereby cause a scar to form.

The ability of the flashlamp-pumped pulsed dye laser to treat port-wine stains was first reported in the Feb. 16, 1989, New England Journal of medicine by Oon Tian Tan, M.D., and colleagues, of the Boston University Medical Center. Since then, other studies have confirmed their findings--and some 60,000 persons have had their birthmarks removed worldwide, according to the Candela Laser Corp. in Wayland, Mass., which markets the device and keeps track of its use.

--R.L.