Lasers Beginning to Solve Vision Problems

by Food and Drug Administration (FDA)

Although it happened more than a year ago, 68-year-old Ervin Chudnow of West Palm Beach, Fla., still marvels at how a laser gave him back good eyesight.

Several years after having a cataract removed from his left eye, Chudnow began having problems with hazy vision. "It was like looking through a window with soap on it," he says. His sight became so poor he had difficulty with daily tasks such as driving and reading the paper.

Chudnow went to see his ophthalmologist, who used about a dozen one-billionth-of-a-second blasts of infrared laser light to puncture the clouded membrane lining the back of the lens of his eye that was obscuring his vision.

"I went in there nearly blind in one eye, and after the half-hour walk home, I could see perfectly again," Chudnow recalls.

Many people tell dramatic tales of how lasers restored their sight. A versatile tool, lasers are commonly used to treat a variety of eye disorders such as retinal tears and glaucoma. In the not-too-distant future, moreover, a few zaps of laser light might bring back 20/20 vision to those who are nearsighted, farsighted, or have problems with astigmatism.

"Someday lasers may be routinely used to treat most things wrong with the eye," says Richard Weiblinger, a senior scientist in the Food and Drug Administration's ophthalmic devices division.

FDA's Center for Devices and Radiological Health regulates medical lasers to ensure they are safe and effective. Although surgical lasers must comply with stringent FDA safety standards, like any other surgical procedure, laser eye surgery is not completely without risk.

A laser (an acronym for "light amplification by stimulated emission of radiation") is a simple device that usually combines electricity, a series of mirrors, and a crystal or gas to generate an extremely intense and narrow beam of a single type of light, such as infrared or ultraviolet. (Sunlight, in contrast, is composed of a jumble of different colors, spread out in different directions.)

The laser's usefulness in ophthalmology stems from the precision and ease with which it can be used to reach tissues deep within the eye. Unlike the smallest scalpel used in surgery, which makes cuts as wide as the tip of a pin and crushes neighboring tissue, a "laser scalpel" can slice as thin as the width of a cell without damaging surrounding cells. This precision allows eye doctors to target diseased blood vessels, for example, while sparing healthy ones, and fosters a speedy recovery with little resulting scar tissue.

Even minor amounts of scar tissue can pose major impediments to sight by blocking the pathway of light entering the eye. That pathway is what makes the laser so useful in treating patients with eye disorders; the pupil acts as a natural window through which laser beams can enter to mend tissues deep within the eye. Because the ophthalmologist doesn't have to cut open the eye during laser surgery, there are fewer risks of infection and less pain than with standard surgery. Laser surgery can be done in an ophthalmologist's office or hospital outpatient department, so it also is less expensive.

Membranes of the Eye

Approximately half of all patients who have cataract surgery need the type of laser surgery Chudnow had. A cataract is a clouding of the normally clear and transparent lens of the eye. (See "Lifting the Clouds of Cataracts" in the December 1989-January 1990 issue of FDA Consumer.)

During cataract surgery, an ophthalmologist often replaces the natural lens of the eye with an artificial one. Several months later, however, the membrane in the back of the eye, which surrounds and supports the lens, may become cloudy, impairing vision.

Ophthalmologists counter this problem by using the intense infrared light of a neodymium: yttrium aluminum garnet (Nd:YAG) laser to create an opening in the membrane. During this procedure, called a posterior capsulotomy, each flash of the laser causes a microscopic explosion in the membrane. The mini-explosion is thought to vaporize cells.

Although the laser beam travels through other eye tissues before it reaches the membrane, it doesn't harm these tissues because only the highly focused tip of the beam has enough energy to cause a microexplosion. This tip touches only the membrane in the back of the eye, which has no nerve endings. Posterior capsulotomies, consequently, are painless. This quick procedure rarely has any serious complications.

Glaucoma

An Nd:YAG laser is also used to treat some cases of glaucoma. This disease, which affects at least two out of every 100 Americans over 35, according to the American Academy of Ophthalmology, is one of the leading causes of blindness in this country. (Earlier this year, President Bush was diagnosed as having a type of glaucoma.)

The hallmark of glaucoma is an excessive build-up of fluid pressure in the eye. The unhealthy pressure is caused by a blockage of the canals through which the clear inner eye fluid continuously flows. If left untreated, glaucoma eventually damages the sight (optic) nerve.

An Nd:YAG laser can relieve the fluid pressure by creating an opening, allowing the eye fluid to drain properly. Although a slight risk of bleeding accompanies this type of laser surgery, it rarely causes serious problems.

Macular Degeneration

A different type of laser — the argon laser — is used to treat some patients with the more severe form of an eye disorder called macular degeneration. Although this disease doesn't cause total blindness, it is a leading cause of loss of both central and reading, vision. Macular degeneration is particularly common in people over 65.

The macula is the portion of the light-sensing retina (see diagram) that light rays strike to provide the sharp, straight-ahead vision needed for driving and reading small print. In the less common but more severe form of macular degeneration, for no known reason, new blood vessels grow beneath the macula. These abnormal vessels leak fluid and blood, destroying nearby macula cells. If the leakage and bleeding continue, much of the macula may be damaged irreparably within a few weeks or months. The resulting dense scar tissue blocks out central vision, much like an opaque smudge does in the center of one's glasses.

With early detection, severe vision loss from this type of macular degeneration can usually be prevented with argon laser treatment. This relatively low-energy laser heats, rather than vaporizes, tissues, acting essentially like a welder. A study conducted by the National Eye Institute showed that argon laser treatment can slash by more than half the chances of experiencing severe vision loss from macular degeneration.

About the Author

www.fda.gov
FDA is A United States government body that oversees medical devices, including contact lenses, intraocular lenses, excimer lasers and eyedrops. In the US, these products must be approved by the FDA before they can be marketed.