Lasers Beginning to Solve Vision Problems : Part 2

by Food and Drug Administration (FDA)

(Page 2 of 2)

The green beams of the argon laser are only absorbed by red objects, so it selectively heats up and seals blood vessels (because they contain red blood cells) and leaves most other parts of the eye undisturbed. The narrowness of the beam enhances laser precision, allowing the ophthalmologist to target only diseased blood vessels.

This type of surgery generally takes only a few minutes and may be done with the aid of a local anesthetic to prevent discomfort. Soon afterwards, the patient is able to return home and resume normal daily activities.

A fungal disease called ocular histoplasmosis can cause faulty blood vessels to grow and damage the macula. This is a significant cause of vision loss in the southeast and midwest United States, where this particular fungus is prevalent. Experts estimate that laser treatment of the abnormal vessels can prevent up to 2,000 cases of serious vision loss due to the disease each year if treatment is given early, before extensive damage has occurred.

Diabetic Retinopathy

Ophthalmologists use a similar procedure to seal off leaky blood vessels or destroy diseased tissue in the retinas of patients with diabetic retinopathy, another leading cause of blindness. The hallmark of this disease is faulty blood vessels on or within the retina. These vessels bleed, scarring the retina. According to the National Eye Institute, nearly half of all diabetics have at least mild diabetic retinopathy. If used in early stages of the disease, laser treatment often halts the patient's loss of vision and sometimes even reverses it. The procedure is usually painless and without complications.

Retinal Tears

An argon or another type of tissue-heating laser called a krypton laser is also used to spot-weld retinal tears. These horseshoe-shaped holes in the retina may open small blood vessels and cause bleeding into the central cavity of the eye. Often caused by a blow to the head, retinal tears can cause flashes of color or black spots to appear in one's line of sight.

Laser Sculpting

Still experimental is the use of the laser on the eye's surface to treat people for nearsightedness, farsightedness or astigmatism.

When light rays enter the normal eye, they are bent by the transparent front covering of the eye (cornea) and the lens so that they are brought to a single, sharp focus on the retina. But in the nearly one-third of Americans who are nearsighted (have trouble seeing distant objects), the light rays bouncing off faraway objects come to focus in front of — instead of directly on — the retina. This happens because either the curve of the lens or cornea is too steep or the eye is too long. In farsightedness (trouble seeing objects close up), the eye is too short or the curve of the cornea or lens is not steep enough. The rays, consequently, merge in back of the retina. The end result in both conditions is blurred vision.

To counter these vision flaws, most nearsighted or farsighted individuals wear glasses or contact lenses shaped to bend the light rays so that they properly reach the retina. By precisely reshaping the cornea with the laser, ophthalmologists hope to achieve the same effect. Theoretically, once the laser surgery is done, the person could throw away the no-longer-needed glasses.

Nearsightedness

Corneal surgery to cure nearsightedness has been attempted with traditional surgical tools, but without reliable results. In this procedure, called a radial keratotomy, an ophthalmologist uses a scalpel to cut several small slits in the cornea. These slits slightly flatten the cornea by changing the pressure in the eye and weakening the cornea's structure.

But nearly half of all the eyes treated with this procedure are either undercorrected or overcorrected, according to a study published in the Feb. 22, 1990, Journal of the American Medical Association. Apparently, the surgery often fails because the depth and shape of cuts made by the hand-held scalpel are inconsistent, or because scar tissue alters the desired contour of the cornea.

When an ultraviolet excimer laser is used, however, preliminary studies show that exact uniform tissue removal cuts can be accomplished with minimum scarring. The high energy of this laser beam ejects cell-sized fragments from the surface of the cornea. Such precision has enabled several research groups to directly remove minute quantities of tissue from the center of the cornea to flatten it, thus restoring sharp vision. Investigators hope to use the excimer laser on farsighted individuals, in whom the curve of the cornea is steepened rather than flattened.

Researchers speculate that because the excimer laser damages such small amounts of tissue, it "fools the eye into not knowing it's been traumatized," says Weiblinger. "Once the body knows it's been invaded, it tries to heal itself. That healing process can alter the desired recontouring of the eye."

The total sculpting procedure with the excimer laser takes less than a minute to complete, although about 20 minutes are needed beforehand to train patients to keep their eyes steady. The cornea may ache for about a day following surgery, and patients need to wear an eye patch for one or two days.

Initial results of laser sculpting by researchers at Louisiana State University Eye Center in New Orleans and Johns Hopkins University in Baltimore are encouraging. These investigators were able to improve one patient's 20/300 eyesight to 20/40 eight weeks after treatment. Another woman, whose nearsighted eye was corrected nearly two years ago, still sees perfectly without glasses or contact lenses. More extensive and longer-term testing will have to be done, however, to ensure the safety and effectiveness of laser sculpting for nearsightedness.

Astigmatism

The excimer laser is also being used experimentally to correct astigmatism. This blurred vision is caused by bumps and pits on the corneal surface, which prevent light rays entering the eye from merging into a single, sharp focus. Preliminary tests on more than 50 patients in Berlin, Germany, indicate that a series of T-shaped incisions made by the laser may be effective in smoothing out corneal irregularities. Various researchers in the United States are trying the same procedure on persons with astigmatism, but have not yet reported results.

If more extensive tests show laser sculpting is a safe and effective method for correcting near- or farsightedness or astigmatism and it becomes an accepted practice, various laser companies estimate the procedure will probably cost between $1,000 to $2,000 per eye.

Even if laser sculpting continues to show promise in clinical trials, however, it will be several years before a patient will be able to enter the ophthalmologist's office wearing glasses, get a few zaps of laser light, and achieve perfect vision after a few weeks. Though today it's hard to imagine such a scenario, several years ago it would have been just as hard to believe the quick and easy laser surgery Chudnow had would one day be possible.

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.