Surgeons sculpt imperfect eyes Techniques: Making cuts with a laser has usually proved effective in correcting nearsightedness.

September 20, 1998|By Jonathan Bor | Jonathan Bor,SUN STAFF

In the 1970s, Americans blanched at the first reports of a Russian doctor who was curing nearsightedness by cutting tiny slits in the cornea. Now, more than 7,000 Americans each week are tossing their glasses after having their eyes sculpted with lasers.

The boom in refractive surgery has become so intense that ophthalmologists talk with some satisfaction about "the number of eyes" they have corrected each week, month or year.

"Now, I do about 100 eyes in a week," said Dr. Anthony J. Kameen, refractive surgeon at the Greater Baltimore Medical Center. "In July, I did close to 500 eyes. We're expecting that to double in the next year."

Surgical techniques are safer and more precise than ever, thanks to innovations that are proceeding at a dizzying clip. Through it all, the goal has not changed - to bring sharper focus by changing the shape of the eye.

People are nearsighted when their eyes are too long from front to back.

The Russian surgeon S.N. Fyodorov addressed this with a method called radial keratotomy, in which he made a series of cuts in the cornea - the clear, thin tissue that forms a protective layer over the eye. The cuts radiated out from the center of the cornea like spokes on a wheel. As they healed, the cornea contracted and the person's ability to see long distances improved.

Severe corrections called for longer slits - and more of them. Milder corrections called for shorter cuts, and fewer.

Radial keratotomy peaked in the mid-1990s, when close to 300,000 eyes in the United States were being "done" each year. But the technique had limits. First, it could take three months for the eyes to feel comfortable and for vision to stabilize. Second, surgeons had a hard time controlling the degree to which the eye contracted - making the "fix" a disturbingly inexact one.

Luckily, the rapid development of laser procedures guaranteed to make radial keratotomy a historical curiosity. "In 1994 and 1995, RK really fell off the table, and now, only about 10,000 of them are being done a year," said Irving Arons, a Massachusetts consultant who has worked with the laser industry.

In the first laser technique, called photorefractive keratectomy (PRK), surgeons use a laser to vaporize cells on the cornea's surface. In a more advanced technique, called LASIK (for laser-assisted in-situ keratomileusis), surgeons peel back the outer layer of the cornea, vaporize underlying cells, and then restore the flap to its original position.

This year, surgeons will treat an estimated 258,000 eyes with LASIK and 110,000 with PRK, says Arons.

LASIK is, to say the least, a marvel of technology.

The patient, calmed with a tranquilizer, lies on a table beneath a thick, metal arm that holds the laser. The surgeon applies anesthetic drops to the eye, then holds the eyelid open with a ring called a speculum. Next, the surgeon places a second ring against the eye and applies suction through its center. This draws the eyeball outward and immobilizes it.

Now, a tiny slicing device called a microkeratome is used to cut the flap. Working like a tiny meat slicer placed on its side, it rides across a track on the suction ring.

"An automated gear system drives it across," said Dr. Terrence P. O'Brien, a refractive surgeon with the Johns Hopkins Wilmer Eye Institute. "It cuts very smooth - not like shaving by hand."

The flap is thinner than a hair, its thickness determined by the distance the eyeball is pulled toward the cutter. The surgeon makes sure the eye is correctly positioned by measuring the pressure within the eye - pressure that will rise or fall depending on how much the eye is distended.

With tweezers, the surgeon peels the flap back, exposing the inner layer of cornea.

The laser is called into action. Clicking gently, it emits brief pulses of cool ultraviolet radiation that vaporizes cells. Each pulse takes off a quarter micron of tissue. On average procedure, the surgeon takes off 30 to 40 microns - about 5 percent the thickness of the cornea.

Before each procedure, the machine is told how much tissue to cut - and where - by means of a plastic card that, in effect, contains the patient's prescription. (Surgeons use the laser to correct nearsightedness and astigmatism, a focusing problem created by irregularities in the curvature of the eye. Like an old basketball, the astigmatic eye is slightly "out of round.")

The laser clicks away for 20 to 30 seconds in most cases - up to two minutes in the most severe cases. "If the patient decides to move, or sneezes, I lift my foot off the petal and we stop and refocus," said Kameen.

Once the sculpting is done, the surgeon restores the flap and smooths it with a tiny rod. The operation is done - lasting no more than 10 minutes.

"With LASIK, people we do today are back to work tomorrow," Kameen said. The recovery is generally pain-free, though patients can experience dryness for a week or two.

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