A Lighter, Defter Touch
Years of refinement have made laser eye surgery better than ever
To understand how laser eye surgery works, it helps to know how nearsightedness and farsightedness typically occur and how the surgery corrects them. In someone with normal vision, light rays of an image pass through the cornea and the lens behind it and focus directly on the retina, producing a clear image. This nerve-sensitive tissue at the back of the eye converts the image into electrical impulses that travel along the optic nerve to the brain. If someone's eyeball is too long, however, the light rays focus in front of the retina and, if too short, on a point behind it. The surgeon can't change the actual shape of a person's eyeball. However, using a computer-controlled ultraviolet beam of light called an excimer laser, he or she can reshape the cornea, the eye's principal focusing mechanism, to improve visual acuity. (Laser eye surgery can also correct astigmatism, a blurriness that typically occurs when the surface of the cornea is uneven.)
Fool the eye. Refractive surgeons, who generally correct people's vision by changing how light rays "refract," or bend in the eye, discovered that by working inside the eye, as they do with LASIK, they could fool it into not recognizing that it had been wounded by the laser. After surgery, the eye didn't feel painful, since pain is a response to wound healing. And because the eye's surface hadn't been interfered with, vision recovery was immediate. Similarly, LASIK sidestepped a problem that plagued early PRK procedures: A patient's vision was sometimes clouded by a whitish haze caused by scarlike tissue that developed after the surgery. "You've given the eye a loud message that there's been an injury, and the eye will respond with healing," says Richard Foulkes, an adjunct professor of ophthalmology at the University of Illinois, who performed the surgery on Duong. "Too vigorous healing would cause hazing."
Thanks to an antibiotic eyedrop called mitomycin C, the hazing problem has been almost eliminated in the past five years and with it one of the major downsides to PRK. And the use of contact lenses to act as bandages to protect the eyes during the first several days following surgery makes recovery from PRK less painful. At the same time, surgeons have discovered that LASIK isn't necessarily the miracle cure for bad eyesight that it originally appeared to be. For one thing, although a patient's vision is initially better with LASIK, as the weeks and months pass, studies indicate that people who've had PRK may achieve a slight edge in improved eyesight. Dry-eye problems, the No. 1 complication of laser eye surgery, also tend to occur more frequently with LASIK since the surgery cuts into the cornea and severs some of the corneal nerves that stimulate tears.
Finally, there's the flap itself. Most flaps are cut with a mechanical blade called a microkeratome. If the flap is too thick or too thin or cuts an uneven plane, it can affect the outcome of the surgery. The flap could wrinkle or not reseal itself properly. And in some patients, cutting a flap carries a slight risk of structurally weakening the cornea itself, which can lead to a very serious condition called ectasia, in which the cornea bulges out. Although many early laser eye surgery problems have been resolved in the more than 10 years that the procedure has been performed, those that remain are almost always related to the flap, says Marguerite McDonald, a clinical professor of ophthalmology at Tulane University Health Sciences Center. Word to the wise: "You can't have problems with the flap if you don't have one," she says.
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