Eye Surgery Helps Some See Better : Part 2

by Food and Drug Administration (FDA)

(Page 2 of 3)

The cornea is weakened by radial keratotomy, increasing the risk of eye rupture from physical trauma. According to the article by the American Academy of Ophthalmology, however, there have been reports of severe eye trauma without damage to the incision wounds. The report also says that potentially blinding complications, such as corneal infection or perforation are rare.

More recent studies using newer RK techniques have achieved better optical results, says Peter Hersh, M.D., director of keratorefractive surgery at Montefiore Hospital, Bronx, N.Y.

Surgeons have designed improved methods for calculating the number and length of incisions and the diameter of the optical zone (the central clear zone that has no cuts) that will produce the best results in a given patient, he says.

"We've had numbers reported as high as 95 percent or so for 20/40 as the procedure has evolved," Hersh says. "The most important variable is patient age. Younger patients tend to heal their incisions better and more quickly, and therefore get less of an effect. Also, patients with lower degrees of myopia do better than high myopes," he says. Some other factors that may be considered when determining surgical procedure include corneal curvature, topography and thickness, and ocular pressure.

The Laser Method

An alternative to radial keratotomy is photorefractive keratectomy, or PRK. "In countries where PRK has been available for some time, the procedure has largely replaced RK as the procedure of choice," says FDA's Knight, adding that "with FDA approval of the excimer laser, this trend is expected to follow in the United States."

In this procedure, the surgeon operates an excimer laser programmed to deliver bursts of ultraviolet light that vaporize precisely targeted corneal tissue. The effect, as in RK, is to flatten the cornea. Also like RK, PRK takes about 15 minutes and is done under topical anesthesia.

In October 1994, FDA's ophthalmic devices advisory panel recommended conditional approval of one manufacturer's excimer laser for refractive surgery, pending reformatting and reanalysis of some of the data.

"This was the first time the agency critically assessed safety and effectiveness data of any device for refractive surgery," says Knight, "and the meeting was long and full of debate."

Approval in October 1995 was based on PRK results in about 1,600 healthy myopic eyes. In most eyes, the corneal surface healed in three days, and vision took at least three months to stabilize. Most patients studied were corrected to 20/20 vision or better with glasses or contact lenses before surgery. Best corrected vision was worse in 6 percent of patients after surgery but, of those, only 1 percent had less than 20/25 acuity and fewer than 0.2 percent were worse than 20/40.

In 95 percent of eyes, vision without glasses was corrected to 20/40 or better; 65 percent achieved 20/20 or better. About 5 percent of patients continued to need glasses all the time for distance, and up to 15 percent needed glasses occasionally, such as for driving. Results were best in younger patients with lower degrees of myopia.

Some 63 percent of patients had mild corneal haze after surgery, and 10 percent experienced mild glare and halos around lights. These conditions diminished or disappeared in most patients in six months.

According to the American Academy of Ophthalmology, RK results are best in patients with low to moderate nearsightedness and generally is not recommended for people with a correction higher than -5 diopters. PRK is effective for patients with higher myopia as well, and is approved for treatment of up to -7 diopters.

With approval of the laser, FDA also reviewed and approved a physician training program and a patient information booklet. The training program for surgeons covers operation and calibration of the laser, plus extensive clinical, didactic and practical sessions. The patient booklet is provided to physicians, who in turn are required to give it to patients and discuss it with them before surgery.

Mary Taylor had her first PRK in November 1993. The highly myopic 42-year-old Winchester, Va., woman had worn glasses since second grade. Her correction was -9.5 diopters in one eye and -10 in the other.

"I tried contacts a few times, but never really got comfortable with them," she says, "and, although I didn't especially mind wearing glasses, I was bothered by how helpless I felt without them. The thought of losing them if something happened while I was driving or swimming — even if I had a spare pair — was always a worry in the back of my mind."

Taylor says she received about 700 laser bursts at periodic intervals during the procedure. Then the doctor put a soft "bandage" contact lens in her eye to be worn the next few days until the surface cells healed. She was given a nonsteroidal anti-inflammatory eyedrop for pain and a prescription for additional pain medicine, if needed.

"That first day I felt a mild discomfort, like a residual scratchiness after removing a piece of sand from the eye. It was gone when I woke up the next morning," Taylor says. Although her vision improved greatly immediately, it took about a month or two, she says, before she was seeing 20/20. Six months after the first operation, she returned for surgery in the second eye.

As of October 1994, according to Taylor's doctor, her vision was 20/25 without glasses and 20/20 with glasses, and her correction was -0.75 diopter. Taylor says she still has some trouble with night glare and needs glasses to drive at night, but she's delighted with the results. "For the first time in my life that I could remember, I could see my feet in the shower," she says.

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.