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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.
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