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Is RK Safe and Effective?
"FDA does not regulate radial keratotomy
because it is a medical procedure, not a
medical device," says Emma Knight, an
ophthalmologist and medical reviewer with
FDA's Center for Devices and Radiological
Health. "The knife used in RK had been
cleared by the agency for general corneal
surgery."
The National Eye Institute (NEI), however,
concluded from a 10-year study called
"Prospective Evaluation of Radial Keratotomy
(PERK)" that RK is "reasonably safe and
effective … with serious
complications being rare."
All patients in the study had -2 to -8
diopters and could be corrected to 20/20
vision or better with glasses or contact
lenses. (A diopter is the unit of
measurement of spectacle or contact lens
power. A minus value indicates
nearsightedness; plus indicates
farsightedness, or hyperopia. Euley's
correction was -3.25 diopters.)
Results of the NEI-sponsored multicenter
trial were reported by study investigator
George Waring III, M.D., and colleagues in
the October 1994 Archives of Ophthalmology.
Among 374 patients (with 693 operated eyes)
who returned for the 10-year follow-up:
70 percent said they did not wear glasses or
contact lenses for distance vision.
53 percent had 20/20 vision without glasses.
85 percent had at least 20/40 vision without
glasses--the acuity most states require for
driving without glasses.
Of the total 793 eyes operated (including
data from the most recent examination of
those who didn't return for the 10-year
follow-up), 143 lost one line of best
spectacle-corrected vision on the standard
eye chart, 19 lost two lines, and four lost
three lines. (Best corrected vision in all
but 16 eyes was 20/20--they previously had
better than 20/20 corrected vision. Thirteen
eyes were corrected to 20/25 and three to
20/30.) This means that, although eyesight
without glasses was improved from
pre-surgery acuity, residual nearsightedness
could not be corrected with glasses to
pre-surgery acuity.
38 percent of patients were corrected within
one-half diopter of the predicted result; 60
percent were within 1 diopter.
43 percent developed "hyperopic shift"--a
gradual change toward farsightedness (1 or
more diopters between 6 months and 10 years)
at a younger age than would be expected.
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.
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