 Re: EPIDEMIC OF CORNEAL WEAKENING AFTER REFRACTIVE SURGERY
>We're just now seeing the long term effects of RK. One would expect
>that other corneal refractive surgical procedures, all of which
>compromise corneal strength and integrity, will have similar long term
>effects.
Certainly the problems of corneal weakening attributed to Radial
Keratotomy (RK) are a warning call, but RK is nothing like current
excimer laser assisted refractive surgery. To make such a comparison
is like comparing a bicycle to a Harley.
For those who don't know, RK is the process of making radial
spoke-like incisions at least 90% through the cornea. A central area
of about 3.0mm remains untouched, although techniques vary. The
incisions cause the cornea to collapse due to weakening. This collapse
provides a central flattening of the cornea and reduction in myopia
(nearsighted, shortsighted) vision.
RK was developed in Japan, but popularized in the Soviet Union where
providing the surgery was significantly less expensive than
manufacturing and distributing spectacles. Remember that in the Soviet
system the government provided everything, so glasses were a
government expense. RK had some moderate success in the US, but never
became anywhere nearly as popular as LASIK.
I do not know of any study to back up my observations, but it appears
from anecdotal information that those who had RK with more than 4
full-length incisions are now developing fluctuation in vision
throughout the day and a shift toward hyperopic (farsighted,
longsighted) vision.
This hyperopic shift experienced by some RK patients is doubly
problematic because many patients with RK are past age 40 and are
developing presbyopia - the inability to focus on objects near. The
combination of hyperopia and presbyopia provides poor vision at almost
all distances. Add to that the fluctuation throughout the day and
there are a lot of unhappy RK campers out there.
While some may compare the now emerging problems of RK as a
bellweather of what will happen with LASIK, they ignore many important
facts. Put simply, LASIK, PRK, LASEK, Epi-LASIK, and IntraLASIK are
nothing like RK.
Even at the time of its popularity, organized ophthalmology was very
strongly split on RK. So split that a group of RK surgeons sued the
American Academy of Ophthalmology because of what they perceived as
anti-RK acts by their own organization.
I just returned from the First International Congress on Corneal
Crosslinking in Zurich Switzerland. Crosslinking is a process to
improve the connections between the long strands of fibrils that make
up the cornea. By increasing the links between the strands, additional
stability is created in the cornea. In the US, Corneal Collagen
Crosslinking with Riboflavin is called C3-R. See
http://www.usaeyes.org/faq/subjects/c3-r.htm
The process of C3-R is remarkably simple. The patient lies down and a
speculum holds open the eye lids. Initially the eyes are soaked for
five minutes with riboflavin (vitamin B2) solution (0.1%
riboflavin-5-phosphate and dextran) until riboflavin is present in the
cornea and anterior chamber.
After the riboflavin has permeated the cornea, a 30 minute application
of UVA light (5.4 J/cm2 at 370 nm) to the central 7 mm of the cornea
is applied. UVA light is combined with reapplication of riboflavin
solution every three minutes
Riboflavin has light energy absorption properties and protects the
iris, lens, and retina from the UVA light.
C3-R, developed by Brian S. Boxer Wachler, MD of Beverly Hills, is
similar to the technique described previously by Wollensak et al
except C3-R does not require removal of the corneal epithelium. The
epithelium is the outermost layer of corneal cells. Because the
epithelium remains intact, the patient does not experience significant
discomfort and vision recovery is immediate.
C3-R has been used to provide corneal stability and even an
improvement from the hyperopic shift for RK patients.
Although very new and needing additional study, C3-R and similar
crosslinking has been performed on more than about 500 eyes in Italy,
Germany, Switzerland, Greece, and the United States.
In addition to RK patients, C3-R has been shown to successfully stop
the progression of keratoconus and refractive surgery induced ectasia.
It has been used with Intacs for advanced cases of keratoconus, and
has been used to strengthen thin corneas to allow PRK to resolve
corneal irregularities.
From the many studies presented at the congress in Zurich, it appears
that C3-R can reliably resolve many issues relating to cornea
instability whether they be caused by natural progression of disease
or induced by refractive surgery..however additional study is
warranted.
Glenn Hagele
Executive Director
USAEyes.org
"Consider and Choose With Confidence"
Email to glenn dot hagele at usaeyes dot org
http://www.USAEyes.org
http://www.ComplicatedEyes.org
I am not a doctor.
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