The cornea is the transparent front part of your eye. Think of it
as similar to the crystal on the front of your watch. The entire
cornea is only about as thick as two business cards, but it has
five different layers.
I'm going to borrow and elaborate on an analogy from Dr. Michael
Doubrava, corneal specialist in Las Vegas, to help us visualize
these layers. Dr. Doubrava, as he spoke to our group in 2004,
brought out a common kitchen sponge, one of those with the
"scratchy" side on the bottom of it. He told us to picture this
sponge as completely transparent.
Here's my elaboration. Add a top layer to the sponge. We must
imagine it is a smooth see-through surface, perhaps like a contact
lens. The next layer under that is transparent and thin, perhaps
like plastic wrap. The next layer (third layer down) is like
the middle of the sponge--but remember, it is transparent. The
fourth layer down is a membrane perhaps like thin plastic wrap, and below that is innermost
layer number five, the thin "scratchy" layer of the sponge, also
transparent. As is the case of the kitchen sponge, this scratchy
layer is the workhorse. And this layer is where our problems
begin when we have Fuchs'. Again, remember this entire cornea is
only as thick as two business cards!
To give these layers their official names, the top (front) layer
is called the epithelium, the second layer back is the Bowman's
Layer (sometimes erroneously called "membrane"), the third and thickest layer is the stroma, the fourth
layer is Descemet's membrane, and finally the thin back layer
(only one cell deep) is called the endothelium. You may view a
diagram of these layers here:
http://www.e-sunbear.com/anatomy_03.html.
I learned the following about the endothelium from a lecture in
June, 2005, by Dr. Henry Edelhauser of Emory University. The
endothelium is an amazing construction formed of hexagonally shaped
cells, tight junctions between the cells, and metabolic enzymes
that work together to control the fluids in the back of the
eyeball from causing a build-up of fluid in the cornea (edema) that fogs up the transparency. To borrow an analogy of Dr. Edelhauser, the cornea needs to be clear like Steuben crystal, but
when too much fluid builds up in the cornea, it can become more
like looking through milk glass. In some few cases the excess
fluid forms blisters (bullae) which can burst and hurt like heck.
What happens in Fuchs' patients is that we have inherited a gene
(so far not identified--but they're working on it) that causes
these hexagonal cells to slowly self-destruct, and they do not
replace themselves. The remaining hexagonal cells slide over to
cover the area left by the cells that failed. Corneal specialists
often can spot this behavior when they use a slit lamp and see
little bumps that look like droplets (called guttata). At this
point the patient may have no visual problems at all, and may
never develop any. But if this cell failure continues and happens
often enough, the hexagonal cells begin to go out of shape, become
irregular, and finally can't do their job of pumping fluid through
the cornea properly.
To quote Dr. Richard Eiferman in Louisville, KY, "The good news
is, we can fix it." He's talking about a corneal transplant.
In a traditional transplant, the surgeon uses a "cookie cutter" to
remove our entire cornea with its one bad and four good layers,
replacing it with an entirely new donor cornea. This requires lots
of stitches. I had a running stitch all around, plus 8 or 12
anchor stitches. This can cause some bumpiness if the donor cornea
doesn't happen to be the exact curvature of our own--hence
astigmatism (multiple vision). Healing time is quite long--up to a
year. (Don't worry about "feeling" the stitches. I still have
nearly all mine in both eyes and have no idea they're there.)
In DLEK and related newer procedures, the surgeon makes a small
incision and removes only the endothelium, the Descemet's membrane and a bit of the stroma, replacing it with a
healthy donor endothelium and equivalent bit of stroma. This is a
procedure that requires a lot of skill and practice. The upside is
that the epithelium is almost undisturbed, there are few or no
stitches (hence no astigmatism), and healing is faster. The new
endothelium is able to begin its pumping work and return the eye
to transparency.
There are several detailed explanations of the various newer
procedures available to our Fuchs' Friends. My statements above
are meant to be merely an overview to distinguish the "full
thickness transplant" from the "partial thickness transplant."
Research is ongoing. Some day in the future the eye specialists
may be able to inject some new endothelial cells into our eyes and
get them to reproduce at the proper slow rate. But as of now,
2005, our best cure is some type of corneal transplant.
Before I conclude, I must mention Dr. Castroviejo, who was the
first doctor in the United States to do successful corneal
transplants starting in the 1940's. One of his patients in the
1960's was Bruce Varnum, CEO of the Georgia Eye Bank, who
describes Dr. Castroviejo as a "hero." Indeed, there are many of
us who have regained our vision through corneal transplant, and we
consider our doctors, our researchers, and our donors as "heroes."
by Dorothy Acton
Co-Founder of Fuchs' Friends
President of The Corneal Dystrophy Foundation
Copyright July 12, 2005.
Not to be published on any website nor distributed without express
written permission from a Director of The Corneal Dystrophy
Foundation, and proper credit given.
