Corneal Anatomy 101

A Simple Analogy

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:

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.


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