A Controversy in Cornea

Roger F. Steinert, MD


October 01, 2013

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Hi. I'm Dr. Roger Steinert, Director of the Gavin Herbert Eye Institute and Chair of Ophthalmology at the University of California, Irvine.

I have the pleasure of talking to you this month on my Medscape blog about a very interesting set of articles and controversies that have arisen in the September issue of Ophthalmology. For those of you in the cornea world, you will realize that I'm talking about the publication of the purported discovery of a new layer in the cornea, the self-named Dua's layer by one of the co-authors, Dr. Harminder Dua.[1] This received quite a bit of publicity when the e-print in advance of publication was widely disseminated in the popular press. There was much excitement about the unexplained and surprising discovery of a previously unrecognized part of the human body.

Dr. Dua and his coauthors looked at the behavior of the separation of Descemet's membrane from the posterior stroma using the big bubble technique in a laboratory study. They found that in many cases, there was an adhesion of a layer of posterior stroma ranging from 5 to 13 microns thick. They felt that this was an acellular layer and therefore similar in fashion to Bowman's layer in the front, which we all know is acellular. You should read this article very carefully. It has some interesting lessons about the big bubble separation and some of the challenges therein.

You should also carefully read the article that precedes it, from Schlötzer-Schrehardt and colleagues.[2] Their group has done a lot of very solid work in corneal structure and anatomy. In this study, they looked at hundreds of specimens prepared for deep membrane endothelial keratoplasty (DMEK) with peeling techniques and tried to discover why there was occasionally an inability to peel off Descemet's membrane, and what the difference was in those corneas. In a nutshell, they found some interlocking peg-like adhesions that would inhibit a reasonable separation of Descemet's membrane, as well as a suggestion that some adhesive glycoproteins are present in some patients that cause a greater-than-normal amount of adhesions in Descemet's membrane.

The controversy over the so-called Dua layer led to an editorial with the first author, James Jester,[3] the esteemed corneal anatomist, physiologist, and specialist in imaging. He put together a team of very well-known corneal anatomists and physiologists, as well as a couple of clinicians, including Mark Mannis and myself. We tried to be as objective as possible in this editorial, pointing out what was known and what was not known, as well as some of the issues of corneal structure. It does include a transmission electron micrograph showing a keratocyte within 5 microns of Descemet's membrane, so it is not an acellular area of the cornea by any means. Basically, we came to the conclusion that variability in the separation of Descemet's membrane with the big bubble or any other technique does help to show that there are differences in the adhesion of the Descemet's membrane and the behavior of the stroma that are in part structural. We have been continuing to learn more and more about those structural differences, starting with the appreciation of the origin of ectasia, where the anterior half of the cornea has bridging fibers running front to back, and the posterior cornea has much more parallel belts in the sidewall or tread of a tire.

You might also turn your attention to the editorial by Ivan Schwab,[4] a very erudite discussion of the issue of nomenclature in medicine and the naming of layers, tissues, and organs. We all know that today it is quite frowned upon to use names of scientists to describe tissues. It's much more appropriate and helpful to use anatomic terms or physical terms that make sense. We've been trying to slowly move away from the tendency to use colloquial terms and names.

Again, I would like to direct your attention to the September issue of Ophthalmology. Read both of those scientific articles and then read the 2 editorials. I think you will find them interesting and instructive. It is one more step towards trying to understand and control some of the forces that are at play when we perform procedures like DMEK, as well as the ongoing attempt to find more reliable ways to transplant the portion of the cornea that is diseased, not do more surgery than is necessary, and hopefully get better visual acuity.

This is Dr. Roger Steinert on behalf of Medscape. Thank you very much for listening, and feel free to send in your comments. So long for now.


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