To Galen, Mundinus and Tulp, Add Dua

What exactly is Dua’s layer?

It’s a thick, tough, acellular layer of collagen found just before (anterior to) Descemet’s membrane in the cornea. When you blow air through the cornea, it travels throughout the whole stroma as tiny bubbles until it reaches Dua’s layer, which is lifted up as a dome: it is impervious to air. The collagen fibers here are smaller in diameter than in the adjacent corneal stroma, meaning that there is more space between them for gel-like proteoaminoglycans. This probably explains why it does not let air through.

Did you have an inkling that this additional layer was present?

Yes. Let me give you a bit of background. Corneal transplantation had been around for over a hundred years. Initially, no matter what the problem, the whole disc was cut out and replaced. The biggest risk of this procedure was rejection, which involves the endothelium. The logical response was that when the endothelium was not involved in the disease, it should be retained, not replaced. A gentleman called Mohammed Anwar introduced the use of air to separate the inner lining of the cornea, the Descemet’s and the endothelium, from the rest. The idea was that by replacing only the rest of the cornea, you would never get graft failure due to endothelial rejection. Bingo!