Ophthalmology textbooks describe five layers of the human cornea. They’ll have to be rewritten, says University of Nottingham Professor Harminder Dua, who recently discovered a sixth layer.

“Having identified this new and distinct layer deep in the tissue of the cornea, we can now exploit its presence to make operations much safer and simpler for patients,” she said in a press release.

“From a clinical perspective, there are many diseases that affect the back of the cornea which clinicians across the world are already beginning to relate to the presence, absence or tear in this layer.”

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The new layer, called the Dua’s Layer in honor of the professor, is described in the journal Ophthalmology. It’s too thin to be seen; at 15 microns, it’s smaller than beach sand and mist, and makes up a small fraction of the cornea, which is 550 microns thick. It’s located toward the back of the cornea. The scientists detected it through electron microscopy after injecting tiny bubbles of air into donated corneas to separate the layers.

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Already, scientists say they have a better understanding of certain diseases of the cornea. Corneal hydrops, for example, occurs when fluid builds up in patients with a deformity of the cornea and produces a bulge. Now researchers think the bulging is caused by a tear in the Dua’s layer.

It could also help in eye surgeries: A surgeon could inject a bubble next to the Dua’s layer to test how strong it is, for example.