Dellen are small, saucer-like excavations at the margin of the cornea. They occur most often following processes which produce a paralimbal elevation. It is suggested that this paralimbal elevation induces a localized break in the precorneal oily film layer of the tears which, in turn, causes a localized dehydration and thinning of the cornea. Treatment is directed towards rehydration of the cornea and reduction of the limbal elevation.
Baum JL, Mishima S, Boruchoff SA. On the Nature of Dellen. Arch Ophthalmol. 1968;79(6):657-662. doi:10.1001/archopht.1968.03850040659002