Corneal swelling caused by contact lens wear was investigated by measuring corneal thickness changes of several subjects wearing well- and poorly-fitted lenses. All subjects showed initial thickening. However, with continued wear, some corneas returned to normal thickness while others did not. At least two factors are believed to be responsible for the observed changes in corneal thickness. Increased lacrimation occurring during the adaptation period of contact lens wear may reduce tear film osmolarity, thereby causing 2% to 4% increase in thickness. A tightly-fitted contact lens appears to deprive the cornea of oxygen. Below some critical oxygen tension level under the lens, corneal swelling occurs. With a very tight lens, the swelling curve closely approximated that of a cornea in an oxygen-free environment.
Mandell RB, Polse KA, Fatt I. Corneal Swelling Caused by Contact Lens Wear. Arch Ophthalmol. 1970;83(1):3-9. doi:10.1001/archopht.1970.00990030005003