The cornea swells in the posterior direction under hydrogel contact lenses.

Two mathematical models were developed to describe the topographical corneal swelling response to hydrogel contact lenses and the effect of these changes on refractive error. In one, corneal thickness changes resulted in deformation of the anterior corneal surface. In the other, the posterior surface only was deformed. Refractive error, corneal thickness and corneal shape were monitored in a sample of adapted contact lens wearers with one eye patched for 4 h while wearing a soft contact lens. The experimental data were most consistent with the model in which the posterior surface only was deformed.