Centration mechanism of soft contact lenses

A theoretical model is developed in which the force that restores a soft hydrogel lens to its centered position is ascribed to flexure of the lens. It is shown that flexure makes the dominant contribution to the strain energy in the displaced position. The restoring force is calculated explicitly. The return speed is estimated explicitly, assuming that the dominant resisting force is the viscous drag offered by the postlens tear film. Satisfactory agreement with observations is found.