A theoretical model for predicting parameter changes in soft contact lenses due to bending.

Equations are presented for the theoretical determination of back vertex poser changes in soft contact lenses due to bending. The main assumption is that the volume of the lens remains unchanged. A description of changes in other lens parameters, namely, central thickness, overall diameter, and anterior radii, is presented for both spherical and toric lenses. In general, power changes predicted by the proposed model are less than those suggested by previous workers in this field. Changes however occur in other parameters which have previously been regarded as remaining constant such as the central thickness of the lens. These changes are of small degree but have significant bearing on back vertex power.