Contact lens flexure and the associated change in residual astigmatism were measured with lenses of various center thicknesses on corneas of various toricities. On spherical and near-spherical corneas, none of the lenses flexed significantly or altered the residual astigmatism. On toric corneas, thick lenses (t > 0.13 mm) did not flex significantly: however, thin lenses (t < 0.13 mm) did flex significantly, and did alter residual astigmatism in a predictable manner. The findings of this study can be used to alter the amount of residual astigmatism of toric corneas by making appropriate changes in contact lens center thickness.