US Patent 7377637 Hybrid contact lens system and method of fitting

A hybrid contact lens comprises a substantially rigid zone having an aspheric base curve with a given apical radius and a substantially flexible hydrophilic peripheral portion coupled to the substantially rigid zone, the peripheral portion having one of a plurality of radii, wherein a conic constant of the substantially rigid zone varies with apical radius, so as to provide a nearly constant deviation between the aspheric shape of the base curve and a sphere having a radius equal to the apical radius, regardless of the length of the apical radius.