Abstract: A monocentric bifocal contact lens with upper and lower optical power zones is connected by a transition comprising a family of sigmoidal curves. The sigmoidal curve begins with a common tangent at the boundary of the near zone and, with a reversal of sign from the near zone curve, climbs with increasing positive slope to an inflection point, whereupon it continues to climb with decreasing positive slope until reaching the distance zone curve, with which it has a common tangent. There is no discontinuity in the first derivative of the curve throughout its length. A sigmoidal curve can be constructed from numerous mathematical functions, examples of which include polynomial, conic, transendental, or cumulative distribution curves.

Abstract: A soft prism bifocal contact lenses that provides optimal vision for both distance and near objects by incorporating two or more prisms into the same lens. One or more primary prisms are used to achieve a desired vertical lens positioning on the eye and to control meridional rotation. In addition, one or more secondary prisms are used to achieve vertical lens shifting so that the desired optical power zone of the contact lens is brought before the entrance pupil of the eye at the desired time.

Abstract: A soft prism bifocal contact lenses that provides optimal vision for both distance and near objects by incorporating two or more prisms into the same lens. One or more primary prisms are used to achieve a desired vertical lens positioning on the eye and to control meridional rotation. In addition, one or more secondary prisms are used to achieve vertical lens shifting so that the desired optical power zone of the contact lens is brought before the entrance pupil of the eye at the desired time.

Abstract: Bifocal contact lenses are lenses with two zones having different optical powers, or more than two zones in which case they are also called multifocal lenses. Concentric bifocal contact lenses have two or more annular power zones with a connection that presents optical problems. These optical problems are solved in my invention by connecting the spherical power zones for far and near viewing by a unique toric transition zone. The toric transition zone provides a smooth and continuous slope that will not produce visual jump where it joins with the power zones. There is only one toric curve with the correct properties for each pair of bifocal power zone parameters, consisting of the power zone radii and widths.

Abstract: A bifocal contact lens which contains two optical powers and a structure which serves as a switch to determine which power is operative as the wearer looks alternatively at objects located at various distances. The lens switch is designed so as to be triggered by the upper lid as it covers and uncovers various portions of the contact lens when the lens wearer is looking alternatively at objects located at various distances.