a contact lens of soft , pliable opthalmic plastic material , said lens when in its dehydrated state having a spherical back surface which in its hydrated state conforms to the corneal curvature of the wearer &# 39 ; s eye and , when in its dehydrated state , having an aspheric front surface which is a surface of revolution of polar coordinate form , having an asphericity which is a function of & lt ; sin & gt ; where is the polar angle , and is a radial offset of a tool - controlling circular surface .