| abstract |
A fast, relatively inexpensive, and simple process enables a plastic, finished, multifocal, or progressive lens to be produced from a preformed lens that has a predetermined correction (i.e., curvature or prescription) at its optical center. The method includes using a mold, an optical grade resin composition, a preformed plastic lens; contacting the preformed lens with the mold such that the surfaces of the preformed lens and the mold form a cavity enclosing the resin composition; and polymerizing the resinous composition. The cavity formed by the preformed lens and by the mold is shaped to, among other things, (1) correspond to the desired change in curvature, and (2) that the correction of the lens at the optical center of the lens obtained is substantially the same. same (preferably identical) as the correction of predetermined lenses at the optical center of the preformed lens. The preformed lens can also be cast using a non-prescription thin layer which acts as a support for the multifocal or progressive region of the finished lens. The methods described allow lenses to be cast without using conventional optical seals which are expensive. Both methods also allow for simpler repositioning of the optical center to the appropriate position relative to multifocal or progressive prescription, preferably without the use of conventional optical seals or optical center displacement elements. |