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Abstract

A method for forming a thermoplastic preform into a lens by compression molding between a pair of molds is provided. In another aspect of the invention a set of novel preforms made from a thermoplastic material is provided. The preforms have different radii of curvature. Preferably each different curvature preform comes in different weights desirably two or three different weights. A series of mating concave and convex mold halves are provided for use with the preforms. According to the invention a limited number of concave mold halves are provided. A wide range of single vision and multifocal lenses can be supplied from three (3) to six (6) base curve concave molds halves having different radii of curvatures. According to the invention a first concave mold half with a radius of curvature of less than two (2) diopters is provided. Each successive concave mold half has a radius of curvature of from one (1) to three (3) diopters greater than the previous mold half in the series. Thermoplastic preforms are associated with the different concave mold halves. Each preform has a convex side for placement in a concave mold half and a flat side or substantial flat side or a concave side curve for engagement with a convex mold half. The convex side of the preform has a radius of curvature in diopters of 1 to 5 diopters greater than the radius of curvature of the concave mold half. Desirably the radius of curvature of the preform is 2 to 4 diopters greater than the radius of curvature of the concave mold desirably about 3 diopters or above and preferably 3 diopters greater than that of the concave mold. A convex mold half is provided, for mating with the concave mold to complete the finished lens having a desired magnification strength.

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First Claim