Importance

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Abstract

Disclosed is a high index of refraction glass base lens in combination with readily castable CR-39 or equivalent plastic veneer overlay. The high index of refraction glass serves to bend light quickly and radically to eliminate the need for excessive lens thickness and curvature, thus reducing the overall mass and weight of the lens. For example: A -10.00 D. prescription lens made from CR-39 plastic requires front and back curvatures totalling -10.60 D. with an accompanying edge thickness at 71 mm diameter of 17.3 mm. This same -10.00 D. prescription lens made from the standard crown glass of the ophthalmic industry (index of refraction 1.523) would require a total front and back curves of -10.00 D. and will have an accompanying edge thickness at 71 mm diameter of 16.5 mm. The subject invention lens utilizes high index of refraction glass, so that a -10.00 D prescription can be made from a lens embodiment whose front and back curves total -6.57 D. with an accompanying edge thickness at 71 mm of 9.1 mm. The veneer overlay has a central zone with no correction, and negative correction on its periphery. Thus asphericity is provided irrespective of whether the base lens correction is positive or negative. In addition, bifocal, trifocal, or other vocational corrections may be positioned in the veneer overlay.

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First Claim