Patent ID: 8523633

Claim:
A process for the manufacture of a semi-finished product from a blank, the semi-finished product for a plus ophthalmic lens with a toric or atoric concave rear side that is designed as a prescriptive surface, comprising the steps of: a) blocking a blank on the front side for the purpose of machining the rear side for generating the prescriptive surface, and wherein the blank has a diameter D R and a front side that has a curvature radius r V ; and b) manufacturing the prescriptive surface only across a part of a diameter D where D<D R , whereby in the regions of the rear side in which a thickness h B of a rim would become smaller than a minimum dimension h min due to generation of a base radius r B , a deviation from the curvature of the prescriptive surface is applied that leaves an allowance thus creating a secondary rim area so that the thickness of the resulting manufactured semi-finished product formed from the blank is not less than the minimum dimension h min at any point, and wherein the thickness h B of the rim is, at a maximum, five times as large as a thinnest point S of the semi-finished product; and c) unblocking the semi-finished product, following optional further processing.