For manufacturing ophthalmic lenses and other optical form bodies made of plastic material, plastic form parts are used which are made by non-cutting shaping and are then further worked by mechanical production steps. Said plastic form parts are circular blanks (1) made of two different plastic materials which are firmly joined to each other. Thereby, an interior lens element (2) that consists of a high-quality material is concentrically surrounded by a ring fixture (3) which consists of a low priced material. Either surface of the lens element (2) may feature any given geometry. During mechanical working, the ring fixture (3) is used for mounting as well as for depositing and, in addition, for stabilizing the workpiece (9). For this reason it is partially maintained throughout the mechanical working and is cut off at the end only.