| 摘要 |
A monocentric seamless bifocal lens is manufactured by obtaining a lens blank having concentric top and bottom spherical surfaces, and grinding the bottom surface to form a major segment having one spherical radius and a minor segment having a second spherical radius. The lens is then placed on a block having two spherical surface portions whose shape conforms to the shape of the major segment, but differs from the shape of the minor segment. The block also has a slight dihedral angle, so that a space remains between the block and at least part of the minor segment. As it rests on the block, the lens is heated so that it sags under its own weight until its bottom surface assumes the shape of the block, and the radius of curvature of the upper surface becomes non-uniform. Finally the bottom surface of the lens is ground and polished to a uniform spherical radius.
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