Large diameter positive power ophthalmic lens

摘要

A positive power ophthalmic lens has a central optically active area the diameter of which is at most equal to the diameter of its geometrical contour. It has an optional peripheral merging area around the central optically active area, between the latter and the geometrical contour. The diameter D1 in millimeters of the central optically active area is related to the power P of the lens in diopters by a general equation of the type: D1=a-b.p where a is a numerical parameter taking a value between 84 and 89 and b is a numerical parameter taking a value between 4 and 4.9. This equation makes it possible to obtain well corrected positive power ophthalmic lenses with a large diameter that are relatively light in weight.