Optimizing Design Of Progressive Addition Lenses

Since the progressive addition lens (PAL) has some advantages over bifocal and trifocal lens in correcting myopia and presbyopia in particular, it is more accepted by consumers. The PAL provides a continuous range of accommodative powers, and avoids having a visible dividing line or image jump like bifocal lens. The PAL has become a popular approach to the management of myopia and presbyopia in resent years. In the design process, the initial designed PAL often has some shortcomings, such as the clear region on distance-vision is not broader, the intermediate zone is narrower and the astigmatism is larger. Two optimizing design methods are proposed to optimize the preliminary designed surface shape data of the PAL.1. Optimizing the PAL by solving the partial differential equationThe power plot is obtained base on the inversion of the preliminary designed surface shape data. The power plot is changed by adjusting the optimizing factor of an optimization function. Otherwise, the optimized plot of the mean power can also be derived by shifting the mean power of one selected region to another and then by interpolating and smoothing. A partial differential equation of the elliptic type is founded based on the changed mean power. The optimized vector heights of the surface are solved out. Compared with the original lens, the clear region on the intermediate zone become wider by the optimization factor method and the clear region on distance-vision is broaden by the shifting power method.2. Optimizing the PAL by mean curvature flowAn optimizing design concept is presented that the more the surface of the progressive lens becomes closer to spherical by the process of mean curvature flow, the more the astigmatism is smaller. The principle of mean curvature flow operator and the optimizing algorithm are illustrated. An initial designed progressive lens and an optimized lens by this method are manufactured and tested. Compared with the original lens, the optimized lens has smaller maximum astigmatism and larger clear region on the distance-vision zone.All the optimizing methods presented in this paper can reduce the undesirable astigmatism in some regions of the progressive lens surface while retaining desirable optical features of the progressive lens. And the optimizing approaches can optimize the progressive lens given by any design method.