Abstract

The obvious purpose of an ophthalmic multifocal is to enable the wearer to see clearly at a multiplicity of viewing distances. Bifocals and trifocals accomplish the task admirably, but introduce discontinuities of power and prism into the visual field. Progressive-addition lenses offer distinct optical advantages over conventional multifocals: they provide clear vision at all viewing distances as well as continuity of the visual field. But for maximum visual comfort, the inherent aberrations of the progressive surfaces of these lenses must be minimized and the flow of surface power must be smooth. The present paper addresses the mathematical problem of smoothness and shows how the degree smoothness of the progressive surface can be optimized using the Dirichlet principle.¹

© 1991 Optical Society of America