Multifocal diffractive lenses are used widely in ophthalmology. This paper provides a general mathematical formula to summarize various multifocal diffractive lens designs and introduces a novel, design: the subzonal multifocal diffractive (SMUD) lens. Analytical and numerical methods of SMUD lens design are elaborated in detail. A number of trifocal and quadrifocal SMUD lens designs of high diffraction efficiency are presented. Fresnel zone spacing factors are introduced to take into account the incidence of a converging or diverging beam and the curvature of the substrate on which the diffractive surface is created. Apodization and ophthalmic astigmatism correction related to diffractive lenses are also discussed.