US Patent 7073906 Aspherical diffractive ophthalmic lens

A multifocal ophthalmic lens includes a lens element having anterior and posterior surfaces with a central aspherical refractive zone disposed on one of the anterior and posterior surfaces; and a diffractive bifocal zone disposed outside of the aspherical refractive zone. The central aspherical refractive zone may be disposed on the anterior surface and the diffractive bifocal zone may be disposed on the posterior surface.