title: On the relation between power and astigmatism near an umbilic line.
abstract: The relation between the variation of power and astigmatism in a progressive power optical element is considered. The classical Minkwitz identity is revisited. Then, it is shown how to extend this identity, which applies to the geometry of surfaces, to optical parameters that are determined by the geometry of reflected or refracted wavefronts.
authors.affiliation: Department of Mathematics, Technion, Haifa 32000, Israel. koby@math.technion.ac.il
authors.forename: Jacob
authors.initials: J
authors.lastname: Rubinstein
mesh_terms: D005139:Eyeglasses; D008962:Models, Theoretical; D055620:Optical Phenomena; D013499:Surface Properties