Patent ID: 7021763

Claim:
Method for fabricating a double-progressive spectacle lens, comprising: selecting a suitable coordinate system K2 for the representation of a back surface; selecting a suitable grid G for the representation of a spline of the back surface of a starting lens to be optimized in the coordinate system K2; assigning sagittal height data of the back surface to a spline (back surface spline); defining a position of a center of rotation of an eye; computing principal rays from the center of rotation of the eye through the starting lens at grid points of G; computing a length of a distance between points of penetration of a thus computed principal ray through a front surface and the back surface (oblique thickness); assigning data of the oblique thickness (thickness spline) to a spline; selecting a set of assessment positions at which an optical quality is computed for a target function; suitably selecting particular optical and geometrical stipulations which are satisfied at the assessment positions; defining the target function as a deviation of the quality of an actual spectacle lens from ideal values; starting the optimization; evaluating at each one of optimization steps the optical properties in a wearing position at the assessment points using surface properties to be computed and actual principal ray data; ending the optimization when the target function is below a predetermined value, or after a specifiable maximum number of optimization steps; and fabricating a thus computed surface.