Progressive power ophthalmic lenses

Claim 1

In a progressive power ophthalmic lens having two refractive surfaces one of which is divided into three viewing zones comprising an upper distance portion, an intermediate progressive portion and a lower near portion, and having a principal vertical meridian defined by a sequence of points traversing said zones, wherein said distance portion occupies approximately the upper half of said lens and is of substantially spherical configuration providing a substantially constant focal length for distant vision, wherein said near portion occupies a lower portion of said lens and is of substantially spherical configuration providing a substantially constant focal length for near vision, and wherein said intermediate progressive portion lies between and has defined boundaries with said distance and near portions and has a varying curvature which increases continuously and progressively along said meridian from a minimum value, which approximates the curvature of said distance portion, to a maximum value, which approximates the curvature of said near portion, the improvement wherein said intermediate progressive portion is defined by a series of generating curves passing successively through all points of the meridian within said progressive portion, said generating curves being the lines of intersection of an ordered sequence of spheres and a corresponding ordered sequence of cylinders, said spheres being tangent to points on the meridian and having radii equal to the radius of curvature of the meridian at each point, and said cylinders having generating lines parallel to a line normal to the center point of said lens, the generating curves being so constructed and arranged that aberrations are distributed uniformly around said near portion with at least approximate preservation of orthoscopy.