Ophthalmic lens for presbyopia and aphakia

A multifocal ophthalmic lens of homogeneous transparent optical material, useful for the correction of the refractive error and the accommodative insufficiency or absence of accommodation in presbyopia and aphakia, having a geometrically and optically continuous variable convex front surface at least a portion of which changes continuously and regularly in refractive power, and a coacting coincoid conicold surface of eccentricity zero or greater or toric back surface, said variable front surface characterized by having a single pair orthogonal principal planes each of said planes of said pairs intersecting said variable convex front surface normally at all points, the first of said principal planes, generally horizontal in use, intersecting said front surface normally in a conic great arc of eccentricity zero or greater, the derivative of curvature of said variable front surface vanishing at said great arc at least in sections by all planes orthogonal to it, said arc providing a unique tangential junction between an upper and a lower portion of said variable front surface, there being geometrical and optical continuity and a continuous and regular change in curvature and refractive power in crossing said conic great arc, without localized distortion in the field of vision through said lens, the second of said principal planes being a generally vertical plane of symmetry of said variable front surface, intersecting orthogonally said great arc and said first principal plane and forming the axis of said variable front surface, said axis intersecting the center of curvature of said great arc when its eccentricity is zero and coinciding with the major axis and intersecting both foci and the center of curvature of the apex of said great arc when its eccentricity is greater than zero, and intersecting said variable front surface normally in a principal curve in which, at the point where said axis intersects said variable front surface, namely, the axial umbilical point, the curvature of said great arc and said principal curve are equal, the derivative of curvature of said principal curve and of said great arc of said variable front surface in all meridian sections containing said axis, vanishing or zero at said axial umbilical point, said principal curve at least below said great arc, increasing in curvature and refractive power downwardly in a continuous and regular manner and at an accelerated rate with increasing distance from the axial umbilical point of said variable front surface, all transverse sections of said variable front surface below said great arc, by planes orthogonal to said principal curve, being conics of eccentricity greater than zero whose axes containing the foci of said conics lie in said vertical principal plane and intersect normally said principal curve, the curvature of said conic transverse sections at said principal curve below said great arc increasing in a continuous and regular manner at a rate substantially equal to the accelerated rate of increase in curvature of the principal curve itself, every transverse section of said variable front surface above said great arc by planes orthogonal to said principal curve being conics of eccentricity zero or greater, the lines of intersection of said orthogonal planes and said vertical principal planes all intersecting at the common center of curvature of said conics when their eccentricity is zero, the axes of said conics which contain their foci when their eccentricities are greater than zero coinciding with their respective lines of intersection of said orthogonal planes and said vertical principal plane, the eccentricities of said conic transverse section below said great arc increasing continuously and regularly with distance from said great arc, all transverse sections by planes orthogonal to the principal curve being conics of eccentricity greater than zero when said great arc is a conic of eccentricity greater than zero, the derivative of curvature of all of said conic transverse sections of eccentricities greater than zero vanishing at said principal curve, there being sufficient thickness of said lens to allow for the generating, grinding and polishing of a coacting coicoid back surface of eccentricity zero or greater or toric back surface to incorporate an ophthalmic prescription into said lens.