Patent ID: 8100529

Claim:
A progressive-addition lens, comprising: a progressive surface only on a front surface of the lens; on a back surface of the lens, an aspherically designed surface formed of an aspherical or atoroidal surface; and a portion with power for distance vision and a portion with power for near vision wherein dioptric power is continuously changed from one portion to the other portion wherein a reference point of the aspherically designed surface, which is a point of intersection of a rotation axis of the aspherical surface and the back surface of the lens when the back surface of the lens is the aspherical surface and is a point of intersection of two principal meridians on the atoroidal surface when the back surface of the lens is the atoroidal surface, is located in a vertical direction of the lens below a prism reference point of the progressive surface, which is arranged at a center of the front surface of the lens, and above a near design reference point of the progressive surface for near vision, the reference point of the aspherically designed surface is located in the vertical direction of the lens substantially in the middle between the distance reference point for distance vision and the near design reference point on the progressive surface, a difference of a surface power at the reference point of the aspherically designed surface with a surface power at a position on the aspherically designed surface corresponding to a distance reference point of the progressive surface is substantially equal to a difference of a surface power at the reference point of the aspherically designed surface with a surface power at a position on the aspherically designed surface corresponding to a near design reference point of the progressive surface, and a thickness of a center of the lens is set to a predetermined value.