Patent ID: 7874673

Claim:
A progressive power lens, comprising: a pair of an outer refractive surface and an inner refractive surface, at least one of the outer refractive surface and the inner refractive surface being a progressive surface, relationships as follows being defined with respect to a lens to be actually worn: SV=SPH+CYL ·{ cos( AX )} 2 (1); Dm 1=( N− 1)· Cm 1 (2); and Dm 2=(1 −N )· Cm 2 (3), where: SPH represents a spherical power; CYL represents a cylindrical power; AX represents a cylinder axis; ADD represents an addition power; N represents a refractive index of the lens; SV represents a vertical refractive power; Cm 1 represents a curvature of a cross-section of an outer surface taken along a main fixation line; Cm 2 represents a curvature of a cross-section of an inner surface taken along the main fixation line; Dm 1 represents a surface power of the cross-section of the outer surface taken long the main fixation line; Dm 2 represents a surface power of the cross-section of the inner surface taken along the main fixation line; PA represents a pantoscopic angle, the angle being defined as positive when formed in a direction in which the lens is laid down; Y represents a vertical distance from a prism reference point, the distance being defined as positive when taken in an upper direction of the lens fitted in a frame; Yf represents a Y-coordinate of a point located on the main fixation line and within an upper range of the vertical distance Y of 5<Y<15; and Yn represents a Y-coordinate of a point located on the main fixation line and within a lower range of the vertical distance Y of −15<Y<−5, relationships as follows being defined with respect to a lens designed for a standard pantoscopic angle: Dm 1 o =( N− 1)· Cm 1 o (2A); and Dm 2 o =(1 −N )· Cm 2 o (3A), where: Cm 1 o represents a curvature of a cross-section of an outer surface taken along the main fixation line; Cm 2 o represents a curvature of a cross-section of an inner surface taken along the main fixation line; Dm 1 o represents a surface power of the cross-section of the outer surface taken along the main fixation line; Dm 2 o represents a surface power of the cross-section of the inner surface taken along the main fixation line; and PAo represents a pantoscopic angle defined as positive when formed in a direction in which the lens is laid down, relationships as follows being defined: Δ PA=PA−PAo (4); and Δ Dm ( Y )={ Dm 1( Y )+ Dm 2( Y )}−{ Dm 1 o ( Y )+ Dm 2 o ( Y )} (5), where: ΔPA represents a deviation of the pantoscopic angle between the pantoscopic angle of the lens to be actually worn and the standard pantoscopic angle; and ΔDm(Y) represents a difference between a sum of the surface powers of the cross-sections of the outer surface and the inner surface of the lens to be actually worn taken along the main fixation line and a sum of the surface powers of the cross-sections of the outer surface and the inner surface of the standard lens taken along the main fixation line, and relationships as follows being satisfied: ΔPA≠0 and ΔDm(Yf)≠ΔDm(Yn) (6).