Progressive power lens and method of designing the same

1. 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).

2. The progressive power lens according to claim 1 , wherein the vertical refractive power SV, the deviation ΔPA of the pantoscopic angle between the pantoscopic angle of the lens to be actually worn and the standard pantoscopic angle, and a difference ΔDm(Yf) 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 at a position Yf located within the upper range of Y coordinates of the main fixation line satisfy relationships as follows:

SV<0 and ΔPA>0 and ΔDm(Yf)>0.

3. The progressive power lens according to claim 1 , wherein

the vertical refractive power SV, the deviation ΔPA of the pantoscopic angle between the pantoscopic angle of the lens to be actually worn and the standard pantoscopic angle, and a difference ΔDm(Yf) 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 at a position Yf located within the upper range of Y coordinates of the main fixation line satisfy relationships as follows:

SV>0 and ΔPA>0 and ΔDm(Yf)<0.

4. The progressive power lens according to claim 1 , wherein

the vertical refractive power SV, the deviation ΔPA of the pantoscopic angle between the pantoscopic angle of the lens to be actually worn and the standard pantoscopic angle, and a difference ΔDm(Yf) 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 at a position Yf located within the upper range of Y coordinates of the main fixation line satisfy relationships as follows:

SV<0 and ΔPA<0 and ΔDm(Yf)<0.

5. The progressive power lens according to claim 1 , wherein

the vertical refractive power SV, the deviation ΔPA of the pantoscopic angle between the pantoscopic angle of the lens to be actually worn and the standard pantoscopic angle, and a difference ΔDm(Yf) 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 at a position Yf located within the upper range of Y coordinates of the main fixation line satisfy relationships as follows:

SV>0 and ΔPA<0 and ΔDm(Yf)>0.

6. The progressive power lens according to claim 1 , wherein

the vertical refractive power SV, the deviation ΔPA of the pantoscopic angle between the pantoscopic angle of the lens to be actually worn and the standard pantoscopic angle, and a difference ΔDm(Yn) 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 at a position Yn located within the lower range of Y coordinates of the main fixation line satisfy relationships as follows:

SV>0 and ΔPA>0 and ΔDm(Yn)>0.

7. The progressive power lens according to claim 1 , wherein

the vertical refractive power SV, the deviation ΔPA of the pantoscopic angle between the pantoscopic angle of the lens to be actually worn and the standard pantoscopic angle, and a difference ΔDm(Yn) 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 at a position Yn located within the lower range of Y coordinates of the main fixation line satisfy relationships as follows:

SV>0 and ΔPA<0 and ΔDm(Yn)<0.

8. The progressive power lens according to claim 1 , wherein the progressive surface is formed on an inner surface of the lens.

9. The progressive power lens according to claim 1 , wherein the progressive surface is formed on an outer surface of the lens.

10. A method of designing a progressive power lens that includes: 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, the method comprising:

designing the progressive surface to define relationships as follows 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 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 the vertical distance Y of −15<Y<−5,

designing the progressive surface to define relationships as follows 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,

designing the progressive surface to define relationships as follows:

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

designing the progressive surface to satisfy relationships as follows:

ΔPA≠0 and ΔDm(Yf)≠ΔDm(Yn)  (6).