Progressive-Power Lens
A progressive-power lens has one surface which satisfies the following expressions CY ( DP )= CT ( DP ) CY ( P )< CT ( P ) where CT(DP) denotes a vertical direction curvature at the distance reference point, CY(DP) denotes a horizontal direction curvature, CY(P) denotes a horizontal direction curvature at a point on the principal meridian which is located further on the near portion than the progressive start point, and CT(P) denotes a vertical direction curvature at the point.
1 . A progressive-power lens comprising:
an object-side surface; and
an eyeball-side surface,
wherein any one surface of the object-side surface and the eyeball-side surface includes
a distance portion having a distance reference point,
a near portion having a near reference point,
a progressive portion having a progressive start point provided at an end part of the distance portion side, the progressive portion being provided between the distance portion and the near portion, and
a principal meridian passing through the distance reference point, the near reference point, and the progressive start point, and
wherein the one surface satisfies the following expressions (1) to (3)
( n− 1)×( CT ( NP )− CT ( DP ))>Add (1)
CY ( DP )= CT ( DP ) (2)
CY ( P )< CT ( P ) (3)
where n denotes a refractive index of the progressive-power lens, Add denotes an addition power of the progressive-power lens, CT(DP) denotes a vertical direction curvature at the distance reference point, CT(NP) denotes a vertical direction curvature at the near reference point, CY(DP) denotes a horizontal direction curvature at the distance reference point, CY(P) denotes a horizontal direction curvature at a point on the principal meridian which is located further towards the near portion than the progressive start point, and CT(P) denotes a vertical direction curvature at the point.
2 . The progressive-power lens according to claim 1 , wherein the one surface further satisfies the following expression (4)
CY ( NP )< CT ( NP ) (4).
3 . The progressive-power lens according to claim 1 , wherein a dioptric power of the distance portion is a positive power.
4 . The progressive-power lens according to claim 1 , wherein the other surface of the object-side surface and the eyeball-side surface is a corrective surface where correction for a power set in the one surface is performed, and includes
a distance portion having a distance reference point;
a near portion having a near reference point;
a progressive portion having a progressive start point provided at an end part of the distance portion side, the progressive portion being provided between the distance portion and the near portion; and
a principal meridian passing through the distance reference point, the near reference point, and the progressive start point,
wherein the other surface satisfies the following expressions (2) and (3)
CY ( DP )= CT ( DP ) (2)
CY ( P )< CT ( P ) (3)
where, in the other surface, CT(DP) denotes a vertical direction curvature at the distance reference point, CY(DP) denotes a horizontal direction curvature at the distance reference point, CY(P) denotes a horizontal direction curvature at a point on the principal meridian which is located further towards the near portion than the progressive start point, and CT(P) denotes a vertical direction curvature at the point.