Patent ID: 6953248
Filing Date: 2005-10-11
Classification: G02C

Abstract:
1. A progressive power lens belonging to a series of progressive power lenses which is designed such that lenses belonging to said series of progressive power lenses have substantially the same basic specification and said lenses belonging to said series of progressive power lenses have different base curves, said progressive power lens having a front surface and a rear surface, at least one of said front and rear surfaces including: a distance portion having refractive power for distance vision; a near portion having refractive power for near vision; and a middle portion in which refractive power continuously changes to connect the refractive power of the distance portion and the refractive power of the near portion, wherein if a first lens- and a second lens randomly chosen from said series of progressive power lenses have a common spherical refractive power Sph [diopter] at distance reference points thereof, the Sph is greater than or equal to +1, and a base curve BC where Wdt represents a width of an area in which transmission astigmatism is less than or equal to one-half of additional dioptric power AD [diopter] which is defined as a difference of the refractive power at a distance reference point and the refractive power at a near reference point, Wdt being measured in a horizontal direction at a point in the distance portion shifted upward in a vertical direction by a certain distance from a geometrical origin of said progressive power lens, Wnt represents a width of an area in which transmission astigmatism is less than or equal to one-half of the AD, Wnt being measured in the horizontal direction at a point in the near portion shifted downward in the vertical direction by a certain distance from the geometrical origin, Wds represents a width of an area in which surface astigmatism is less than or equal to one-half of the AD, Wds being measured in the horizontal direction at a point in the distance portion shifted upward in the vertical direction by a certain distance from the geometrical origin, Wns represents a width of an area in which surface astigmatism is less than or equal to one-half of the AD, Wns being measured in the horizontal direction at a point in the near portion shifted downward in the vertical direction by a certain distance from the geometrical origin.