Patent ID: 6851806

Claim:
A progressive multifocal lens for correcting an eyesight, said lens having a progressive refractive surface on an eyeball side, said progressive refractive surface comprising: a far-use portion, a near-use portion having a refractive power different from the far-use portion, and a progressive portion whose refractive power changes progressively between the far-use and near-use portions, wherein the progressive refractive surface is a combination of an original progressive refractive surface for remedying only eyesight and an original toric surface for remedying only astigmia based on a following formula: z p = 2 ⁢ ( ( c p + c y ) ⁢ y p 2 1 + 1 - ( c p + c y ) 2 ⁢ y p 2 ) - ( c p + c x ) ⁢ ( ( c p + c y ) ⁢ y p 2 1 + 1 - ( c p + c y ) 2 ⁢ y p 2 ) 2 + ( c p + c x ) ⁢ x p 2 1 + ( 1 - ( c p + c x ) ⁢ ( c p + c y ) ⁢ y p 2 1 + 1 - ( c p + c y ) 2 ⁢ y p 2 ) 2 - ( c p + c x ) 2 ⁢ x p 2 where z-axis is an axis which passes through a center of the progressive refractive surface from an object side onto the eyeball side, x-axis is in a direction of an cylinder axis of the original toric surface, and y-axis is an axis which is orthogonal to the z-axis and the x-axis, z p is any point P(x p , y p , z p ) of the combined refractive surface, C p is an approximate curvature of the original progressive refractive surface, C x is a curvature in the direction of the cylinder axis of said original toric surface, and C y is a curvature in a direction orthogonal to said cylinder axis.