Patent ID: 8376546

Claim:
A method of designing a progressive-addition lens, in which a distance dioptric power and an addition dioptric power measured by a lens power measuring apparatus substantially agree with respective prescribed powers, wherein the lens has a progressive surface and an aspherically designed surface formed of an aspherical or atoroidal surface on the back surface of the lens, the method comprising: calculating an addition dioptric power, a distance dioptric power and a prism dioptric power on the aspherically designed surface under the assumption that a measurement is made by using the lens power measuring apparatus, and calculating respective amounts of deviance of the calculated addition dioptric power, distance dioptric power and prism dioptric power from an addition dioptric power, a distance dioptric power and a prism dioptric power calculated when the back surface of the lens is formed of a spherical or a toroidal surface; moving the back surface of the lens such that a center of the aspherical or atoroidal surface is moved downward a predetermined distance in a vertical direction while the prism dioptric power at a point, wherein the prism dioptric power is measured, is kept constant when the amount of the deviance of the addition dioptric power exceeds a predetermined threshold; deforming the back surface of the lens, thereby eliminating the deviated amount of the distance dioptric power when the amount of the deviance of the distance dioptric power exceeds a predetermined threshold; and changing a direction of the back surface of the lens such that a normal line direction at a position corresponding to a prism reference point of the back surface of the lens is changed, thereby eliminating a difference ΔDp of the prism dioptric power when the difference ΔDp of the prism dioptric power exceeds a predetermined threshold.