Progressive addition lenses with reduced unwanted astigmatism
View Patent ↗The invention provides lenses in which the maximum unwanted astigmatism is reduced and distributed over a wide area.
1. A method for designing a progressive addition lens, comprising the steps of:
a.) designing a first progressive addition surface having a channel, and one or more areas of unwanted astigmatism on either side of the channel, each area of unwanted astigmatism comprising a maximum unwanted astigmatism; b.) expressing the first surface as a plurality of sag values; and c.) modifying each of the one or more areas of unwanted astigmatism to provide a second progressive addition surface in which the maximum unwanted astigmatism of each of the areas is reduced and substantially constant throughout the area;
wherein the modifying of a first area of a first unwanted astigmatism is independent of modifying all other areas of unwanted astigmatism.
2. The method of claim 1 , further comprising d.) smoothing the second surface to eliminate discontinuities.
3. The method of claim 1 , wherein step b.) further comprises expressing a surface u(x,y) as a plurality of sag values by subtracting u(x,y) from a base spherical surface u o (x, y) to yield the sag values.
4. The method of claim 1 , wherein step c.) further comprises:
(i) specifying a surface u(x,y) as a plurality of sag values at points on an x-y grid;
(ii) defining an area which area comprises a point ( X m , Y m ) of maximum unwanted astigmatism;
(iii) approximating the sag values for the area using a tone surface;
(iv) calculating principal curvatures at the point of maximum unwanted astigmatism; and
(v) adjusting the sag values until the maximum unwanted astigmatism shifts to another surface location that is within the area; and
(vi) repeating steps (iii) through (v) until the maximum unwanted astigmatism within the area is reduced and is substantially constant throughout the area.
5. The method of claim 4 , wherein the area comprises a square centered at ( X m , Y m ).
6. The method of claim 4 , wherein the area comprises a circle centered at ( X m , Y m ).
7. The method of claim 6 , wherein the circle is of a diameter of about 1 to about 10 mm.
8. The method of claim 6 , wherein the diameter of the circle is about 4 mm.
9. The method of claim 1 , wherein the lens is a spectacle lens.