Short channel progressive addition lenses

1. A method for designing a progressive addition lens, comprising the steps of:

a.) providing a first design for a progressive addition surface which includes a nominal surface power and a nominal cylindrical power that at least in part determine a channel length;

b.) calculating a scaled surface power and scaled cylinder power for each of a plurality of base curves based on the nominal surface power and the nominal cylindrical power, so that the channel length is decreased or increased;

c.) using the scaled surface and cylinder powers to generate a set of power and cylinder targets; and

d.) optimizing the first design using the power and cylinder targets to produce a second optimized design,

wherein the scaled surface power or cylinder powers are determined in step b) according to the following equations:

P ( x,y )= p ( x′,y′ )

C ( x,y )= c ( x′,y′ )

Wherein P(x,y) is a scaled surface power;

p(x′,y′) is a nominal surface power;

C(x,y) is a scaled cylinder power;

c(x′,y′) is a nominal cylinder power x′=x/x_scale; and

y′=(y-shift)/y_scale+shift.

2. The method of claim 1 , wherein x_scale is 0.7 to 1.3 and the shift is −6 mm to 0 mm.

3. The method of claim 1 , wherein x_scale is 1 and the shift is −3 mm.

4. The method of claim 1 , wherein step d.) further comprises optimizing by determining a surface that minimizes the function:

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Φ

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w_c

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wherein x and y are points sampled over the surface of the lens;

w_p(x,y) is a power weight;

P(x,y) is a scaled surface power;

Φ(x,y) is a surface power calculated at each point (x,y);

w_c(x,y) is a cylinder weight;

C(x,y) is a scaled cylinder power; and

cyl(x,y) is the surface cylinder calculated as each point (x,y).

5. The method of claim 1 , further comprising determining the surface powers and cylinder powers using ray tracing for the lens in an as-worn position.

6. The method of claim 4 , further comprising determining the surface powers and cylinder powers using ray tracing for the lens in an as-worn position.

7. The method of claim 1 , wherein the second design comprises a peak, unwanted astigmatism equal to 0.8*add power.

8. The method of claim 1 , wherein the second design comprises a reading width >5.7 mm.

9. The method of claim 1 , wherein the second design comprises a reading area defined by a peak power within 2 mm of a near reference point.

10. The method of claim 1 , wherein the second design comprises a base power+add power+0.05 diopters<peak power<a base power+an add power+0.15 diopters.

11. The method of claim 1 , wherein the second design comprises one or more lines of a constant power near a reading zone, the one or more lines are nominally elliptical in shape having a power decreasing in all directions from a peak defined by a peak power within 2 mm of a near reference point and a base power+add power+0.05 diopters<peak power<a base power+an add power+0.15 diopters.

12. The method of claim 1 , wherein the second design comprises a surface area having unwanted astigmatism above (0.9*add power)*0.6 that is <500 mm 2 .

13. The method of claim 1 , wherein the second design comprises a distance width >40 mm, wherein the distance width is defined by a cylinder power of 0.5 diopters.

14. The method of claim 1 , wherein the second design comprises a distance width of >150-167*(addpower)+69*(add power) 2 −9.7*(add power) 3 for sphere powers of 0 diopters or>175-199*(addpower)+96*(add power) 2 −12.5*(add power) 3 for sphere powers 2.5 diopters or >150-174*(addpower)+75.8*(add power) 2 −11.1*(add power) 3 for sphere powers −2.5 diopters, where the distance width has units of mm for add powers expressed in units of dioptres.

15. The method of claim 1 , wherein the second design comprises a near reference point at 15 mm below a fitting point.

16. The method of claim 1 , wherein the second design comprises a channel length 12 mm in length.

17. The method of claim 1 , wherein the second optimized design comprises one or more of:

a.) a peak, unwanted astigmatism, equal to 0.8*add power;

b.) a reading width >5.7 mm;

c.) a reading area defined by a peak power within 2 mm of a near reference point;

d.) a base power+add power+0.05 diopters<peak power<based power+add power+0.15 diopters;

e.) one or more lines of a constant power near a reading zone, wherein the one or more lines are nominally elliptical in shape having a power decreasing in all directions from a peak defined by characteristics c.) and d.);

f.) a surface area having an unwanted astigmatism above (0.9*add power)*0.6 that is <500 mm 2 ;

g.) a distance width >40 mm, wherein the distance width is defined by a cylinder power of 0.5 diopters;

h.) a distance width of >150-167*(addpower)+69*(add power) 2 −9.7*(add power) 3 for sphere powers of 0 diopters or >175-199*(addpower)+96*(add power) 2 −12.5*(add power) 3 for sphere powers 2.5 diopters of >150-174*(addpower)+75.8*(add power) 2 −11.1*(add power) 3 for sphere powers −2.5 diopters, where the distance width has units of mm for add powers expressed in units of dioptres;

i.) a near reference point at 15 mm below a fitting point; and

j.) a channel length 12 mm in length.