Induced prism calculation

[GJU656]

Can someone check my calculations here for the amount of induced prism when the center of both lenses is off by 2mm? Here is my example:

-3.75 -1.25 ---> -4.25 *.2 = .85
-4.00 -0.75 ---> -4.38 *.2 = .88

Total induced prism is 1.73.

If I'm not mistaken, the ANSI tolerance is something like .75, right?

[HarryChiling]

The standard dictates 2/3 D prism horizontally.

For the power you shouldn't use the spherical equivalent. You need to find the power on the meridian you are checking. If you want to check the power on the horizontal meridian or 180 then the equation is

Power180=Sph+Cyl*sin(axis)^2

and for the horizontal meridian,

Power090=Sph+Cyl+cos(axis)^2

this will give you the power that you would then plug into prentices rule to find the prism

Prism=Power*Decentration(cm)

[Steve Machol]

Why you you list your occupation as: Consumer or Non-Eyecare field