I know the Opticampus site, among others, have various lens thickness calculators on them, however, I am interested in making one of my own, as a pet project, and to better understand the math. So far, I am able to calculate with a relatively small margin of error minus powered spherical lenses. However, as I frequently deal with sphero-cyls and hyperopes, the math falls apart anytime I have to give it a number that I actually DO want an answer for.

So the question is -

I'm looking for a formula to approximate the thickest (edge on a minus, and centre on a plus) portion of lens given a sphero-cylinder power. I will leave the example that broke my calculator:

Frame - A: 53 ED: 54 DBL: 16
PD - 62
Sphere +4.00
Cylinder -5.00
Axis 179
Minumum ET/CT - 1.5mm

This combo whomped my calculator for some reason, resulting in a read of only the minimum thickness, which I'm using 1.5mm for.

Any math whizzes have a formula?