To help determine edge and center thickness

  Sphere Cylinder Axis
Front Curve:
Back Curve:
Thickness (Edge T. or Center T.):
Meridian: (Assumed 180 if blank)

Instructions: Fill in the form as best as you can. (The ED so far doesn't do anything yet) The meridian deals with the angle at which you want to figure out the thickness. For the most part, this value will be 180. But let's say you want to know how thick a lens will be on the top, that meridian will be 90. Lets say you have a pair of Aviator style glasses and want to know how thick it's going to be at a 40 degree angle (you can guesstimate or you can get out a protractor and measure the angle at which you want the measurement in. All this does is adjust the power of the lens so that you get the correct power in that meridian and give you a more accurate answer. Most people want to know how thick the lens will be on the side so the 180th meridian is assumed.

If you put in front and back curves, I also calculate the back vertex power so that you can simply hit back, insert the back vertex power into the Rx, and compare the result with the approximate formula.

Note: This really only works for spherical lenses. Aspheric and/or atoric lenses should theoretically be thinner still.

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