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Thread: Prism thinning in combination with prescribed prism

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    Master OptiBoarder OptiBoard Silver Supporter ak47's Avatar
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    Prism thinning in combination with prescribed prism

    When there is prescribed prism, does that necessarily mean that prism thinning should not be used? What if the prescribed prism is only horizontal?

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    Ghost in the OptiMachine Quince's Avatar
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    I guess I have never thought too far into it, but I always use Prism thinning when recommended by Visual Lab regardless of whether or not there is prescribed prism. I only ever change the setting when I'm running a single lens and the program doesn't suggest using it.
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    I think it depends on the diagnosis, ak. Most of the time it should wash out, the prism thinning on each lens will offset each other and the net prism differential (even if vertical) should still add up on the prism line. I suppose it's possible an Rx needs that prism correction mapped "just so" against the MRP, but I doubt that patient ends up getting to be a PAL wearer.

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    Master OptiBoarder MakeOptics's Avatar
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    Quote Originally Posted by ak47 View Post
    When there is prescribed prism, does that necessarily mean that prism thinning should not be used? What if the prescribed prism is only horizontal?
    You can use prism thinning with prescribed prism. The only time any prism is problematic is if the user views through a high amount of prism and the material is crummy = chromatic aberration which causes loss in visual acuity. In PALs and MFs remember to compute the off axis prism and the CA at that point to determine is loss of visual acuity would be problematic, this applies to non prism lenses as well since any off axis viewing would introduce prism at the point in the lens the rays pass through. I just got an idea fro a visual ISO-Prism generator to show the potential problem spots. (ideas are free, enjoy)
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