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Thread: Slab Off Question+ prism splitting

  1. #1
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    Slab Off Question+ prism splitting

    Have to make the following RX:

    Bifocal C25

    R: sph: -9,25 cyl -1,75 A: 67 Prism 5,0 B90 Add:2,0

    L: sph: -4,75 cyl -0,5 A:30 Add:2,0


    My Question now is, without the precsribed prism i need 3,95 vertical slab prism.

    The Problem is the Blank thickness it will be not thick enough, so i would split the prism as follow:

    R: 2,5 B90 + ( Slab off Prism)
    L: 2,5 B270

    or is it allowed to take the whole prescribed prism 5,0 B90 from the right lens, and put in on the left lens @ 5,0 B270.
    And make on the right lens only the slab off prism.

    Thank you
    Last edited by Rafael; 12-18-2007 at 03:15 PM.

  2. #2
    Master OptiBoarder
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    You could also use a reverse slab (left eye) and then split the prism. I might also refigure the imbalance. I'm no genius at this, but I calculate it closer to 6 diopters.

  3. #3
    OptiBoard Professional jrumbaug's Avatar
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    I wish you luck.
    In theory, you can change prism from right to left by reversing the base, but you may want to speak to the doctor first. My doctor's sister in law has an Rx with 8 diop base down in the left only. I am not allowed to split the prism. The left eye is an amblyopic eye with 20/40 va. He wants all the prism there so it will not interfere with the good vision of the right.

    Keep in mind, moving that O.C. 5 mm in the left can give you that 5 diop of vert prism. Makes you wonder if the patient was centered in front of the phoropter during the test.........

    Jim Rumbaugh

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