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Thread: Please help with this pt. possibly experiencing vertical imbalance....

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    Please help with this pt. possibly experiencing vertical imbalance....

    OD: -3.25 SPH
    OS: +1.75 -0.75 X 005

    ADD: 2.50
    ADD: 2.50

    Dist PD: OD:30.0 OS: 30.5

    Near PD: OD:28.5 OS:29.0


    Seg: 12.5mm (FT 28)

    Frame: A= 49.0 B=28.0 Circ: 127.2


    This patient is experiencing double vision in his near portion of his FT 28's. Would this problem be remedied with slab-off? If so, how much should be prescribed? -- Or just let me know what the slab off rx should be... This is my first time processing slab-off...
    Last edited by spex911; 07-18-2014 at 10:05 AM.

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    Master OptiBoarder mdeimler's Avatar
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    yes...just let the lab figure it out

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    The lab can calculate it just from that information above?

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    Master OptiBoarder mdeimler's Avatar
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    yes, we have software...if we don't want to do the math

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    Just order with normal script and tell the lab you want a Slab...they do the rest! Easy Peasy

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    Thanks for the help guys!! I guess the only reason I would need to know how to calculate slab-off would be for ABO advance test questions or if I worked in a lab and had to do it for a patient -- And to grasp the remedies of vertical imbalance I guess too : )

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    Master OptiBoarder OptiBoard Silver Supporter Jubilee's Avatar
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    In case you wanted to know how to do it yourself:

    1st) Calculate the power in the 90.
    OD: -3.25
    OS: +1.00 (since the axis is 5 and the amount of cyl so low, you can round it up to the full power in affect at the 90. Actual math puts it the power at 90 at -.74 instead of .75)

    2nd) Figure out the amount of prism at 8mm below OC. (8mm is the amount of down-gaze the average person has when reading.)
    OD:
    • OD: D = -3.25, d = 8 mm, P = Dd/10 = (3.25)(8)/10 = 2.6 BD
    • OS: D = +1.00, d = 8 mm, P = Dd/10 = (1.00)(8)/10 = 0.8 BU

    Total Prism difference of 3.4

    3rd) Know the difference between a Slab off and a reverse slab. Most labs will do a reverse slab because they can by the blanks from Younger, and its a lot easier than the bicentric grinding a regular slab requires. Down side is that it comes in set prism amounts. You would not be able to get exactly 3.4 diopters. It also isn't available in all materials. Bright side is that some labs are using freeform equipment to make regular slabs.


    • Slab off would be on the Most minus, least plus. So would be performed on the right lens.
    • Reverse would be.. reversed. Most plus, least minus. OS
    "Some believe in destiny, and some believe in fate. But I believe that happiness is something we create."-Something More by Sugarland

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