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Thread: Help with exam prep question.

  1. #1
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    Help with exam prep question.

    Can someone please explain (with some detail if possible) why (C) is the correct answer. Thanks.

    Correct the imbalance in the following prescription by use of “slab off” (10mm reading depth) how much slab-off and in which eye?


    +5.00 -2.00 x90
    +3.37 -3.00 x90


    (A) 1.20 BU in OD
    (B) 1.20 BU in OS
    (C) 1.60 BU in OS
    (D) 1.60 BU in OD

  2. #2
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    The first step is to determine the power in the 90th meridian in each eye. That's given: +5.00 in the right eye; +3.37 in the left.

    Next, use Prentice's rule. Power x mm decentered divided by ten.

    OD +5.00 x 10/10 = 5.00 prism diopters BU
    OS +3.37 x 10/10 = 3.37 prism diopters BU

    There is an imbalance of 1.63 diopters BU in the right eye.

    Slab off calls for BU prism in the eye with the most minus (or least plus) which is the left eye.

    Therefore the the closest choice is (C) 1.6 BU in OS

    That will balance the excess prism in the OD

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    Thank you so much Gary.

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    I am also having a hard time with the power at meridians! I cant understand the oblique power formula anyone got a detailed answer??

  5. #5
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    Quote Originally Posted by sp909 View Post
    I am also having a hard time with the power at meridians! I cant understand the oblique power formula anyone got a detailed answer??
    Welcome to Optiboard.

    I hope this helps:

    http://www.nfos.org/degree/opt11/module_10a.html

  6. #6
    ABOM Wes's Avatar
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    For the purpose of attempting the National Opticianry Competency Examination (NOCE, which most of you like to call the ABO), you need to know the following:

    @ axis, 0% cylinder is in effect
    30° from axis, 25% cylinder is in effect
    45° from axis, 50% cylinder is in effect
    60° from axis, 75% cylinder is in effect
    90° from axis, 100% cylinder is in effect

    To understand the real formula, and all of the rest you'll need as an optician, buy Optical Formulas Tutorial
    Wesley S. Scott, MBA, MIS, ABOM, NCLE-AC, LDO - SC & GA

    “As our circle of knowledge expands, so does the circumference of darkness surrounding it.” -Albert Einstein

  7. #7
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    There may be something here that could help, I didn't dig around. This is a site of a fellow Optiboarder.

    http://www.opticaled.com/articles/

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    ABOM Wes's Avatar
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    Thanks, Fezz. I typed that for nothing.

    *clarification: don't you just hate it when you go to post and someone else beats you to it, and gives a better answer to boot?*
    Last edited by Wes; 11-16-2011 at 08:49 PM.
    Wesley S. Scott, MBA, MIS, ABOM, NCLE-AC, LDO - SC & GA

    “As our circle of knowledge expands, so does the circumference of darkness surrounding it.” -Albert Einstein

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    Sorry about that!

  10. #10
    ABOM Wes's Avatar
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    Np.
    Wesley S. Scott, MBA, MIS, ABOM, NCLE-AC, LDO - SC & GA

    “As our circle of knowledge expands, so does the circumference of darkness surrounding it.” -Albert Einstein

  11. #11
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    Quote Originally Posted by Wes View Post
    To understand the real formula, and all of the rest you'll need as an optician, buy Optical Formulas Tutorial

    +1!

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