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Thread: can you place Fresnel over existing prism

  1. #1
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    can you place Fresnel over existing prism

    Hi all,

    I have an interesting problem. A patient with

    rx of:

    plano -1.00 x 175
    plano - 1.00 x 165 2.5 base up
    +2.50 add ou

    st 28

    Due to Graves disease and changes in medication this patient now requires the above rx with od 4 base down and os 4 base up. This may be temporary and I was wondering if I could place Fresnel prism over the existing prism in this patient's glasses. I have never used Fresnel ou before. I realized this would not be an ideal solution but would it work temporarily while her medications are adjusted?

    Thanks for all input!

  2. #2
    Underemployed Genius Jacqui's Avatar
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    Should work, but be ready to make new lenses just in case.

  3. #3
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    Yep, it'll work at least long enough to evaluate.

    Chip

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    Vision Equipment OptiBoard Corporate Sponsor Leo Hadley Jr's Avatar
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    Yes!!

    I did many fresnals over high prism lenses.
    Leo Hadley Jr
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    Underemployed Genius Jacqui's Avatar
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    Just don't forget that you'll only need to add 1 1/2 to the OS.

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    Master OptiBoarder OptiBoard Gold Supporter DragonLensmanWV's Avatar
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    Can you just add all of it to the OD? Just one Fresnel that way.
    DragonlensmanWV N.A.O.L.
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  7. #7
    One eye sees, the other feels. OptiBoard Silver Supporter
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    Quote Originally Posted by tolpuppy View Post
    Hi all,

    I have an interesting problem. A patient with

    rx of:

    plano -1.00 x 175
    plano - 1.00 x 165 2.5 base up
    +2.50 add ou

    st 28

    Due to Graves disease and changes in medication this patient now requires the above rx with od 4 base down and os 4 base up. This may be temporary and I was wondering if I could place Fresnel prism over the existing prism in this patient's glasses. I have never used Fresnel ou before. I realized this would not be an ideal solution but would it work temporarily while her medications are adjusted?

    Thanks for all input!
    Quote Originally Posted by DragonLensmanWV View Post
    Can you just add all of it to the OD? Just one Fresnel that way.
    Right, or all to the OS.

    If the new Rx of eight prism diopters reflects an increase over the existing 2.5^, then you can place a 5.5^ fresnel on the right lens base down, or on the left lens base up. If the new prism is in addition to the present 2.5^, then it would be an 8^ base down fresnel prism on the right lens or base up on the left lens.

    The vertical prism will displace the wearer's lines of sight, and consequently the eye position towards the prism's apex by about .3mm per diopter of prism. Hence the right seg will now be about 2.5mm lower than the left seg. One might neutralize some of this height disparity by temporally raising the right side of the frame slightly. Adjust the seg heights accordingly when you replace the fresnel with surfaced prism, and account for the induced prism when decentering (note the powers at ninety degrees- raising the right seg 1.25mm induces .125^ BD, raising the left 1.25mm induces .125^ BU, so subtract about .25^ from the prescibed prism).
    Roberts Optical Ltd.
    Wauwatosa Wi.
    www.roberts-optical.com
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    Experience is the hardest teacher. She gives the test before the lesson.



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    Have found in a lot of folks that the ventian blind effect of monocular Fresnel is far more maddening than a more ballanced effect. Might even give them more of a tendancy to supress the Fresnell Pastered eye.

    Chip

  9. #9
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    But won't it make the patient look kool like those funky shades?

  10. #10
    Master OptiBoarder OptiBoard Gold Supporter DragonLensmanWV's Avatar
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    I had a neighbor that, due to an aneurism presssing on another vessel, suffered the more or less death of his nasal eye muscle so his eye turned ever increasingly inward. We at first ground prism into his lenses until the amount got too much. We then went to Fresnels and ended up eventually with the maximum 40D. A neuropthalmologist determined she could help and operated and brought his eye back out. But it didn't keep and after a year or so he was back to 40D and it wasn't enough, so he just had to patch that eye. It was turned in further than any others I'd seen.
    DragonlensmanWV N.A.O.L.
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  11. #11
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    Wow!,

    Thanks for all the great replies. I really appreciate the help. I hope you all have a great Wednesday,

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