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Thread: Applying Fresnel Prism to prog

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    Applying Fresnel Prism to prog

    Hi all,
    I need to apply a Fresnel prism to a prog lens 10D, split. Can you do this? Only done this with FT. He only needs the prism for near and actually we are trying something out and will probably end up ordering ground in prism. But for the time being we would like to see how he does with it. So, applying to near in a progressive... how would one do that? TIA.

    Paula K
    ~Follow Your Bliss~

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    Doh! braheem24's Avatar
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    Ideally you never split fresnel unless you're doing it for hemianopia.

    Apply prism at the lower lid in the non dominant eye only, Don't ruin his acuities in both eyes with the poor optics from a stick on.

    PS, You cant grind in 10D Prism at near on a progressive.

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    Quote Originally Posted by braheem24 View Post
    Ideally you never split fresnel unless you're doing it for hemianopia.

    Apply prism at the lower lid in the non dominant eye only, Don't ruin his acuities in both eyes with the poor optics from a stick on.

    PS, You cant grind in 10D Prism at near on a progressive.
    But that shouldn't be a problem in a trifocal, then? I don't know that he will want to give up the progressive, he's a difficult patient with extremely VAGUE complaints. However, our docs found he took 20D of prism, but no double vision without, it's a very unusual case. I believe it's a convergence issue and/or getting his eyes to work together at near. He's a moderate hyperope, +2.00OD +2.75OS with quarter cyl. 2.50ADD. We will try the press on at the lid and see what that does. Thanks.
    ~Follow Your Bliss~

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    Master OptiBoarder optical24/7's Avatar
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    You'd be hard pressed with any multi-focal to induce prism at near only in the amount your wanting. What direction is the prism? If it's horizontal, you can use a FT 45 and decenter in or out 20mm's each lens to create 5 out/in per eye. If it's vertical you'd have to use bi-centric grinding (slab off) but I don't think you'll be able to get 10 D prism up in a single lens. You could do it vertically with a reverse slab in one eye and a conventional slab in the other. ( But again, I don't know if Younger makes a reverse slab lens w/5 D of prism, plus they are available only in CR in a ft 28).

    You could also do a Franklin bifocal with deferring amounts of prism in near only ( it would be one ugly mofo though..) The better scenario would be a separate SV reading only with the amount of prism needed.




    Brah, what scenario would you split Fresnels on a hemianope? ( unless you are talking about putting a Peli type on both lenses.)

  5. #5
    What's up? drk's Avatar
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    That's got to be what brah's saying.

    As to the original diagnosis and treatment, man, that's barking up the wrong tree.

    A longstanding non-converger like that is not going to magically respond to prism at this late stage. But go ahead and waste time trying it. (I'm sure I have, before.)

    Think about this...most people only need to converge about 15^ to read, period. This guy is 20 exo, meaning he doesn't want to converge AT ALL. Plus he'll have a distance exophoria, as well, at 20 exo (at least 5 exo).

    All absolute presbyopes are high, high exophores anyway. He's not that special.

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    [QUOTE=optical24/7;529153

    The better scenario would be a separate SV reading only with the amount of prism needed.
    [/QUOTE]

    +1 agreed

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    Doh! braheem24's Avatar
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    Quote Originally Posted by optical24/7 View Post
    Brah, what scenario would you split Fresnels on a hemianope? ( unless you are talking about putting a Peli type on both lenses.)
    Split was Assumed by my run on sentence. Still working on my spanglish.

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    Quote Originally Posted by mervinek View Post
    +1 agreed
    Going with Reading glasses, he doesn't like it but has to. He knows he will use his progressives for spot reading only.
    ~Follow Your Bliss~

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