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Thread: Manipulating equithin in a digital progressive to alleviate imbalance in the near

  1. #1
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    Manipulating equithin in a digital progressive to alleviate imbalance in the near

    Hello Opti-boarders, I have an interesting patient. I will start with his rx.
    First Time Pal Zeiss Individual 2
    OD +1.75-2.25x005 Add +2.00 BC 6.00
    OS +2.25-1.50x180 Add +2.00 BC 7.00
    PD 32.5/31.5 Seg ht 21 OU (I will need to raise the OS seg to 23)
    Material: Polycarbonate

    OC's line up horizontally. He is experiencing pulling and headache noticed in his right eye. He is experiencing about 1.25 BU OS currently. I know that he really shouldn't need slab off but his symptoms seem to match. I can't get a slab off in a digital progressive from the VSP lab I had to use. So I am thinking of manipulating the equithin to alleviate some of the prismatic imbalance at near. When I raise the seg I will add another .5 diopters of vertical prism which the doctor has okayed putting prism in the distance part of the glasses to cancel that. Does this seem reasonable? Is there anything I might be missing? And does anyone think the slight BC difference could be playing a role? Distance vision is great. Thanks for your help.

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    One eye sees, the other feels. OptiBoard Gold Supporter
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    The powers on the vertical meridian are OD -0.50 D and OS +0.75 D, for a difference of 1.25 D. The Zeiss lens has a 6mm drop, inducing 0.75∆ of Vertical prism Imbalance Base Up OD (or BD OS) at the distance point, and roughly 1.00∆ VI BD OD (or BU OS) at near, if the near point is 8mm below the PRP. Hence, any attempt to introduce a global prism to minimize VI at near will increase VI on the distance gaze!

    The by the book solution, if we want to eliminate VI at both far and near is to introduce a canceling prism (0.75∆ BD OD (or 0.75∆ BU OS ), and use a 1.75∆ base up slab OD.

    However, this degree VI in healthy eyes rarely causes symptoms. I would look elsewhere, probably normal adaptation, task glasses, etc.

    Hope this helps,

    Robert Martellaro
    Roberts Optical Ltd.
    Wauwatosa Wi.
    www.roberts-optical.com
    ~~~~~~~~~~~~~~~~~~
    Science is a way of trying not to fool yourself. - Richard P. Feynman

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    Master OptiBoarder optical24/7's Avatar
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    There shouldn't be 1.25 D vertical imbalance with only a +.75 difference in power at 90. Did you check prism imbalance at the PRP? I say they are made incorrectly.
    Last edited by optical24/7; 05-21-2019 at 01:55 PM.

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    A few questions:

    1. What can you tell us about his history? How has his Rx changed over time?

    2. Being a first PAL wearer, and given that you've fit him into a digital PAL, has he worn a digital SV before?

    3. Is this a new frame in addition to new lenses? If so, are there any drastic shape/size/POW changes from his previous pair?

    Also, remember that if you raise his OC, you're going to draw unwanted astigmatism present in the lens closer to his natural line of sight. In my experience, most hyperopes (honestly, most new PAL wearers in general) hate this, so tread carefully.

    I'm with Robert, I don't think prism and prism thinning are the best place to start looking to fix his issue. I'd be looking at adaptation first, then Rx and glasses history second, and prism a far distant third.

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    Quote Originally Posted by optical24/7 View Post
    There shouldn't be 1.25 D vertical imbalance with only a +.75 difference in power at 90. Did you check prism imbalance at the PRP? I say they are made incorrectly.
    What he said.

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    One eye sees, the other feels. OptiBoard Gold Supporter
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    Quote Originally Posted by optical24/7 View Post
    There shouldn't be 1.25 D vertical imbalance with only a +.75 difference in power at 90. .
    Brain freeze! Too much vacation fun!

    Quote Originally Posted by bretk0923 View Post
    In my experience, most hyperopes (honestly, most new PAL wearers in general) hate this, so tread carefully.
    Emerging presbyopic hyperopes! I don't want to seem them until they're age 60.

    Robert
    Roberts Optical Ltd.
    Wauwatosa Wi.
    www.roberts-optical.com
    ~~~~~~~~~~~~~~~~~~
    Science is a way of trying not to fool yourself. - Richard P. Feynman

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    Master OptiBoarder CCGREEN's Avatar
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    Reverse the base curves. Put the 7 on the right Rx and the 6 on the left Rx. Just something I learned at ED hrs one time way back in my other life it. It always seems to resolve the problem for me.

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    Thank you everyone for your responses.

    He did not have a current pair of glasses except +1.75 OTC readers. His previous refraction was similar but he did not fill it. He is doing great in the distance and reading well out of the OS. But having problems OD near. He says he feels like his eye are not working well together, with a pulling sensation OD. Uncorrected VA's 20/40od 20/80 OS Corrected 20/20 OU. His pupils are unequal in height but he was ordered with equal seg heights.
    Last edited by jasons; 05-21-2019 at 03:33 PM.

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    Quote Originally Posted by Robert Martellaro View Post
    Brain freeze! Too much vacation fun!

    Emerging presbyopic hyperopes! I don't want to seem them until they're age 60.

    Robert

    ain't no emerging presbyope with a 2.00 add this patient was in denial. I'm with bret on this one. Study the patient history. What were they wearing before? How was it fitting? You may be perfect in your measurements but their old glasses would be wack and they got used to it.

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    Master OptiBoarder optical24/7's Avatar
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    Quote Originally Posted by Robert Martellaro View Post
    Brain freeze! Too much vacation fun!

    Emerging presbyopic hyperopes! I don't want to seem them until they're age 60.

    Robert
    Your brain is fine Robert, it’s I that had to much vacation fun! You were correct, 1.25 imbalance. Saying that, you are also correct that a 1.25 imbalance is seldom an issue, closer to 2.00 and up are slab concerns.

  11. #11
    One eye sees, the other feels. OptiBoard Gold Supporter
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    Quote Originally Posted by jasons View Post
    Thank you everyone for your responses.

    He did not have a current pair of glasses except +1.75 OTC readers.
    My optical heart sinks like a rock in quicksand. I feel for you, but have little to offer but hopes and prayers.

    His previous refraction was similar but he did not fill it. He is doing great in the distance and reading well out of the OS. But having problems OD near. He says he feels like his eye are not working well together, with a pulling sensation OD. Uncorrected VA's 20/40od 20/80 OS Corrected 20/20 OU. His pupils are unequal in height but he was ordered with equal seg heights.
    You will want to fix that.

    Hope this helps,

    Robert Martellaro
    Roberts Optical Ltd.
    Wauwatosa Wi.
    www.roberts-optical.com
    ~~~~~~~~~~~~~~~~~~
    Science is a way of trying not to fool yourself. - Richard P. Feynman

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