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Thread: Prescribed prism with anisometropia in a progressive

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    Compulsive Truthteller OptiBoard Gold Supporter Uncle Fester's Avatar
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    Prescribed prism with anisometropia in a progressive

    Once again I look forward to being humbled by those who can help me with this juicy piece of optics.

    Recent rx from 2/2/20 Auto 2 fixed 18mm distance vision created diplopia but near was fine:
    R -3.75 -1.00 x75
    L -6.50 -1.00 x 110
    add +2.50


    Gun-shy about how well this would work (outside MD group wrote the script) I made a s/v distance only at cost from stock 1.67 decentered to achieve prism. He's worn them for a couple of weeks and it looks like all is well. However......

    New rx to address diplopia:
    R -4.25 -1.00 x50 1^ up
    L -6.25 -1.25 x110 1^ down
    add +2.50


    Now we want to go back to the progressives but using Darryl's calculator I'm getting what will be 2.58^ prism UP in the LEFT at 15mm gaze drop. But he is wearing the current progressives for near comfortably. The old rx is creating 4^ up in the left.
    So my question is will an Auto 3 11 or 13mm compensate? I'm inclined to think not. Slab off???

    I've got to stop as once again my small room is filling with smoke...

    Last edited by Uncle Fester; 03-08-2021 at 01:29 PM.

  2. #2
    What's up? drk's Avatar
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    Just to understand...

    You made the first pair, then a second prescription came back with prism to be added??

    I'm just trying to understand...

    ...the docs thought that the guy needed vertical prism in primary gaze, I think, and they missed it the first time?

    ...they would NOT be trying to fix a vertical imbalance on downgaze (in some kind of prism-splitting adventure) because a.) the directions are opposite that, b.) patient hadn't been complaining about near gaze, so they'd leave that alone.


    So we are to assume that there is a vertical phoria, and it's antagonistic to the anisometropia (that is, looking off axis vertically will exacerbate/not help) and it will only make matters worse on downgaze. You already know this.

    The question is:
    Why no double on downgaze before? If the guy can't handle a little vertical deviation in the distance portion and goes back to complain? Where's his muscle-power? He was fusing approximately 2.5 BD OS on downgaze before.

    Are the docs on the right track? Why all of a sudden does he need prism for a measly 2^ right hypophoria? Maybe it was double vision on lateral gaze? There's 3 ansio looking left or right...hope that was ruled out.



    What I would do: trial lens.
    Last edited by drk; 03-08-2021 at 04:40 PM.

  3. #3
    One eye sees, the other feels. OptiBoard Gold Supporter
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    And is that prism due to a vertical phoria, or in response to the vertical prism imbalance generated by the 4mm drop PAL in conjunction with dissimilar powers at 90 degrees?
    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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    Compulsive Truthteller OptiBoard Gold Supporter Uncle Fester's Avatar
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    We made a progressive in February 2020 that worked well but he was feeling eye strain and decided to get just a sv distance pair, new frame, same distance rx in early January. Continued strain sent him back to the original prescriber who found the diplopia and rewrote the script with prism.

    To be safe I made a sv pair to verify (my doc for whatever reason is not a fan of trial frame/lensing) as he wanted to get progressives. These have now proved to be ok so he wants new progressives with the distance prism but I'm unsure how that's going to affect his near.

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    Compulsive Truthteller OptiBoard Gold Supporter Uncle Fester's Avatar
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    Quote Originally Posted by Robert Martellaro View Post
    And is that prism due to a vertical phoria, or in response to the vertical prism imbalance generated by the 4mm drop PAL in conjunction with dissimilar powers at 90 degrees?
    Thanks for the replies.

    Multiple past progressives never caused a problem. The diplopia started late last summer.

    His MD ruled out physical causes and his OD explained that he thought it was his older eyes wanting to get some help with prescribed prism.

  6. #6
    What's up? drk's Avatar
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    It's entirely possible that he's been able to suppress on downgaze with the vertical imbalance, before.

    I should hope he's able to suppress on dowgaze with even more vertical imbalance.

    All this can be verified with Stereo Fly.

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    Compulsive Truthteller OptiBoard Gold Supporter Uncle Fester's Avatar
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    Am I thinking right if I trial lens a 1 then 2 prism base up diopter lens over his old pair progressive left lens at near?

    Would this simulate what I'd be making in a new progressive pair?

    Thanks again.

    I'm off tomorrow and will check back Wednesday.

  8. #8
    What's up? drk's Avatar
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    This new prism is just exacerbating the vertical imbalance on downgaze, just when everything was going swimmingly...

    I doubt if the person is fussy about a vertical phoria on primary gaze, that he'd be NOT FUSSY about reading with a 3^ vertical imbalance on downgaze all this time. But such it seems.

    I'd take his glasses that you made first without prism, put the prescribed prism in front of one eye (2^ BU OD, for example) and see if he gets double when he's using the progressive. If not, life is good. (Trialing it at distance is probably not necessary...they say "prism" and you have to say "Yes, massah".)

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    Compulsive Truthteller OptiBoard Gold Supporter Uncle Fester's Avatar
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    Sounds like a plan and thanks again drk.

    Fingers crossed;) I'll post the result.

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    I'm looking forward to hearing how this turns out.

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    One eye sees, the other feels. OptiBoard Gold Supporter
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    Values rounded slightly.

    If 14mm reading depth

    Old at 90˚
    -4.25
    -6.50

    VI 1∆ bd rt distance
    VI 2.25 bu rt near (less 4mm drop)

    New at 90˚
    -4.75
    -6.25

    VI 0.5∆ bd rt distance
    VI 1.50 bu rt near (less 4mm drop)

    Unlikely you'll have a problem at this level of VI, maybe asthenopia at worst.

    The fitting point for the right eye should be lowered about 1mm due to the prescribed prism plus VI.

    Hope this helps,

    Robert Martellaro
    Last edited by Robert Martellaro; 03-10-2021 at 02:53 PM.
    Roberts Optical Ltd.
    Wauwatosa Wi.
    www.roberts-optical.com
    ~~~~~~~~~~~~~~~~~~
    Science is a way of trying not to fool yourself. - Richard P. Feynman

  12. #12
    What's up? drk's Avatar
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    I get:

    vertical imbalance Old glasses in downgaze~2.75 BD OS
    vertical imbalance New glasses with prism in downgaze ~3.5 BD OS

    To be clear, I'm not trying a trial prism lens to demonstrate a correcting prism amount...I want to trial lens the NEW vertical imbalance amount. So, I guess I'd grab about 1^ BD OS (which is the increased imbalance created with the new powers and prism) and put it over the existing MF (the one you made first that was double in the distance) to see what happens at near.

    Alternatively, if I'm reading it right, and you made SV in the new distance powers with prescribed prism, then you only have to have the guy look down through the bottom of the lens to see if he's double. No trial lenses needed.
    Last edited by drk; 03-10-2021 at 02:12 PM.

  13. #13
    One eye sees, the other feels. OptiBoard Gold Supporter
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    drk,

    I had my bases reversed- I hope I fixed it before the bots write it in stone.

    You're getting a lot more VI than I'm calculating- the power disparity at ninety is only 1.50 D on the new, and the distance from the PRP to the near point is unlikely to be much more than about 10mm.

    Best regards,

    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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    Quote Originally Posted by Robert Martellaro View Post
    drk,

    I had my bases reversed- I hope I fixed it before the bots write it in stone.

    You're getting a lot more VI than I'm calculating- the power disparity at ninety is only 1.50 D on the new, and the distance from the PRP to the near point is unlikely to be much more than about 10mm.

    Best regards,

    Robert
    I think Drk is saying there is an addition 2D of prescribed prism in the new Rx making it 3.50D imbalance.

  15. #15
    What's up? drk's Avatar
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    ^^^That's all I'm sayin'...

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    I'm on board with all of Drk's assessment and suggestions in this thread.

  17. #17
    One eye sees, the other feels. OptiBoard Gold Supporter
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    Quote Originally Posted by Kwill212 View Post
    I think Drk is saying there is an addition 2D of prescribed prism in the new Rx making it 3.50D imbalance.
    It's important to note that when determining the degree of VI, prescribed vertical prism should be ignored. In the above scenario, there is less VI at near (and at far) with the proposed new eyeglasses than with the old.

    Best regards,

    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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    Normally I would agree that it should be ignored as theoretically the prescribed prism should bring things back to balance, to a zero point so to say. Except in this case the patient was already asymptomatic at near, and the prism was prescribed to alleviate distance diplopia. So I think in this case I would include it for the near imbalance calculation. I'm open to be pursueded otherwise though.

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    One eye sees, the other feels. OptiBoard Gold Supporter
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    The only exception I can think of is for incomitant vertical deviations, where the deviation varies with the angle of gaze.

    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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    If the trial lens over the original progressive is inconclusive for a short trial, perhaps put a fresnell prism on the original progressive for a few days and give it a "real world" trial?

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    Compulsive Truthteller OptiBoard Gold Supporter Uncle Fester's Avatar
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    I'm kicking myself for not realizing what the venerable drk suggested was the way to go.

    So the patient came in yesterday and was fine with a 2^up held over his current pair of no prism progressives at distance and near.

    The OD (not one of mine) who did the recent refraction told him he was purposely going with the minimum prism so it made sense that some extra at near would be fine.

    I mentioned how my now retired OD was a fan of telling all prism patients that "You don't feed the beast" when it comes to prescribed prism and go with the least amount that achieves comfort.

    I know I'll catch flack for it but I kept him in an Auto 2 15mm fixed. This was what my co worker put him in a few months ago while I would have gone with an Auto 3 originally anytime I see this kind of power difference.

    I'll let you know how it turns out in a couple weeks when the job gets dispensed.

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    Quote Originally Posted by Robert Martellaro View Post
    The only exception I can think of is for incomitant vertical deviations, where the deviation varies with the angle of gaze.

    Robert
    Yeah, I know you are right as usual. I should not have called it imbalance. You are correct in saying 1.5D imbalance. But from a practical standpoint there is more total vertical prism present in the lenses at near with the new Rx, and Drk's suggestions of a 1D trial lens would make quick work of determining patient tolerance to the new prescribed prism prior to making lenses. Obviously all of this could be avoided is the prescribing doc had send more detailed notes and instructions, or if doctors were more amenable to discussing patients like this with the dispensing optician.

  23. #23
    What's up? drk's Avatar
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    I do NOT HAVE VENEREABLE DISEASE FES!

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    Quote Originally Posted by drk View Post
    I do NOT HAVE VENEREABLE DISEASE FES!
    I personally have always wanted to be venereably diseased.

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    Compulsive Truthteller OptiBoard Gold Supporter Uncle Fester's Avatar
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    UPDATE:

    A happy ending!

    Dispensed yesterday and it is working well.

    Thanks again for all the support and suggestions.

    Optiboarders RULE!!!

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