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Thread: Multifocals and aniseikonia

  1. #1
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    Multifocals and aniseikonia

    Post cataract surgery ou during which pt was set up for monovision, comes in with outside Rx from her (older age) DO (not OD) which will be her first pair of specs since surgery:

    OD Plano -0.75 x 075 Add 2.50
    OS -3.00 -0.25 x 105 Add 2.25

    I did not work with the patient initially. She was sold poly FT28 in a fairly appropriate-size frame (I can look at the records again tomorrow for exact dimensions and measurements, and Iíll see if the lab can tell me what the BCs and thicknesses were). While I was doing an adjustment for a different pt, I overheard the dispense during which the pt FREAKED. All she could say was that she ďcanít seeĒ, throws the glasses down, tries again, ďcanít see anythingĒ, glasses down, back on, ďI just canítĒ which sounds like aniseikonia to me? Would just vertical imbalance cause this sort of nonspecific complaint and intolerance, or would it be diplopia if it were the VI issue? Itís probably pertinent to note that she was fine while closing either eye.

    I was able to at least glean the above info re: her history while I finished my adjustment (of course none of this info was obtained by the optician during the initial encounter), but I wasnít able to sit and troubleshoot like I wanted to. The pt was poíd and just stormed out saying she is going straight back to her doctor, and the optician working with her didnít ask any questions at all to try to get more info about what she was experiencing or why her dr is neutralizing the monovision, etc. And I wasnít able to pay enough attention to see if it was the near only or both near and far.

    Anyway, my questions are these:
    1) How do/would I know if it was both aniseikonia AND VI?
    2) If itís both, would our only option (besides contacts) be SV? Are there any multifocals at all that could be iseikonic and also account for vertical imbalance? If so how do you calculate magnification of the seg and/or slab off?
    3) If itís only VI, would slab off suffice?
    4) What is the typical threshold for magnification difference causing aniseikonia in this type of situation (sudden change d/t cataract surgery)?
    5) What is the lower add power OS supposed to accomplish? Was that an attempt at compensating for VI?? I spoke to the DOís office to get more info but they had no idea what I was talking about; all they could tell me was the different add powers OD/OS were correct, and that they had no record of any previous glasses, and that ďmaybe she had amblyopiaĒ. Ugh.
    6) Is it normal to set one up with monovision with an extra 3.00 D plus power in the near eye? If with the monovision her near focal distance is just too short for her, is there any chance that using the above Rx except change OS sphere power to -0.50 would work? (Hypothetically of course! I know thatís not up to me. Just wondering about the concept.)

    Can someone wise explain all this to me?

    Thank you sooooooooo ridiculously much!!

    P.s. Can someone also explain to me why VI is a thing for FT28s when the lens has a distance OC AND a seg OC? My brain is just all over the place and it wonít rest until I have a good grasp on these concepts! Also, If Iím wrong on anything Iíve written, please tell me! :)

  2. #2
    One eye sees, the other feels. OptiBoard Gold Supporter
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    Would just vertical imbalance cause this sort of nonspecific complaint and intolerance, or would it be diplopia if it were the VI issue?
    There may be VI at distance. Determine the amount. There will be VI at near if multifocal (excluding different segment styles). Determine the amount.

    The best way to approach this and similar complex RXs is to trial frame to determine if there is discomfort in the primary gaze (wear for 5 minutes or so) and if there is diplopia at near during the down gaze. If you have size lenses, try +2% over the spectacle lens corrected left eye. If not, and if you have biconvex/biconcave trial lenses, you can make size lenses by piggybacking equal powers for 1% up to about 7%, the latter with the thicker, steeper curved Ī 20 D trials.

    Itís probably pertinent to note that she was fine while closing either eye.
    There is no differential prism when looking through only one eye. One solution is to occlude one of the eyes though.

    I was able to at least glean the above info re: her history while I finished my adjustment (of course none of this info was obtained by the optician during the initial encounter), but I wasnít able to sit and troubleshoot like I wanted to. The pt was poíd and just stormed out saying she is going straight back to her doctor, and the optician working with her didnít ask any questions at all to try to get more info about what she was experiencing or why her dr is neutralizing the monovision, etc. And I wasnít able to pay enough attention to see if it was the near only or both near and far.
    I wonder if the surgeon can justify what they did to their client, maybe a history of full monovison with CLs?

    Consumers- talk to your optician before the IOLs are ordered by the surgeon. Avoid monovison, multifocal implants, ask for monofocal implants with no more than 1 D of mono, consider toric lenses and relaxing incisions as needed for astigmatism.


    Anyway, my questions are these:
    1) How do/would I know if it was both aniseikonia AND VI?
    As noted above.

    2) If itís both, would our only option (besides contacts) be SV? Are there any multifocals at all that could be iseikonic and also account for vertical imbalance? If so how do you calculate magnification of the seg and/or slab off?
    No, yes, and...

    https://download.lww.com/wolterskluw...01629_SDC1.pdf

    http://assets.markallengroup.com/art...images/b2b.pdf

    3) If itís only VI, would slab off suffice?
    Yes. Minimize VI in the primary (straight ahead) gaze, then work the near gaze.

    4) What is the typical threshold for magnification difference causing aniseikonia in this type of situation (sudden change d/t cataract surgery)?
    Rule of thumb 1% for asthenopia, 5% for diplopia. YMMV.

    5) What is the lower add power OS supposed to accomplish? Was that an attempt at compensating for VI?? I spoke to the DOís office to get more info but they had no idea what I was talking about; all they could tell me was the different add powers OD/OS were correct, and that they had no record of any previous glasses, and that ďmaybe she had amblyopiaĒ. Ugh.
    Maybe the distance OS was cut a quarter, compensated for at near by cutting the add a quarter.

    No record of corrective lenses? Amblyopia? Can you say ****storm?

    6) Is it normal to set one up with monovision with an extra 3.00 D plus power in the near eye? If with the monovision her near focal distance is just too short for her, is there any chance that using the above Rx except change OS sphere power to -0.50 would work? (Hypothetically of course! I know thatís not up to me. Just wondering about the concept.)
    Not normal, or recommended. Reducing the OS distance is one possible solution, pretty far down the list of towards the poorer solutions, close to occluding one eye.

    Can someone wise explain all this to me?
    Done.

    Thank you sooooooooo ridiculously much!!
    Your welcome.

    P.s. Can someone also explain to me why VI is a thing for FT28s when the lens has a distance OC AND a seg OC? My brain is just all over the place and it wonít rest until I have a good grasp on these concepts! Also, If Iím wrong on anything Iíve written, please tell me! :).
    There can be additional VI at near due strictly to the segment OC if the add powers are dissimilar, but a .25 D differential is insignificant. Edit- dissimilar segment styles can introduce additional VI at near, but dissimlar add powers generally have no effect on VI at near.

    Best regards,

    Robert Martellaro
    Last edited by Robert Martellaro; 10-04-2018 at 06:56 PM.
    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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