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Thread: How do progressive designs deal with vertical imbalance caused by astigmatism at 90?

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    How do progressive designs deal with vertical imbalance caused by astigmatism at 90?

    Hey all!

    We have a client that has a distance and near rx:

    Dist
    +1.50 +0.50 *090
    -2.50 +4.00 *095


    Near
    +2.50 +0.50 *090
    -0.75 +4.00 *095

    She's tried progressives before but said that she could not get used to them. At first, I thought that this might be a combination of poor expectation-management and or bad measurements/lens design. But upon analyzing the rx my coworker realized that there is a substantial amount of vertical imbalance taking place close to the 90 degree meridian. He calculated about 3+ diopters of prism at 10mm(which is generous considering that the reading seg would be even lower). This, including any size difference, may be the reason that she had trouble adapting... but we simply don't know. Do modern progressives have some way to deal with and assuage this imbalance?

    Thank for any help!

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    Master OptiBoarder optical24/7's Avatar
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    The imbalance is more like 4 diopters. Labs “deal with it” by grinding slab-off prism ( on the most minus/least plus lens). Though they can be ground on a PAL, expect patient dissatisfaction most of the time. In fact I’ll let them go be disappointed somewhere else before I do another. Ft bi or tri’s are all I do anymore.

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    Master OptiBoarder AngeHamm's Avatar
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    Quote Originally Posted by Jaketull View Post
    Hey all!

    We have a client that has a distance and near rx:

    Dist
    +1.50 +0.50 *090
    -2.50 +4.00 *095


    Near
    +2.50 +0.50 *090
    -0.75 +4.00 *095

    She's tried progressives before but said that she could not get used to them. At first, I thought that this might be a combination of poor expectation-management and or bad measurements/lens design. But upon analyzing the rx my coworker realized that there is a substantial amount of vertical imbalance taking place close to the 90 degree meridian. He calculated about 3+ diopters of prism at 10mm(which is generous considering that the reading seg would be even lower). This, including any size difference, may be the reason that she had trouble adapting... but we simply don't know. Do modern progressives have some way to deal with and assuage this imbalance?

    Thank for any help!
    We kind of need to know what kind of progressive your patient non-adapted to be able to speak intelligently. At least, how long ago it was. Modern digital progressives will be much better at compensating for this than even lenses from seven or eight years ago, but remember that Ryser's Rule is definitely in play here: they need to be motivated to adapt in order to adapt.
    I'm Andrew Hamm and I approve this message.

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    You need to know if this is fusion related and/or swim related. This PX may not be a PAL candidate even with a slab. Most labs will not automatically slab this RX without reaching out to you first
    I bend light. That is what I do.

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    Anisometropic patients are always tricky. Yes, there are tons of other "things" that could cause issues with regard to Rx, etc. HOWEVER, most of them have to do with (as everyone says) image size differences and prism imbalance.

    I'm not sure about the analytics behind prism thinning (the lab gurus can give more insight into that), but as a dispensing optician I can tell you that a lot of the new PALs that have arrived onto the scene lately seem to work pretty well in dealing with this specifically.

    I had dispensed a pair of glasses to a patient who was post-IOL surgery in one eye only that had about 5 diopters of aniso, and she adapted perfectly to HOYA's new Array 2 lens. That's probably the most extreme case of aniso in a PAL that I've ever had, and we did not have to use slab-off. According to the HOYA sales rep, the new tech in the Array 2 and also in the new ID Lifestyle 3 lenses is called Binocular Harmonization Technology, designed specifically to eliminate exactly the issues that come up with differences in Rx between lenses. He didn't go into further detail beyond that, but I didn't have any issues with that particular patient.

    I've also dispensed the IDLS3 lenses to patients with 2-3 diopters of aniso and had plenty of success without slab-off. I've also dispensed Shamir's new Autograph Intelligence lenses in similar situations without trouble.

    All that being said, I agree with AngeHamm. Never forget Ryser's Rule. In all of my situations, I got my patients excited about PALs before dispensing them. They were all motivated to try them, with a very good understanding of the limitations and pitfalls they might expect to arise in their unique situations.

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    Master OptiBoarder optical24/7's Avatar
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    I don’t care how modern a PAL you use, optics are optics. The pt has 4D of vertical imbalance. You can prism thin all you want, or put the oc’s At the PRP, (Prism reference point), there will be prismatic imbalance vertically everywhere except at the PRP.

    Lets say they use no prism thinning on a 4 drop PAL. At the fitting cross you would have 1.6D of vertical prism imbalance. Below the PRP 4 mm you’ll have 1.6D prism imbalance the opposite direction. If the patient is viewing at reading level, approximately 10mm below the PRP they will experience 4D of vertical imbalance. I’ve never seen a patient that can handle 4D of vertical imbalance at near that had binocular vision, ( let alone 5D of imbalance). If you were successful I can almost assure you the patient had/and or developed a monocular reading habit.

    It makes no difference old design, modern design PAL, bifocal or trifocal, you are not going to have binocular vision in any multi-focal at near with 4D of imbalance without bicentric grinding (slab-off).

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    What's up? drk's Avatar
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    Yeah, that's a heavy lift.

    It's helpful to know what the patient's binocular status is. How are they coping with that mess? If they've had a vertical imbalance a long time, without trouble, either they have a killer optician or they are suppressing one eye's central vision.

    If they've had a sudden change (like cataract surgery) that creates the anisometropia, you're in big trouble because they aren't going to adapt.



    As to remediation, big aniso's like that don't scream for a PAL. I've never slabbed one. I guess you could try that with a short corridor. I will say that some of the newer "symmetry" designs and "design by prescription" and all that binocular smoothing stuff is probably somewhat helpful.

    Alternatively, if money is no object, the Shaw Lens would be a possibility.

    But the traditional way is a segmented MF with a slab-off.

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    One eye sees, the other feels. OptiBoard Gold Supporter
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    Hi Jaketull,

    Verify the unequal adds. Check the acuity and/or discuss with the prescriber.

    If the Old Rx has a similar power disparity at ninety, mask the distance zone of the old eyeglasses with painters or masking tape down to about 4mm above the anticipated near zone.

    Using flippers or trial lenses over to remove blur, have the client look at the reading card to establish the degree of discomfort or diplopia. Otherwise use a trial frame and perform the same test.

    If diplopia, consider slabbed segmented multifocals, SVNO, or Chemistrie clips.

    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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    Doc, once again, modern, digital designs can’t do jack for a 4D vertical imbalance! ( without some type of bicentric grinding...)

    If, if you were going to a design a lens that addressed this without bicentric grinding, you would have to have a lens that progressively increased/decreased the prismatic as you go down the lens to the near area. Interestingly, about 10 years ago, I was corresponding with Darryl and Harry C on producing such a design, if it was possible. The final conclusion was that it would need to be designed similar to a PAL, with a corridor and umbilic to manage the induced (and progressive) horizontal cylinder produced (and increased) through the design.

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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
    Lets say they use no prism thinning on a 4 drop PAL. At the fitting cross you would have 1.6D of vertical prism imbalance.
    Yes, and that induced VI in the primary gaze is often overlooked, resulting in asthenopia. For example, my older eyes can barely fuse 1 D of VI, 2 D is diplopia. Splitting the VI between near and far with multifocals might be successful with less VI, but it's unlikely I could wear a pair of eyeglasses with that much vertical prism imbalance.

    If the client wants progressives for cosmesis, with some intermediate utility (instrument cluster, shopping/shelves etc.), I could add prism to cancel the induced VI in the primary gaze, or use a PAL design with zero drop (Seiko?). Separate eyeglasses would be required for extended near tasks of course.

    Quote Originally Posted by optical24/7 View Post
    Doc, once again, modern, digital designs cant do jack for a 4D vertical imbalance! ( without some type of bicentric grinding...)
    IME, the dumber the lens, the easier it is to make it work when the going gets tough (6 D cyls, prescribed prism, etc.).

    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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    What's up? drk's Avatar
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    Quote Originally Posted by optical24/7 View Post
    Doc, once again, modern, digital designs cant do jack for a 4D vertical imbalance! ( without some type of bicentric grinding...)

    If, if you were going to a design a lens that addressed this without bicentric grinding, you would have to have a lens that progressively increased/decreased the prismatic as you go down the lens to the near area. Interestingly, about 10 years ago, I was corresponding with Darryl and Harry C on producing such a design, if it was possible. The final conclusion was that it would need to be designed similar to a PAL, with a corridor and umbilic to manage the induced (and progressive) horizontal cylinder produced (and increased) through the design.
    Sure, I'm not disagreeing.

    Although Shaw he use some voodo optics, mon. He be laughing at Prentice's Rule.

    But you have to say that modern PALs like the Auto Intelligence has at least a 10% chance of working, whereas an old mono design would have, say, 1% chance.

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    Master OptiBoarder optical24/7's Avatar
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    Dr. Shaw has made a tremendous advance in lens design, specifically for Aniseikonic lenses but, it’s not voodoo. He simply (not too simply programmed) took known formulas and built a computer program to design lenses with the best binocular vision. In his patent he states he uses the standard magnification formula, (1/(1-t(n)(F1)x1/(1-dV(Fv).

    The design uses the classical base curve, lens thickness, material and vertex to reduce Aniseikonia. As far as prismatic comps for VI or HI, the designs works by pushing and measuring the individuals prismatic tolerance. The prescriber measures tolerances to prism both + and - vertically and horizontally. ...

    The big differences in Dr Shaw’s lens designs is 1. Prism tolerance by the individual patient, both horizontal and vertical. 2. Ability to vary corridor length based on power and prismatic induced eye displacement due to prism. 3. Ray tracing all of this and fabricating.

    Using Robert as an example, he says he can tolerate about 1D of vertical and maintain fusion. (If I understand it), the Shaw design would produce 1D of base up in the OD at distance, and 1D of base down OD at near. This particular patient should be able to maintain fusion at both near and far. If we were to do this to Robert ( I know your not) he’s obviously Aniseikonic, and the design would also have differing base curves, thicknesses, indexes, vertex and corridor length.

    Extremely advanced. Revolutionary in design....Voodoo...I don’t think so...
    Last edited by optical24/7; 06-24-2019 at 09:07 PM.

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    Quote Originally Posted by optical24/7 View Post
    Dr. Shaw has made a tremendous advance in lens design, specifically for Aniseikonic lenses but, its not voodoo. He simply (not too simply programmed) took known formulas and built a computer program to design lenses with the best binocular vision. In his patent he states he uses the standard magnification formula, (1/(1-t(n)(F1)x1/(1-dV(Fv).

    The design uses the classical base curve, lens thickness, material and vertex to reduce Aniseikonia. As far as prismatic comps for VI or HI, the designs works by pushing and measuring the individuals prismatic tolerance. The prescriber measures tolerances to prism both + and - vertically and horizontally. ...

    The big differences in Dr Shaws lens designs is 1. Prism tolerance by the individual patient, both horizontal and vertical. 2. Ability to vary corridor length based on power and prismatic induced eye displacement due to prism. 3. Ray tracing all of this and fabricating.

    Using Robert as an example, he says he can tolerate about 1D of vertical and maintain fusion. (If I understand it), the Shaw design would produce 1D of base up in the OD at distance, and 1D of base down OD at near. This particular patient should be able to maintain fusion at both near and far. If we were to do this to Robert ( I know your not) hes obviously Aniseikonic, and the design would also have differing base curves, thicknesses, indexes, vertex and corridor length.

    Extremely advanced. Revolutionary in design....Voodoo...I dont think so...
    Definitely not voodoo, but is also not that proprietary considering almost any lab with FF capabilities can produce lenses with aniseikonic correction for a small additional charge, instead of the astronomical Shaw upgrade.

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    Master OptiBoarder AngeHamm's Avatar
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    Quote Originally Posted by drk View Post
    But you have to say that modern PALs like the Auto Intelligence has at least a 10% chance of working, whereas an old mono design would have, say, 1% chance.
    Yes sir.
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    Voodoo is good.

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    Quote Originally Posted by Lab Insight View Post
    Definitely not voodoo, but is also not that proprietary considering almost any lab with FF capabilities can produce lenses with aniseikonic correction for a small additional charge, instead of the astronomical Shaw upgrade.
    Tell us more. I was unaware of this.

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    One eye sees, the other feels. OptiBoard Gold Supporter
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    Quote Originally Posted by drk View Post

    But you have to say that modern PALs like the Auto Intelligence has at least a 10% chance of working, whereas an old mono design would have, say, 1% chance.
    Each image might be 10% clearer, but there would still be two images. In some cases, old school semi-finshed PALs work even better, so don't throw away your old vinyl and CDs quite yet.

    Quote Originally Posted by optical24/7 View Post
    Using Robert as an example, he says he can tolerate about 1D of vertical and maintain fusion. (If I understand it), the Shaw design would produce 1D of base up in the OD at distance, and 1D of base down OD at near. This particular patient should be able to maintain fusion at both near and far.
    Using Remole's equations, the VI at near is neutralized or minimized by manipulating the base curves instead of using bicentric grinding.

    However, with my -4.00 D Rx, if I had a unilateral IOL implanted, and the result was a poor -2.00 D, the Shaw lens would have one lens with a steep base curve, the other quite flat, increasing the weight with poor cosmesis, and unless the software can properly compensate for these extreme curves, significant marginal astigmatism.

    Moreover, extreme manipulation of the lens shape may aggravate the disparity in retinal image size, enough to require an increase in center thickness and/or an extreme bevel placement to compensate. That's a lot of ugly shaped and positioned plastic to put on my face when, in this example, a separate pair of task eyeglasses would've met my visual needs.

    Extremely advanced. Revolutionary in design....Voodoo...I dont think so...
    Yup, science not voodoo. But when to use it requires experience. When in doubt, consult.

    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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    Master OptiBoarder optical24/7's Avatar
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    Quote Originally Posted by Robert Martellaro View Post
    Each image might be 10% clearer, but there would still be two images. In some cases, old school semi-finshed PALs work even better, so don't throw away your old vinyl and CDs quite yet....
    Thank you Robert, maybe they will listen to you. Digital FF is not magic nor is it capable of defying optics laws and facts!

  19. #19
    What's up? drk's Avatar
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    Geez, you're making too much out of this.

    The newer designs have increased depth of focus, so that helps a little, because they wouldn't have to look down as far.

    There are short corridors that are quite short. That helps a little.

    They tend to hold the near zone wider for higher adds. That helps a little.

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    Master OptiBoarder optical24/7's Avatar
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    Ahh, yea, ok. All that will *help a little* ........With 4D of vertical imbalance! Jezz!



    ( I give up!)

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