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Thread: An issue happening just enough to make me suspicious..

  1. #1
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    An issue happening just enough to make me suspicious..

    Hey gang,
    not sure if anyone has experienced this and has a solution or even a theory. I've had a couple of patients now that seem to be having NO problem with their glasses except when they try to see their LCD clock or channel display on a device that, in every case, has been located at the same distance from them as the TV, which they can see clearly. In both cases, the patient cannot recall the color of the display. I'm beginning to suspect it is the color or frequency of the light itself when viewed through polycarbonate. So possibly some sort of chromatic abberation? We are going to remake her lenses to fix a slight and unrelated measurement issue, but I was thinking at the same time to go to maybe Trivex to clean it up as well. Thoughts?

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    Ghost in the OptiMachine OptiBoard Silver Supporter Quince's Avatar
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    Not familiar with this as a problem, but you seem to be on the right track. I would also start with material and possibly coating change.
    Have I told you today how much I hate poly?

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    Master OptiBoarder OptiBoard Silver Supporter lensmanmd's Avatar
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    Quote Originally Posted by Chris2012 View Post
    Hey gang,
    not sure if anyone has experienced this and has a solution or even a theory. I've had a couple of patients now that seem to be having NO problem with their glasses except when they try to see their LCD clock or channel display on a device that, in every case, has been located at the same distance from them as the TV, which they can see clearly. In both cases, the patient cannot recall the color of the display. I'm beginning to suspect it is the color or frequency of the light itself when viewed through polycarbonate. So possibly some sort of chromatic abberation? We are going to remake her lenses to fix a slight and unrelated measurement issue, but I was thinking at the same time to go to maybe Trivex to clean it up as well. Thoughts?
    I don't believe that this is a material issue, rather a physiological issue, perhaps a sensitivity to the yellow-green spectrum, especially in a low light environment. Maybe even some contrast sensitivity. Sure, CA might add to the difficulty, but I'm not sold on that as the primary issue. Myself, blue neon kills me at night. I can't see anything in that color spectrum clearly, and it actually hurts my eyes. CR39, TVX, Poly, all about the same. Show me that same blue during the day, and all is good.

    I would probe a bit deeper and ask your patient(s) about the color of the display that bothers them, and under what lighting condition.

  4. #4
    One eye sees, the other feels. OptiBoard Gold Supporter
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    Quote Originally Posted by Chris2012 View Post
    Hey gang,
    not sure if anyone has experienced this and has a solution or even a theory. I've had a couple of patients now that seem to be having NO problem with their glasses except when they try to see their LCD clock or channel display on a device that, in every case, has been located at the same distance from them as the TV, which they can see clearly. In both cases, the patient cannot recall the color of the display. I'm beginning to suspect it is the color or frequency of the light itself when viewed through polycarbonate. So possibly some sort of chromatic abberation? We are going to remake her lenses to fix a slight and unrelated measurement issue, but I was thinking at the same time to go to maybe Trivex to clean it up as well. Thoughts?
    Welcome to OB Chris.

    The display was very likely red. Red will focus behind the retina compared to green or blue. Adding more plus will help, but normal vision at optical infinity might be a tad soft, especially for myopes. Tell your clients it's normal, and if they're engineer types, explain why.

    http://optometrytimes.modernmedicine...-test?page=0,0

    http://www.optometrytimes.com/modern...-redgreen-test

    Hope this helps,

    Robert Martellaro
    Last edited by Robert Martellaro; 06-11-2018 at 11:38 AM.
    Roberts Optical Ltd.
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    Master OptiBoarder DanLiv's Avatar
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    Some lens makers (Essilor for sure, dunno about others yet) are including blue light control in their lens material itself, so even uncoated they produce that very slight color distortion. No idea if this is your issue, but it is a recent change in some lenses. I've only had one customer notice it enough to complain.

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    Master OptiBoarder OptiBoard Silver Supporter lensmanmd's Avatar
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    Quote Originally Posted by Robert Martellaro View Post
    Nice read. Thanks Robert.

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    Poly has more problems with chromatic abberation than any other material. They don't need poly to watch TV or any other LCD screen unless they are in danger of some kind of shrapnel hitting them hard enough to break CR-39 lenses.

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    One eye sees, the other feels. OptiBoard Gold Supporter
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    Quote Originally Posted by lensmanmd View Post
    Nice read. Thanks Robert.
    Your welcome lensmanmd. Here's more on the two types of chromatic aberration.

    http://64.50.176.246/cecourse.php?ur...ic_aberration/

    Scroll down to Axial Chromatic Aberration.

    The reason we aren't concerned with axial chromatic aberration is that our eyes inherently have about one diopter, more than we'll see in even a very strong ophthalmic lens (see the formulas in the above link).

    The only other time we will be bothered by chromatic aberration in the primary gaze is when there is prescribed prism or prism thinning, possibly resulting in image blur, depending on the degree of prism. The blur is caused by lateral chromatic aberration (see the formula and acuity chart in the above link).

    Best regards,

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

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    Master OptiBoarder MakeOptics's Avatar
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    What's the issue? Don't blame any material without first laying out your problem and coming up with a sound theory otherwise you just bias your findings and fool yourself into a solution that may not be a consistent fix should the issue pop up again in the future. Chromatic aberration is a non-issue for most prescriptions under +/- 4.00 and can be mathematically computed, you can search this forum to see how to rule it out as an issue. CA tends to be more an issue with PAL's and multi focals because they require off center viewing, even then their exist ways to mitigate the issue. Some of these issues exists in other materials as well and can be problematic their as well. Stress in a material isn't that big of an issue except in certain situations most are not relevant to the day to day dealings of fitting eye wear. The softness of the material and flexibility can be a very real variable, usually what I have found with poly when it is an issue:

    The lens is stressed along a specific axis and bends the lens if it's thin enough, this causes a from of astigmatic error to form along the meridian that combined with the prescribed astigmatic power can lead to effective astigmatic power to be increased, decreased, or the meridian shifted. Simply put bend that lens enough and you can change the power. The way to check to see if this is occurring is by using a polariscope which will show stress in the lens (all materials, poly is just easier to see because it's molded under stress in most circumstances). The fix if you do see the issue is as simple as marking the points of stress, removing the lens from the mounting and taking the lens to a hand stone to reduce stress at those points. Remount and check again, often this can correct the issue without a remake. If the lens has to be remade, before switching material I will often check the thickness to make sure it's not one of those 1.0 - 1.2mm poly's, too thin is bad news; so if all parameters are accurate and fine sometimes I will just specify the lens be made slightly thicker to prevent flexing, if the lens parameters are on the border of other issues possibly being present in the lens, then it's a good idea to swap materials just eliminate any additional variables.

    Anyway just a glimpse into another method and some hard advice to never make assumptions about any material especially one that has been as popular and widely used as poly. Poly isn't the end all be all but it isn't evil either, respect it for what it can do and avoid disrespecting it, (here's an example of when poly will bite you in the back side when you never use it)

    Client sees you and orders a lens made of trivex, your competitor offers a similar lens in poly at a significant price reduction. The prescription is low: -1.00sph OU, try as hard as you might both lenses are going to perform the same to the lay person, your's is just more expensive. Any reasoning you give can more often than not fall on deaf ears. This client can loose trust in your abilities putting you at a disadvantage.
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    OptiBoard Apprentice rmnrdi's Avatar
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    I think Richard Feynman said it best:

    "The first principle is that you must not fool yourself and you are the easiest person to fool."


    When the lens is stressed you can get Stress Induced Birefringence. Which means a lens can have multiple indices of refraction. Poly is usually effected the most. Also, it can cause pretty serious issues with polarized lenses.

    Here's a picture.

    Click image for larger version. 

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    Robert Minardi ABO-AC
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    Don't know if this is quite relevant but I was reading a mini course on blue light for a required CE and seem to recall that there are fewer blue cones in the fovea lending to lower focus of blues than other colors. found the following as a back up but not the original CE I got this from:

    https://www.osapublishing.org/josa/a...osa-57-11-1289

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