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Thread: chromatic aberation

  1. #1
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    chromatic aberation

    I have a patient who is a Current progressive wearer with basic poly. She got a frame with a much bigger B measurement and was having problems with things swimming and seeing a blue and green line top and bottom of objects ....only in the 10 to15 foot rang ... Not happening at extreme distance!!!

    I reduced the size of the frame selecting a smaller B measurement and set progressive start to exactly where old pair does. Still having same issue. Rx is O. D. +4.00 O. S. +2.00 with 2.00 add.

    Says when she tips her head way back things are "good"

    A bit baffled.....

    Any thoughts are appreciated!!!
    Last edited by cvbs; 10-27-2014 at 07:06 PM.

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    What lens she in now? At a +4 I'd say put her in at least 1.60, 1.67 preferably. Both have a better ABBE value than poly and will have a better base curve. I'd be willing to bet that when she tilts her head back she is not getting the refraction on the edges of the lenses.
    Not sure what she paid for but I'd put her in a Auto 3 or InTouch to get a lower BC (though any free form should do the trick I'm just going on what I know), high index for even better BC, and a very good AR. That should take care of it.
    The other thing it could be is bevel placement. If it's done at 50% or even moved to the front more and she have a high BC (I'm guessing +7 or +8) that could cause it to.

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    Compulsive Truthteller OptiBoard Gold Supporter Uncle Fester's Avatar
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    Read this article-

    http://www.opticampus.com/cecourse.p...ic_aberration/

    Excellent site! If you haven't already bookmark it and read the courses.

    What's the lens design?

    You may actually be able to see this too if you look through the glasses.

    Also from a past thread-

    http://www.optiboard.com/forums/show...object-borders

    Prism thinning is probably the issue.
    Last edited by Uncle Fester; 10-28-2014 at 10:38 AM.

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    OptiBoard Novice KiaABOC's Avatar
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    I wouldn't suggest a larger corridor PAL. I would suggest a short corridor PAL with a very good visual performing anti-reflective coating. This way she should not have problems finding the focus point and the blue and green prismatic effect should disappear. Also, a mid-index or high-index lens should be used.
    Lakia Renee Sellman, A.B.O.C.

  5. #5
    One eye sees, the other feels OptiBoard Silver Supporter
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    Quote Originally Posted by cvbs View Post
    I have a patient who is a Current progressive wearer with basic poly. She got a frame with a much bigger B measurement and was having problems with things swimming and seeing a blue and green line top and bottom of objects ....only in the 10 to15 foot rang ... Not happening at extreme distance!!!

    I reduced the size of the frame selecting a smaller B measurement and set progressive start to exactly where old pair does. Still having same issue. Rx is O. D. +4.00 O. S. +2.00 with 2.00 add.

    Says when she tips her head way back things are "good"

    A bit baffled.....

    Any thoughts are appreciated!!!
    The head tilt adds plus, and depending on the degree of tilt, decreases induced prism. Confirm the Rx and consider the use of a less dispersive material.

    Quote Originally Posted by KiaABOC View Post
    I wouldn't suggest a larger corridor PAL. I would suggest a short corridor PAL with a very good visual performing anti-reflective coating. This way she should not have problems finding the focus point and the blue and green prismatic effect should disappear. Also, a mid-index or high-index lens should be used.
    The symptoms appear to be on the primary gaze, making it unlikely that changing the corridor length will have any positive effect.

    Unfortunately, AR coatings do not reduce chromatic aberration.
    Science is a way of trying not to fool yourself. - Richard P. Feynman

    Experience is the hardest teacher. She gives the test before the lesson.



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    Compulsive Truthteller OptiBoard Gold Supporter Uncle Fester's Avatar
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    Robert- My first thought was polycarbitis as well but if both are poly why one and not the other?

  7. #7
    One eye sees, the other feels OptiBoard Silver Supporter
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    Quote Originally Posted by Uncle Fester View Post
    Robert- My first thought was polycarbitis as well but if both are poly why one and not the other?
    We don't have all the data so all we can do is speculate.

    One possibiity is a change in lens design. Specifically, the distance from the fitting point to the PRP, for example, Seiko is usually zero, Zeiss usually 6mm, and/or differences in prism thinning. cvbs may feel that a Zeiss type lens is best for the client; increasing the Abbe may allow that to happen without compromise.
    Science is a way of trying not to fool yourself. - Richard P. Feynman

    Experience is the hardest teacher. She gives the test before the lesson.



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    I have had three patients that saw a yellow highlight around objects and/or text. All of them were in zeiss gt2 3d or individual 2. In two instances, the problem was solved by switching material (Poly->CR39, Poly->1.67) and in one instance I changed frame/lens to Shamir auto II and a less round lens shape(the lens was rotating in original frame choice which was compounding problems).

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