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Thread: High plus patient experiencing shadows from coma...

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    Compulsive Truthteller OptiBoard Gold Supporter Uncle Fester's Avatar
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    High plus patient experiencing shadows from coma...

    Engineer with extensive ophthalmic mathematics background feels his problems is from the 3rd order aberration coma. Is he right?

    Previous rx: R+4.00-.25x83 Left +4.50 sph add +2.00
    New rx: +4.50sph OU Add +2.00

    FT28 CR39 (insisted do to better optics) Avance AR +8.25 bc.

    Autoflex 10 57 16 b47 ed65 (same as previous frame - yes it's way too big) PD R32.5/31 L35/33

    Old seg height 16.5 new 21.5
    OC set 30 from base of frame ou.

    Center thick old @5 new 7.5mm.

    As everything is virtually the same am I correct to say that he can't have both a higher seg height and the same thickness?
    He feels off axis/peripheral vision has a halo around images/words.

    Is this what a coma issue would present?

    Thanks in advance for any thoughts/suggestions.
    Last edited by Uncle Fester; 09-18-2014 at 11:39 AM. Reason: not shadow-halo...

  2. #2
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    I'm curious why the seg height changed so radically in the same frames? Suggests a potentially different curvature and reflection pattern compared to old lenses irrespective of Rx change.

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    Compulsive Truthteller OptiBoard Gold Supporter Uncle Fester's Avatar
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    Seg change per patient request.

    Curves same both have AR.

    For the curious-
    Seidel aberrations-

    http://www.quadibloc.com/science/opt0505.htm
    Last edited by Uncle Fester; 09-18-2014 at 11:26 AM. Reason: add link...

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    I am just beginning to study higher order aberrations so my knowledge is going to be lacking here compared to others but from what I understand they are a greater concern in Progressive designs over Flat Tops.

    I believe that aberrations are more likely to occur the farther out from the optical center and due to the fact that the frame is very large and he is talking about shadows in his periphery I would speculate that his problems are more likely to be caused by the giant frame than the seg or Rx change.

    I am open to being corrected though, eager to hear what some of the more experienced optiboarders have to say.

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    Compulsive Truthteller OptiBoard Gold Supporter Uncle Fester's Avatar
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    Quote Originally Posted by D_Zab View Post
    I am just beginning to study higher order aberrations so my knowledge is going to be lacking here compared to others but from what I understand they are a greater concern in Progressive designs over Flat Tops.

    I believe that aberrations are more likely to occur the farther out from the optical center and due to the fact that the frame is very large and he is talking about shadows in his periphery I would speculate that his problems are more likely to be caused by the giant frame than the seg or Rx change.

    I am open to being corrected though, eager to hear what some of the more experienced optiboarders have to say.
    But why in one pair and not the other?

  6. #6
    One eye sees, the other feels. OptiBoard Gold Supporter
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    Lucky you.

    Marginal astigmatism is much more likely. Best form requires a +9.25 BC for this Rx so there's probably about .25 DC off-axis.

    http://www.opticampus.com/files/wave...cle_lenses.pdf

    End of page 5 (of part two).

    Clarification please. "OC set 30 from base of frame ou."


    Last edited by Robert Martellaro; 09-18-2014 at 03:26 PM.
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    Compulsive Truthteller OptiBoard Gold Supporter Uncle Fester's Avatar
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    Robert-
    He wanted the OC at the same height so there's 4mm less drop from the OC in the new pair than there was in the old pair.
    And wouldn't the old pair also have the marginal astig?

    (And thanks so much for your prompt response!)

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    One eye sees, the other feels. OptiBoard Gold Supporter
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    Quote Originally Posted by Uncle Fester View Post
    Robert-
    He wanted the OC at the same height so there's 4mm less drop from the OC in the new pair than there was in the old pair.
    As long as the OC is at the correct height, that is, .5mm below the visual axis (roughly the pupil center) per one degree of pantoscopic tilt.

    And wouldn't the old pair also have the marginal astig?
    .50 D bump in the right increases the astigmatism from about .12 D to .21 D 30 degrees off-axis. That shouldn't be a problem. There's probably a fair amount of decentration, so make sure there is sufficient dihedral/wrap tilt, or is about the same as the old, although I suppose that's nearly impossible to control with a memory metal bridge.

    If they still notice more blur or ghosting off-axis, I'd take a look at the Rx, and check the AR for flaws if they say it's more like haloing than ghosting.
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    One eye sees, the other feels. OptiBoard Gold Supporter
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    Quote Originally Posted by Uncle Fester View Post
    Center thick old @5 new 7.5mm.

    As everything is virtually the same am I correct to say that he can't have both a higher seg height and the same thickness?
    I missed this.

    It should be thinner if you went from 10mm below center to 5mm below, even with the power change, although what matters the most is the vertical OC height.

    OC set 30 from base of frame ou.
    This is the vertical OC height? Was it 25mm before? If so, that makes the old OC 1.5 below center and the new OC 3.5mm above center. The 2mm increase in vertical decentration might be enough to explain the difference in center thickness.

    Watch your vertical OC placement and pantoscopic tilt values. Best form assumes an alignment of the visual and optical axes- deviation from best form increases marginal astigmatism!
    Roberts Optical Ltd.
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  10. #10
    ATO Member HarryChiling's Avatar
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    Quote Originally Posted by Uncle Fester View Post
    Engineer with extensive ophthalmic mathematics background feels his problems is from the 3rd order aberration coma. Is he right?

    Previous rx: R+4.00-.25x83 Left +4.50 sph add +2.00
    New rx: +4.50sph OU Add +2.00

    FT28 CR39 (insisted do to better optics) Avance AR +8.25 bc.

    Autoflex 10 57 16 b47 ed65 (same as previous frame - yes it's way too big) PD R32.5/31 L35/33

    Old seg height 16.5 new 21.5
    OC set 30 from base of frame ou.

    Center thick old @5 new 7.5mm.

    As everything is virtually the same am I correct to say that he can't have both a higher seg height and the same thickness?
    He feels off axis/peripheral vision has a halo around images/words.

    Is this what a coma issue would present?

    Thanks in advance for any thoughts/suggestions.
    Halo's around objects can be spherical aberration, if those halo's are birghter on one side of and object and diffuse, blurred, and spread out on the other side that is indicative of coma.

    Either way not much you can do to change a design, no remake with less coma in the notes to the lab.

    I wouldnt even bother asking which lens has less coma since no one on a lab level will know enough to tell you, plus that is one of the least significnt aberrations to deal with if best form is achieved.

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    Compulsive Truthteller OptiBoard Gold Supporter Uncle Fester's Avatar
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    Thanks so much Robert and Harry!

    I'll be dealing with this next week as I'm off to the boy's annual Fall classic golf tournament in Ticonderoga NY through Sunday.

    Should've made clear the OC has 4mm less drop in the new pair to the seg line. I thought this might have effected thickness or is it just the higher seg height?. Patient wanted the OC to remain at the same height.
    Last edited by Uncle Fester; 09-18-2014 at 05:37 PM. Reason: clarify OC...

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    Doh! braheem24's Avatar
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    Seg height does not change the CT.

    O.C. being the same the CT should change on average 0.7mm per diopter of plus, in this case you should be around a 5.4mm CT.

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    Quote Originally Posted by braheem24 View Post
    Seg height does not change the CT.
    The lens blanks for flat tops will have fixed drop and decentration for the segment, and a change in seg height will mean a change in minimum diameter for cut out ... which will impact lens thickness.
    Trip

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    Quote Originally Posted by Trip View Post
    The lens blanks for flat tops will have fixed drop and decentration for the segment, and a change in seg height will mean a change in minimum diameter for cut out ... which will impact lens thickness.
    Change in seg height may mean a change in minimum diameter of the lens blank for going in the generator, but not for the size of the actual lens that will be edged, that would be determined by the OC only I think.

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    UF sorry I missed you - you were closed by the time I could call back. I'll try again tomorrow.

  16. #16
    OptiBoard Professional OptiBoard Silver Supporter jrumbaug's Avatar
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    Here's my 2 cents..

    If the O.C. is the same old & new, I say the center thickness should be the same old and new since we are talking about a spherical front surface. We are not talking about aspheric nor progressive on the front. I am assuming the edge thickness is the same. Naturally, a thicker edge would equal a thicker center.

    If there is a difference in thickness, I suspect there is a vertical prism difference between the two pair. I base these ideas on the "thinning prism" concepts used in progressive lens. Here's a simple test to do with the lensometer. Leave the stage the same and measure the vertical prism reading on each pair at about 30mm. I suspect you will find a difference, if not, my ideas are wrong.

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