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Thread: In distress over a Prism Job

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    Confused In distress over a Prism Job

    Good morning all! Its been a while since I have been on here. I hope all ringed in the new year with a bang.

    I am hoping to get some advise.
    To start off the question is:
    Will using a larger lens than what a patient has been in before cause a patient with prisms to suddenly see what she describes as "bars of color" above and below the letters on the Snellen chart? The patient has gone from a very tiny "kids frame" sized frame to a bit larger "geeky" wayfarer type plastic frame.

    She is new to our office (coming from an optometry/chain store). She has VSP and high + power and cylinder, plus prisms and her eyes don't have a reliable PD. She doesn't have Nystagmus but they go back and forth regarding which one dominates, shifting. She is in and has been in progressives before. We have redone her lenses 2x already and she continues to complain of seeing a shadow of color around things that she doesn't in her old glasses and doesn't see while wearing a trial frame with the new Rx.

    At this point I am 1. embarrassed we haven't been able to get it right and 2. feeling bad that she still hasn't been able to walk away with her new glasses. The worst part is that she was so happy with the service she received starting from the doctor and especially with the service at the optical in regards to the help she received choosing a frame etc. She has been patient during this whole ordeal understanding that her Rx isn't typical and her eyes are uncooperative but I am starting to think I need to refer her back to her previous dispenser because I need to get her into her new glasses one way or another; whether I do it or not.

    Not sure if my question can even be answered but any advise at this point would be well received.

  2. #2
    Doh! braheem24's Avatar
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    remake in trivex and use an oc

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    OptiBoard Apprentice kemmer59's Avatar
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    You could call the office to get details on the glasses she purchased there. I have called on a few over the years to narrow down a problem.

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    Larger lenses can increase thickness which could cause chromatic aberration (color separation). The high plus RX can also be causing spherical aberration away from the the OC. I have had this happen also to a pt that wanted to switch into a more fashionable frame, didn't work. The wandering pd will just cause more susceptibility to experience these higher order aberrations (HOA's). I think you best bet at this point is to restyle into a small more round shaped from. They type she was probably in before.

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    It was made in the exact same progressive shes been in and high index. I have reached out to the other lab but either they are too busy to deal with it or don't want to give me the info. Erichwmack you are correct, she is in a smaller rounder/albeit ovalish shaped frame. I was thinking the same thing regarding the aberrations. Have you ever had a patient wear the lenses for a week to see if they adapt?

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    Quote Originally Posted by erichwmack View Post
    Larger lenses can increase thickness which could cause chromatic aberration (color separation). The high plus RX can also be causing spherical aberration away from the the OC. I have had this happen also to a pt that wanted to switch into a more fashionable frame, didn't work. The wandering pd will just cause more susceptibility to experience these higher order aberrations (HOA's). I think you best bet at this point is to restyle into a small more round shaped from. They type she was probably in before.
    Hi erichwmack,

    dv's color fringing problem is most likely due to chromatic aberration; increasing the material's Abbe value will reduce the color fringing and/or blur. However, reducing the thickness will have no effect on CA. SA is also not a concern due to our small pupils.

    dv,

    occlude the fellow eye when you measure the IPD.
    Last edited by Robert Martellaro; 02-03-2015 at 11:43 AM.
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    Hi Robert,

    I agree with you but the spherical aberration I feel is a real problem here. Pehaps the color fringing could be due to the high plus lens/prism deisgn acting like a spectrum prism depending on the oblique regions? Even with small pupils the aberration should still be considered. A high plus lens is going to be subject to the HOA as the gaze is directed farther away from the optical axis. The wavefront will not be perfectly corrected towards the periphery. Pupil sizes will change according to conditions as well as position of wear.

    Eitherway, I have this happen to a pt in the past and

    I have had this problem in the past and it was definitely not fixed by adaption. Vertex distance and position of wear are important in these high power cases where you are trying to put into large "fashionable" frames. tricky business!

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    Really really sounds like 1.67 is the problem, IMHO. Remake in trivex or in 1.60 and make sure that you align the OCs.

    If you feel you can't reliably get the PDs from a CRP, get them from the old pair!!

    She sees fine with the RX in the Crown Glass lenses of the trial frame, so try to get as close ABBE value of material to that as possible!

  9. #9
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    Quote Originally Posted by erichwmack View Post
    Hi Robert,

    I agree with you but the spherical aberration I feel is a real problem here. Pehaps the color fringing could be due to the high plus lens/prism deisgn acting like a spectrum prism depending on the oblique regions? Even with small pupils the aberration should still be considered. A high plus lens is going to be subject to the HOA as the gaze is directed farther away from the optical axis. The wavefront will not be perfectly corrected towards the periphery. Pupil sizes will change according to conditions as well as position of wear.
    What you are describing is Lateral Chromatic Aberration.

    We can calculate lateral chromatic aberration (LCA) by dividing the prism (P) produced at a given point through the lens using Prentice's rule, by the Abbe value (v) of the lens material.

    LCA = P/v

    Values for P includes prescribed and/or induced prism.

    For example, Rx is plano sphere OU with 10 prism diopters base out total. If we do not split the prism, and use a 1.67 refractive index material with an Abbe value of 32, the LCA is .31^, and if split, .16^. Using Trivex with an Abbe value of 44, the LCA is .23^ and .11 respectively.

    Effect of chromatic dispersion of a lens on visual acuity.
    -Meslin D, Obrecht G.

    http://www.ncbi.nlm.nih.gov/pubmed/3348347

    LCA VA
    .05^ 20/21
    .10^ 20/22
    .15^ 20/24
    .20^ 20/26
    .25^ 20/28
    .30^ 20/31
    .35^ 20/34
    .40^ 20/39
    .45^ 20/44
    .50^ 20/51

    HOA's are really not a concern when designing ophthalmic lenses, except for PALs, where coma and trefoil can be managed somewhat, but not eliminated.

    Vertex distance and position of wear are important in these high power cases where you are trying to put into large "fashionable" frames. tricky business!
    Reducing the vertex distance is the only other way to reduce LCA; it reduces ocular rotation need to keep the object in view, keeping the eccentric gaze closer to the OC. The exception is with prescribed prism (note the example above), where LCA can be very high even with the primary gaze.
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    Master OptiBoarder MakeOptics's Avatar
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    I don't have a magic bullet but I can offer a few suggestions:


    1. Seeing color fringes means TCA Trans Chromatic Aberration. This has everything to do with the material. Keep the abbe high, CR, Trivex, 1.6 are the go to's for this script.
    2. Going off axis is not your friend, small frame to a larger frame is a bad idea. You don't want her looking towards the edges of the lens since the prism ramps up as you move away from the optical center so the smaller the lens the less likely she is to get outside of the boundary that does not exist.
    3. Short corridor progressive, for the same reason above the further she looks down the corridor the higher the prism gets and the more likely light breaks up into it's color components.
    4. Fit vertex close, any material even glass is going to cause some fringing, the closer it is to the eye the less distance the rays have to separate take advantage of that and fit the lenses close.
    5. Prism thinning, make sure that whatever her primary goal is for the pair you fit so the prism in primary gaze has the least amount of prism tolerable at that point, what that means is you may have to order the lenses with no prism thinning or even with yolked prism in the opposite direction so that the primary gaze has just the prescribed prism to avoid any additional fringing.
    6. Tint, a slight tint to reduce the contrast will help sometimes if the patient is ok with filtering out one side of the fringe. Slight amber will filter the blue fringe but allow the red fringes to come through (I have found the blue edge to be more problematic), a slight blue will filter out the red end of the fringes and allow the blue fringe to come through (not as effective, IMO) or a yellow to allow the middle of the spectrum (most sensitive during photopic vision) to shine through while reducing the red and blue.
    7. AR, AR in and of itself will not correct the situation but many of the new blue blocking AR's will reflect the blue end of the spectrum reducing the blue fringe.
    8. Discuss two pair as an alternative to a one size fits all solution to avoid placing compromise in one gaze or another.
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    Master OptiBoarder MakeOptics's Avatar
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    Robert great minds think alike, LCA is not as problematic as TCA. Very much the same effect but accommodation can help with LCA whereas TCA results in blur that cannot be accommodated for (simple explanation).

    Correction, I assumed you meant LCA was longitudinal chromatic aberration not LATERAL which is Transverse. Next time I'll read your source first.
    Last edited by MakeOptics; 02-03-2015 at 01:55 PM.
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    Quote Originally Posted by MakeOptics View Post
    Robert great minds think alike, LCA is not as problematic as TCA. Very much the same effect but accommodation can help with LCA whereas TCA results in blur that cannot be accommodated for (simple explanation).

    Correction, I assumed you meant LCA was longitudinal chromatic aberration not LATERAL which is Transverse. Next time I'll read your source first.
    They have the same acronym!

    I've read that longitudinal or axial chromatic aberration in ophthalmic lenses is possibly masked by our eyes own Longitudinal/Axial chromatic aberration, and that's why we don't notice it. But I wonder if it doesn't interact in some way with other aberrations to cause that very rare complaint of color when looking in the primary gaze with low levels of prism, when wearing PALs.
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    I cant tell you how exciting it is for me to read your replies!! Daunting to a point and totally over my head at times unfortunately but exhilarating :) Yes I am a nerd.

    Anyway, her old glasses (which she doesnt have a problem with)

    1.74 Physio Enhanced with Crizal. Old Frame is Metal A: 45 ED: 47

    The current Frame is ZYL A: 45 ED: 45.9 same exact PAL and AR

    Rx: OD: +5.25 -3.25 x 115 with 5.0 BO
    OS: +5.00 -3.00 x 071 with 3.5 BO and 1.0 BD
    Add: +2.00
    Not sure if this makes things a bit clearer.

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    Master OptiBoarder OptiBoard Silver Supporter Jubilee's Avatar
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    I am confused. If the frame is larger, how is the ED smaller?
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    What is the current frame wrap in degrees? Did you use compensated POW? Did the old ones use compensated POW? IE: were they Physio enhanced Fit? (I would have used that same lens for this patient BTW)

    What are the old/new PDs. What is the vertex distance of the frames on her?

    At this point you have to get into the nitty gritty of the variables to find anything/everything that is different.

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    dv,

    check for changes in the prescribed prism. Check the thinning (yoked) prism also.

    Robert

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    Master OptiBoarder optical24/7's Avatar
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    Quote Originally Posted by dv View Post
    I cant tell you how exciting it is for me to read your replies!! Daunting to a point and totally over my head at times unfortunately but exhilarating :) Yes I am a nerd.

    Anyway, her old glasses (which she doesnt have a problem with)

    1.74 Physio Enhanced with Crizal. Old Frame is Metal A: 45 ED: 47

    The current Frame is ZYL A: 45 ED: 45.9 same exact PAL and AR

    Rx: OD: +5.25 -3.25 x 115 with 5.0 BO
    OS: +5.00 -3.00 x 071 with 3.5 BO and 1.0 BD
    Add: +2.00
    Not sure if this makes things a bit clearer.
    Check to see if the prism was split last time or this time. Also check to see if the PD was comped for the prism this time or last. ( .30 mm per D towards the apex.) Check the exact prism amount of each pair at the PRP.

    Robert, MO, ( others ) I'm wondering if the prism distribution between the two could put this patient's pupil at a different position ( edge of the umbilic ) causing some kind of birefringence?

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    Quote Originally Posted by Jubilee View Post
    I am confused. If the frame is larger, how is the ED smaller?
    The chunky zyl probably looked a lot larger than the old metal. I know I've been fooled before. But I understand your frustration- hard to troubleshoot without good data!

    Quote Originally Posted by optical24/7 View Post
    Check to see if the prism was split last time or this time. Also check to see if the PD was comped for the prism this time or last. ( .30 mm per D towards the apex.) Check the exact prism amount of each pair at the PRP.

    Robert, MO, ( others ) I'm wondering if the prism distribution between the two could put this patient's pupil at a different position ( edge of the umbilic ) causing some kind of birefringence?
    Not much power on the horizontal meridian, but worth checking, more for alignment issues IMO.

    Nice idea on how the prism might have been distributed, especially when we consider how it was written! We need more hard data.

    WRT birefringence, I never associated that with visual symptoms, instead more of a cosmetic concern, and then only under certain types of light, or through a polarizing filter.


    dv,

    this cut and paste from Brook's Optical Dispensing News that I subscribed to about 15 years ago adds to optical24/7's explanation about adjusting the fitting cross on PALs with prescribed prism.

    From Clifford W. Brooks, OD Indiana University School of Optometry Bloomington, IN

    In a recent Optical Dispensing News, Rajesh Wadhwa brought up the problems encountered when prescribed prism is used with progressive addition lenses. Many people with prescribed prism have problems with their progressive lenses because the monocular PDs and fitting cross-heights are measured in the empty spectacle frames without the prism in place. When the prescribed prism is added, the eyes do not "point" in the same direction as they did during lens fitting measurements.

    To avoid this problem, the person measuring for progressive lenses needs to anticipate the amount the eyes will be displaced by the prism. This amount is about 0.3 mm for every diopter of prescribed prism. The eye will turn in the direction of the prism apex -- away from the base direction.

    For example, let's take a patient with 5.00 D of prescribed base-in prism for each eye. The patient is measured for progressives using a pupilometer (or ruler) without this prism in place. Monocular PDs are found to be 30 mm for the left eye and 30.5 mm for the right eye. Because of the way the eyes will turn with the prism in place, the monocular PD measurements would need to be changed to 31.5 mm for the right eye and 32 mm for the right eye.

    The same compensation is used for fitting-cross height in the presence of prescribed vertical prism.
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    I learn so much here on optiboard. This displacement of the fitting point location makes sense when the progressive optics are on the front of the lens and the prism is ground on the back. Is this displacement as beneficial\ necessary if the whole lens is surfaced on one side as in the shamir spectrum(my go to prism pal BTW, probably not in the OP's doozy of an RX though). Or is the freeform design shifted with the prism direction during its calculation?

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    Master OptiBoarder optical24/7's Avatar
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    It would make no difference if the prism was applied on the convex or concave side. Prism displaces the pupil (as the eye views through it.) I know of no FF design that has this comp in their designs when prism is prescribed.

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    We had this discussion before.

    I had an issue with it before. I'll try to find it.

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    Quote Originally Posted by drk View Post
    We had this discussion before.

    I had an issue with it before. I'll try to find it.
    One issue for sure is that high levels of prescribed prism combined with compensated optics usually ends up in the Lions Club bin.

    My guess is that the OP's client had a bump in prism diopters, primarily in the good(?) eye, causing the bottom to fall out due to increased chroma and a breakdown of the optics. The thread is data-lite, so that's my stab in the dark, FWIW.
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    Quote Originally Posted by Robert Martellaro View Post
    They have the same acronym!

    I've read that longitudinal or axial chromatic aberration in ophthalmic lenses is possibly masked by our eyes own Longitudinal/Axial chromatic aberration, and that's why we don't notice it. But I wonder if it doesn't interact in some way with other aberrations to cause that very rare complaint of color when looking in the primary gaze with low levels of prism, when wearing PALs.
    LCA or TCA whichever way we refer to it is chromatic aberration, monochromatic aberrations are the other HOA's, we use one specific wavelength of light when computing monochromatic aberrations but the other wavelengths experience these same HOA's and sometimes in opposite directions exacerbating the problem. That's why material selection is the foundation of lens design and every great design starts with the right material FIRST. I gave a presentation on chromatic aberrations once where the entire room had glassed over eye's except 1 or 2 attendees, where we actually took my prescription (I didn't tell anyone this) and designed the perfect lens reducing aberrations. The end of the presentation I mentioned that the monochromatic aberrations also are effected by the material choice and have an associated chromatic error as well.

    The human eye does not necessarily mask the chromatic aberrations which is present in the system of lenses that comprise the eye. Our sensor the retina is responsible for this lack of resolution, 5-10 degrees is the area of primary gaze that is responsible for details such as reading text, 10-30 and the resolution drops to resolving shapes, 30-60 and we can resolve color, beyond 60 degrees we pretty much just make out motion. The retina is comprised of 91 million rods to 4.5 million cones, the fovea is only 1.2mm on average in diameter with roughly 200 times more cones than rods present with the foveola (central 300 micrometers containing zero rods). The high density of cones in the foveola is responsible for the lions share of our vision and cones are responsible for color vision, the further from the fovea we go the loss of cones and density of cones means our color vision is compromised in the peripheral retina. That loss in resolution saves us from the effects of chromatic aberrations of the eye and of lenses, however with lenses we can turn our eye through the peripheral sections of the lens exposing this dense section of our retina to the effects of the peripheral effects of the lens material. The eye's chromatic aberration stays constant as the lenses that comprise the eye travel at the same degree of rotation as the retina. I know you get it, but it's a great subject so I thought I would expand upon it for others on the thread to highlight the depth of your question and the beauty of the answer.
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