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Thread: Prism - Need some suggestions

  1. #1
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    Prism - Need some suggestions

    OD: -0.75 -0.50 x 150 3 BU 22.5 BI BCVA 20/20
    OS: -6.00 -1.50 x 150 3 BD 22.5 BI BCVA 20/40

    New patient without glasses and unable to get previous records. I haven't run up against a Rx like this before and could use some suggestions to provide the best compromises between lens/vision.

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    Eyes eastward... Uilleann's Avatar
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    Quote Originally Posted by jmainwar View Post
    OD: -0.75 -0.50 x 150 3 BU 22.5 BI BCVA 20/20
    OS: -6.00 -1.50 x 150 3 BD 22.5 BI BCVA 20/40

    New patient without glasses and unable to get previous records. I haven't run up against a Rx like this before and could use some suggestions to provide the best compromises between lens/vision.
    It can be ground, but that is going to be rather tricky with so much nasal thickness. The obvious advantage of ground is the better optics. The obvious disadvantage is nasal thickness and depending on frame, and pt's facial structure, could end up being un-wearable. Fresnel can work, and the thickness issue disappears. However, quality of vision is going to be pretty poor with those numbers,

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    OptiBoard Apprentice fagin's Avatar
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    Try a balance lens on the left, ditch the prism altogether and see if suppression gives a satisfactory outcome.

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    Doh! braheem24's Avatar
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    I Doubt the patient is fusing 6 diopter of anisekonia, I agree with dropping the prism also but I would keep the full rx, if that does not work then use a balance os.

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    OptiBoard Apprentice fagin's Avatar
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    I'd ditch the Rx too - keeping the VA lower in the left would keep any chance of visual confusion in the hunt for binocularity to a minimum, but its going to be trial and error all the way. Good luck !

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    A balance lens was discussed, but the doctor and patient wanted to make an attempt at using both eyes. This Rx is the result of a recent traumatic injury.

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    OptiBoard Apprentice fagin's Avatar
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    in that case, Fresnel the total resultant prism in the left eye and be very guarded about the likely outcome.

  8. #8
    Doh! braheem24's Avatar
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    +6.00 contact lens OD, then full rx.

    The -6.00 resultant Rx OD will help the anisekonia as well as the prism thickness nasally and/or combination of a 40D fresnell prism OS only.

  9. #9
    One eye sees, the other feels OptiBoard Silver Supporter
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    Quote Originally Posted by fagin View Post
    in that case, Fresnel the total resultant prism in the left eye and be very guarded about the likely outcome.
    I'll assume that this is an adult.

    I thought that the VA degrades quickly over 25^, approaching 20/100, and 20/200 over 30^. You might as well use a MIN occluder, or balance as you previously suggested, depending if suppression is significant enough to minimize diplopia.

    Quote Originally Posted by braheem24 View Post
    +6.00 contact lens OD, then full rx.

    The -6.00 resultant Rx OD will help the anisekonia as well as the prism thickness nasally and/or combination of a 40D fresnell prism OS only.
    I see, the goal is to get some minus on the right to balance the nasal thickness. I'm not sure if that will influence the appearance in any significant way with that much prism!

    Another possibility with CLs is to correct the left eye, use a 25^ Fresnel on the left, and surface 10^ in each eye, or just skip the CL if trial framing shows no disadvantage in doing so.
    Science is a way of trying not to fool yourself. - Richard P. Feynman

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    Compulsive Truthteller OptiBoard Gold Supporter Uncle Fester's Avatar
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    If ou prism applies does the pd need to be compensated for this much prism or is that only true if progressive?
    Last edited by Uncle Fester; 04-16-2013 at 10:54 AM. Reason: tweak...

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    One eye sees, the other feels OptiBoard Silver Supporter
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    Quote Originally Posted by Uncle Fester View Post
    If ou prism applies does the pd need to be compensated for this much prism or is that only true if progressive?
    That might be a case of what came first, the chicken or the egg! Seriously, we may have to compensate (the eye turning towards the apex .3mm per prism diopter) for any type of multifocal. For example, a significant amount of vertical prism would misalign the segments- too high on the eye with prescribed base up prism, and too low for the eye with the base down.
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    Compulsive Truthteller OptiBoard Gold Supporter Uncle Fester's Avatar
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    What about the horizontal prism?

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    If this is a lens prescription, I'm not sure how you can just "drop" part of the lens prescription because it is thought to be impractical to manufacture. I would recommend that Fresnels for horizontal and decentration or ground prism for the spectacle lenses. The Rx in the OS may be prescribed to prevent diplopia and not correcting it might cause the deviation to increase.

    A contact lens may help in image asymmetry but spectacles will be needed for the prism.

    Quote Originally Posted by jmainwar View Post
    OD: -0.75 -0.50 x 150 3 BU 22.5 BI BCVA 20/20
    OS: -6.00 -1.50 x 150 3 BD 22.5 BI BCVA 20/40

    New patient without glasses and unable to get previous records. I haven't run up against a Rx like this before and could use some suggestions to provide the best compromises between lens/vision.

  14. #14
    One eye sees, the other feels OptiBoard Silver Supporter
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    Quote Originally Posted by Uncle Fester View Post
    What about the horizontal prism?
    If there's enough dioptric power, one might redefine and chase the PRP, adjusting the prism to compensate, but I get a headache thinking about it.

    Quote Originally Posted by npdr View Post
    If this is a lens prescription, I'm not sure how you can just "drop" part of the lens prescription because it is thought to be impractical to manufacture
    Not impractical to manufacture, but possibly impractical to wear. I'd discuss it with the prescriber.
    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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    Oh my Robert- you're always catching me with my PD stick exposed

    PRP? Prism reference point???

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    Quote Originally Posted by Uncle Fester View Post
    Oh my Robert- you're always catching me with my PD stick exposed

    PRP? Prism reference point???
    Yes. PRP replaced MRP about 10 years ago because "Major Reference Point" was a tad vague. The PRP is the point where we measure for prescribed prism. If there is no prescribed prism, then it's the OC or optical center.

    Acronym hell.

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  17. #17
    What's up? drk's Avatar
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    You really do have to question the earnestness of the prescription. I'd call the prescriber, as well. Is this just "a try" (in which case you can forget it...it's not going to work) or is this a serious attempt?

    What are the alternative vision correcting options? Has a CL been tried? Is refractive surgery at all possible? Is muscle surgery for a 45^ exodeviation a possibility? Is this a permanent situation or transitory?

    It seems like maybe there was a retinal detachment in the left eye, and possibly a post-surgical exotropia? Or is it neurological? Is this patient pseudophakic? Is the patient suffering from diplopia? Has the patient demonstrated binocular fusion with 45^BI in the office? Can they fuse with gaze anywhere off the optical center, or is it head-turn city?

    If they want to go forward, I'd charge a whole lot for the initial design service, plus the cost of the supply of lens materials (the frame can be standard pricing), and charge professional fees for followups as needed and again materials costs for remakes.

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