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Thread: How to offset unwanted prism

  1. #1
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    How to offset unwanted prism

    Our lab called to tell us that a patient's frame pd is too large for the patient's pd. The patient is adamant about staying in his choice of frame. He wants progressives and his prescription is the following:

    OD -3.00 -1.00 x 068
    OS -3.75 -0.50 x 115
    +2.25 add

    Distance pd = 31.5/31.5
    Frame Eye Size = 60
    Frame DBL = 18

    The minimum pd required for the frame is 34.5/34.5.

    I am not confident about my calculations, but could someone double check me? I think that the amount of unwanted prism would be 1.2 BO in each eye, totalling 2.4 BO. In order to offset this, I was going to ask the lab to grind 1.0 diopters of prism in each eye. I am just confused if it should be BO or BI. Help! Do you think this will alleviate any potential double vision problems the patient might encounter by such a large decentration?

  2. #2
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    I would talk to your lab and ask them what you could do and if you put the pt pd at 34.5 witch is the minimum on that frame the pt eyes would inword of that so that would make the prism BI so I wood think you would want base out . Not sure if you can do somthing like this with a pal.

  3. #3
    ABOM Wes's Avatar
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    Unfortunately, grinding prism on the back of a pal to offset the prism you're considering creating by changing the decentration by 3 mm OU will not help. If this were a SV lens, you'd be on the money with the idea, but since the intermediate corridor and add are on the front of the PAL, they would unusable.

    Do you have PAL cut out charts? depending on the seg ht, the following may vary a bit:
    to determine the minimum blank size, you take the ED of the frame, add the dbl and total that. It should be at least 78+ mm. Half this # and take the difference between it and the pts mono pds of 31.5, double that and add that number to the frame pd (plus 2mm for good measure) and you have: 39+mm -31.5 = 7.5+ mm X 2 = 15+ mm + 60 mm (+2) = 77+mm minimum blank size.
    You need to talk to your lab, find out what the largest blank size for their various pals are. Maybe you can find one that works. Maybe you can't. Armed with this info, you can talk to the pt about using a smaller frame.
    Wesley S. Scott, MBA, MIS, ABOM, NCLE-AC, LDO - SC & GA

    “As our circle of knowledge expands, so does the circumference of darkness surrounding it.” -Albert Einstein

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    You only hope is for a larger progressive or if a decentered progressive of another manufacturer may help. You can't grind enough prism to move that PD of ther semi finished progressive. That or a freeform should be placed where it needs to be. Did your lab suggest any alternative than changing the frame? Does your lab have freeform capabilities? Questions you shopuld have answers for.

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    retro problem.................

    The cut-out charts are critical, and should help you decide which progressive brand to use. Lens manufacturers need to catch up to the demand for larger frame sizes, and full blank service.

  6. #6
    Master OptiBoarder OptiBoard Gold Supporter Judy Canty's Avatar
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    AND...sometimes the patient is just wrong.

  7. #7
    Master OptiBoarder optical24/7's Avatar
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    Two designs I can think of, Auto II and iCoat's Inscribe FF lenses, offer variable inset/decentered designs (ground off geo center to give you a larger effective blank size). The only limitation (for the most part) is blank thickness to start with.

  8. #8
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    Quote Originally Posted by CuriousCat View Post
    AND...sometimes the patient is just wrong.
    1+

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    Master OptiBoarder Darryl Meister's Avatar
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    Lens manufacturers need to catch up to the demand for larger frame sizes,
    I'd say that the real problem here is big, ugly eyeglass frames, not the small cut-out of a decentered, 75 mm lens blank. Some fashions from the 70s and 80s should never be allowed to come back in style, like leg warmers and parachute pants.


    Best regards,
    Darryl
    Darryl J. Meister, ABOM

  10. #10
    Master OptiBoarder
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    Yes, Darryl, and yet while I agree with you......................I am glad to see the "vertically challenged" frames of the Zeros in the rear view mirror, too!

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    No matter what you do yor going to create unwanted prism ..............only way is a different vari
    WHAT LENS HAVE YOU COME UP WITH ?????

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    lens-o-matic bhess25's Avatar
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    even with an 80mm blank size the effective blank size is still too small, ask your lab to use a different progressive lens. You have 9mm decentration in each eye (a horrible fit for sure, but im not blaming you), thats big. The only lens that I know of that would work is the image wrap, however it only comes in polorized. Maybe the nice folks at younger will one day make one decentered the same as the image wrap in clear so we can do things like gradient tints and other options consumers ask for. i know there is another progressive that is decentered 4mm in the blank, i just cant remember what lens it is.
    equal opportunity offender!!

  13. #13
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    Its real simple. DECENTERED SOLA VIP BLANKS WILL WORK. YOUR WELCOME.

  14. #14
    Doh! braheem24's Avatar
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    They be made?

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    Doh! braheem24's Avatar
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    Add some faceform and use an image wrap.

    http://www.optiboard.com/forums/show...entered-Design

  16. #16
    lens-o-matic bhess25's Avatar
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    Quote Originally Posted by braheem24 View Post
    Add some faceform and use an image wrap.

    http://www.optiboard.com/forums/show...entered-Design
    what if he doesnt want polorized?
    equal opportunity offender!!

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    Master OptiBoarder optical24/7's Avatar
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    Why would you use an old decentered design instead of a FF with POW optimization?

  18. #18
    Doh! braheem24's Avatar
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    Quote Originally Posted by bhess25 View Post
    what if he doesnt want polorized?
    He don't wanna wear his sunglasses at night?

    Sorry, didn't know they only came in polar.

  19. #19
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    Polarized, not polorized.

  20. #20
    Doh! braheem24's Avatar
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    Since you bring it up, Do a search for the word "concider" on optiboard.

    I'm assuming it means consider.

  21. #21
    lens-o-matic bhess25's Avatar
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    Quote Originally Posted by chip anderson View Post
    Polarized, not polorized.

    thanks for your wealth of optical knowlage....i dont freakin care how its spelled it got the point accros!!...stop ripping on everyone and share some of that 200 years of optics you have under your belt and at least try to "act" like you know how to be helpful.
    equal opportunity offender!!

  22. #22
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    In this case.... restyle. The customer is not always right!

  23. #23
    Master OptiBoarder OptiBoard Gold Supporter DragonLensmanWV's Avatar
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    I believe the Sola VIP Decentered blanks are only in 5 base.
    DragonlensmanWV N.A.O.L.
    "There is nothing patriotic about hating your government or pretending you can hate your government but love your country."

  24. #24
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    Quote Originally Posted by chip anderson View Post
    Polarized, not polorized.
    Something you must watch out for with most polarized progressives when there cut out is tight is the markings that indicate the 180. A 'clear, unploarized' notch that often decreases the usable size. I never figured why the manufacturers feel the need for this on progressives.

  25. #25
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    These types of jobs are a cinch for Ice-Tech. They have done some truly amazing stuff for us! I've done polar. PAL's in a 64 eye with a pat. PD of 60 using Ice-Tech's lenses.
    Clinton Tower

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