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Thread: Ordering 1 freeform lens

  1. #1
    Master OptiBoarder TLG's Avatar
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    Ordering 1 freeform lens

    I need to order one Supercede lens for a patient. Looks like the MRP and PRP are the same.
    My question: is prism thinning used on freeform generated lenses just as standard process? Do I measure the EQ as I would on any other PAL?

    Our optical is forced to eat the cost of this lens purchased elsewhere so I'm trying to "git 'er done" with one go. Thanks as always for any help.

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    Rochester Optical WFruit's Avatar
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    There is no prism thinning done on Seiko Free Form lenses.

    That said, if at all possible it is always best to send in the complete Rx (both eyes) to the lab so they have a reference for the other eye.
    There are rules. Knowing those are easy. There are exceptions to the rules. Knowing those are easy. Knowing when to use them is slightly less easy. There are exceptions to the exceptions. Knowing those is a little more tricky, and know when to use those is even more so. Our industry is FULL of all of the above.

  3. #3
    One eye sees, the other feels OptiBoard Silver Supporter
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    Quote Originally Posted by TLG View Post
    I need to order one Supercede lens for a patient. Looks like the MRP and PRP are the same.
    My question: is prism thinning used on freeform generated lenses just as standard process?
    Good question. I assume it's used as needed, when there is sufficient plus power on the vertical meridian (including the Add power).

    Do I measure the EQ as I would on any other PAL?
    Yes.

    I've always considered the MRP and PRP to be interchangable terms. I believe that Seiko PALs have a zero drop, i.e the fitting reference point (fitting cross) resides on the 180 line. If the vertical OC position of the other lens is aligned with the PRP, and there is no prescribed prism, you should request zero prism thinning.
    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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    Master OptiBoarder TLG's Avatar
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    Quote Originally Posted by Robert Martellaro View Post
    I've always considered the MRP and PRP to be interchangable terms.
    I consider the MRP to be the reference point we measure (pupil center or whatever) for height, the PRP where we measure prism. In a 2 or 4 drop lens, they would not be the same; however in this case they would.


    Quote Originally Posted by Robert Martellaro View Post
    I believe that Seiko PALs have a zero drop
    Thanks, that's actually the term I was looking for, just couldn't pull the words out (but I did manage to work into this post; see, I'm coachable!).

  5. #5
    Allen Weatherby
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    Prism Thinning is possible

    I believe that Prism Thinning is possible but it depends on the software management system if there is a way to call for it.

    Yes the PRP and the fitting point are in the same location.

  6. #6
    Objection! OptiBoard Gold Supporter shanbaum's Avatar
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    Quote Originally Posted by AWTECH View Post
    I believe that Prism Thinning is possible but it depends on the software management system if there is a way to call for it.

    Yes the PRP and the fitting point are in the same location.
    That's an unfortunate way to state that, because it's unclear if you're saying that the PRP is definitionally the same as the "fitting point", or that on the Supercede, the two are coincident. The former statement is incorrect; the latter, correct.

    This thread serves to illustrate why the term "MRP" should be abandoned; there has never been sufficiently broad agreement on its meaning.

    Several Vision Council standards use the term "Prism Reference Point" ("PRP") to refer to that point on a lens at which the specified prism should be obtained. The term "Layout Reference Point" ("LRP") refers to that point on a lens at which the principal fitting specification shoud be obtained. That varies by class of lens: for a single vision lens, it is the Prism Reference Point; for a segmented multifocal, it's the segment; for a progressive lens, it's the fitting cross.

    On a progressive, the LRP may be coincident with the PRP, but usually isn't (the LRP normally being located 2-4mm above the PRP). On the Supercede (I wonder if they misspelled that intentionally?), I think that you're right, Alan, the two are coincident.

    I'm also reasonably certain that prism thinning is optionally calculated by the Epson lens design software (that's the way I would recommend it be configured), and that alternatively, the lens design software will incorporate prism thinning specified to it by the lab management software to which it may be, and usually is, connected.

  7. #7
    Allen Weatherby
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    Epson clairification

    Shanbaum, as usually clairifies the point in detail. For everyones information his mention of Epson refers to the actual technology provider for Seiko Optical Products.

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