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Thread: Progressive Prism balancing in Anisometropes

  1. #1
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    Progressive Prism balancing in Anisometropes

    Hi All,

    How should i fit a progressive in a anisometrope who has a such a RX:

    R) +2.00
    L) -2.00
    Add +2.00

    The amount of prism will be different in both eyes for definite. I have been always advised that the lab recommends doing the same prism along the PRP.

    Does anyone have a good idea of how to fit such Px and still get a high success in progressives? I sometimes adjust the lens nearer to the eyes for closer image size in BE.

    I think the progressive designs will be different too in a + lens as compared to a - progressive design. In this case, should freeform lens work better?

    Please give me some pointers :>

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    I would grind no prism in the prp. Is a slab off required?

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    Slab off

    Hi!!

    thanks for your reply.

    What is a slab off? do you mean those slabs that appear in Lenticulars?


    Please pardon me . Oops.

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    Look Up.......

    .....Bi-Centric Grinding/Slab-off and you will se it is designed to correct the significant imbalace at the reading level. The imbalance in this Rx in the 90th meridian, assuming a 10 mm reading level, is 4^. In the past, this was done on glass flat-tops and required a great deal of hand-crafting. Today it is available on progressive lenses via molding, and becoming more common in the US.

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    ATO Member HarryChiling's Avatar
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    Just a thought, and I don't know if it is even a good idea to do but in a flat top you can use two different segment designs to try to eliminate the prism imbalance. What about useing two different progressive designns with varying coridor lengths and powers to accomplish the elimination of the prism imbalance. Has anyone thought of it and if so is it feasable?
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    I believe this is called antimestropia{oppisite signs/anismetropia is a difference in powers but the same sighn} Please do not take this as nit picking but just wanted to clarify.

    In my experiance the first thing I would look at is; what is the patient wearing now as far as rx and a bifocal.

    In other words is this rx similar to what they are currently wearing or is it a signifacant change? Are they currently wearing a bifocal and if yes is it aprogressive?If they have a similar situation and are not having double vision you can prescribe without slab-off.

    I have fit patients with progressives with slab-off if they complain of double vision at the near{more so with implant patients with a one lens change in a current progreissive wearer}you can try it without slabb-off and see if the patient experiances diplopia/or just order it right at the git go/it all depends on you and your relationship with the patient if they want to aproach it what way as far as evaluating the rx and lens type.

    If slab-off is needed order it as REVERSE-SLAB-OFF/your lab can advise as this is becoming the way to aproch grinding slab-off

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    Enquiry

    TPL quote (I believe this is called antimestropia{oppisite signs/anismetropia is a difference in powers but the same sighn} Please do not take this as nit picking but just wanted to clarify.)

    Thanks! Learnt something new ;)

    Sadly, i have enquired with the labs and none of them know what is the slab off for progressive. The problem here is that, if the job is too difficult to do, not many labs will want to accept the job. They are very commercialised.

    Can you kindly give me some site that provide good write up for slab off for progressives?

    Btw, i did a pair of progressives for a antimesotrope some months back.

    1st pair,

    did the same amount of prism along PRP
    Adjusted the vertex distance as near as possible to reduce image size

    Px cannot adapt. Finds distance ok, near is terrible.

    Redo a 2nd pair,

    Adjusted the prism to be closer on the near progression zone (As compared to the 1st pair)
    Now prism are different in PRP and more different in Distant zone than in 1st pair.
    Px cannot adapt too.

    I used Seiko Back Surface progression lens (Normal Corridor design) for both orders.

    Sorry, when you say slab off, it will show as a slab in the progressive lens?? Wouldn't that be quite ugly? Sorry for asking but i have never seen such a lens yet.

    Thank you

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    OptiBoard Professional Ory's Avatar
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    The correct term is antimetropia/antimetrope.

    A slab off lens has a horizontal line across it. It is not typically too noticable but may be intolerable for someone who wants progressives due to vanity rather than visual reasons. Apparently some freeform lenses can incorporate the slab off without a noticable line.

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    If slab-off is needed order it as REVERSE-SLAB-OFF/your lab can advise as this is becoming the way to aproch grinding slab-off[/QUOTE]

    The slab is always done on the concave surface of a pal. Reverse slabs are molded on the convex surface of flat tops and must be surfaced on pals.

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    Anisometropia....

    ......is a term that refers to any difference in refractive power between the two eyes. It is only significant at 2 diopters or more. It is called antimetropia when one eye is myopic and the other hyperopic, but is still a form of anisometropia.

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    Master OptiBoarder ziggy's Avatar
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    I would first try to make them with out adding any prism. just order the Rx as you normally would. Most of the time, we can adapt to 2.5 D of imbalance.
    Paul:cheers:

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    Slab-Off Specialists

    You might try 'SLABS Plus'-

    They are Slab-Off specialists with address:
    319 First ST NE
    Ruskin, Florida 33570
    (813) 649-0225
    (800) 237-8501
    FAX:(800)552-0957

    They slab down to 0.5^ in glass, plastic, Hi-index, Poly with three (3) day turnaround and used to offer 50% off on first order.:cheers:

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    2.5^ VI imbalance is adaptable most of the time?

    I would first try to make them with out adding any prism. just order the Rx as you normally would. Most of the time, we can adapt to 2.5 D of imbalance.

    On what facts do you make such a statement?

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    slab of or reverse slab

    Hello,

    The Rx has 4.00^ of vertical imbalance at near. It is highly unlikely that the patient's brain will be able to fuse a single binocular image. If the patient doesn't get slab off or reverse slab, they will either suppress vision in one eye, alternately suppress vision, have asthenopia (tired, uncomfortable vison), and maybe even diplopia.

    The text book criteria is 1.50^ or more.

    : )

    Laurie

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    How much VI can be tolerated at near?

    ZIGGY says: "I would first try to make them with out adding any prism. just order the Rx as you normally would. Most of the time, we can adapt to 2.5 D of imbalance."

    Where do people come up with these numbers?

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    OptiBoard Novice foreyesemg's Avatar
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    No slab...Try this

    I learned something in CE's about 2 years ago. I have done this several times and it has worked even on patients that were already wearing slab off. Reverse the base curves used. ie...If you use a 4 base on the +2.00 and a 6 base on the -2.00, or even a 3 base on the +2.00 and a 7 base on the -2.00. Like I said I have had success with this at least half a dozen times in the past year or so. Not sure exactly why it works but I am sure someone out there would know. Good Luck

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    Quote Originally Posted by foreyesemg View Post
    I learned something in CE's about 2 years ago. I have done this several times and it has worked even on patients that were already wearing slab off. Reverse the base curves used. ie...If you use a 4 base on the +2.00 and a 6 base on the -2.00, or even a 3 base on the +2.00 and a 7 base on the -2.00. Like I said I have had success with this at least half a dozen times in the past year or so. Not sure exactly why it works but I am sure someone out there would know. Good Luck
    Your 'reversing' the base curves would result in a shifting of the two (2) len's primary and secondary principal planes, such that the respective difference in size of their images would be less apparent, thereby reducing the aniseikonia. But the quality of both len's imaging would become compromised due to the 'irregular' base curve selections.

    However, there would still remain substantial vertical prismatic imbalance (VI) at reading distance for near, so slaboff would still be required in this antimetropia Rx.

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    Biggest problem here , a bunch of ignorant advice.
    Lots of problems here . There are nO reverse slabs on progressives. Slabs themselves are stupid on progressives. You can only match the prism in one spot. Most patients needing slabs read with one eye. This because most opticians miss the fact that they may need a slab. If I were despinsing a progressive of this RX, I'd try with out the slab and let the patient read with one eye. Not explaining this to the patient. (call it a diservice if you will, but you ever heard of monofit?) If the patient later complained, I'd then explain the problem in detail and suggest a st!

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    Quote Originally Posted by Jim Mush View Post
    Biggest problem here , a bunch of ignorant advice.
    Lots of problems here .
    Mush should specify exactly what specific post's advice is 'ignorant', and then back it up with facts.:finger:
    Slabs Plus, the 'Slab-Off Specialists' specifically advertises the availability of slab-off on progressives. I personally do not recommend slab-off on progressives for cosmetic reasons. But so what if the VI is balanced at one spot only, that is the case with using ST's as well.
    There is no need to order reverse slab-off at all. Most full service labs can do the old BU regular slab-off.

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    Quote Originally Posted by tmorse View Post
    Mush should specify exactly what specific post's advice is 'ignorant', and then back it up with facts.:finger:
    Slabs Plus, the 'Slab-Off Specialists' specifically advertises the availability of slab-off on progressives. I personally do not recommend slab-off on progressives for cosmetic reasons. But so what if the VI is balanced at one spot only, that is the case with using ST's as well.
    There is no need to order reverse slab-off at all. Most full service labs can do the old BU regular slab-off.
    Pretty freaking to try to equalize the imbalance in progressives. It might have been yours. Somebody accused me of not wanting to slab a progressive for cosmetic reasons. Crap! I consider optics first always. Did I hit a sore spot there tm!?? Sounds like it WAS you! Fix it at only one spot and you may as well have a flat top.

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    MUSH Brain?

    Quote Originally Posted by Jim Mush View Post
    Pretty freaking to try to equalize the imbalance in progressives. It might have been yours. Somebody accused me of not wanting to slab a progressive for cosmetic reasons. Crap! I consider optics first always. Did I hit a sore spot there tm!?? Sounds like it WAS you! Fix it at only one spot and you may as well have a flat top.
    Looks like MUSH mouth needs therapy.

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    Quote Originally Posted by tmorse View Post
    Looks like MUSH mouth needs therapy.
    OK then there Tmo! I'll go get me some therapy. You go get some optical education!

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    My we are getting ugly boys. Just because you see things differently, no need to get nasty.

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    tmorse actually provides the education......he is known as the "optical encyclopedia". A very acurate label. I have seen him in "action".

    Quote Originally Posted by Jim Mush View Post
    OK then there Tmo! I'll go get me some therapy. You go get some optical education!

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    Quote Originally Posted by mullo View Post
    tmorse actually provides the education......he is known as the "optical encyclopedia". A very acurate label. I have seen him in "action".
    LOL.LOL.LOL.LOL Butt kisser!:D Just don't let tmo talk you in to slabing a progressive. It really is a dumb and waistful thing to do.
    Last edited by Jim Mush; 10-16-2006 at 08:46 PM.

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