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Thread: Miopia Control

  1. #1
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    Confused Miopia Control

    Anyone familiar with miopia control; specifically, adding base in prism to the near portion only in executive bifocals? How does that work (are the adjustments made during surfacing, finishing, both, etc.)?

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    OptiWizard
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    You might mean Franklin bifocals. Myopia control is a popular topic in the trade magazines. Not sure I subscribe to it. Optiboard has Optometrists swimming around - they could address this more competently than I can. I always treated it like a mechanical issue rather than a disease. Some of the modern control methods make me wonder.

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    If you want base in near only, use the segment power and Prentice's rule to determine additional inset needed to produce the desired prism. This usually requires the widest available seg ST35/40/45, whatever is the widest you can get is. If the patients PD is 64/60, they have a 2.50 add, and they need 1BI near only each eye, the segment will need to be decentered an additional 4mm per eye. So the lenses will be made with the near PD at 26 for each eye.

    You could certainly do it with a Franklin as suggested and would need to if the prism amount is high or the add power is low. I don't think you can do it with an executive?

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    Dec entering a +2.50 add 4 mm will only give you the desired result if the distance is Plano. The power in the reading portion is the combination of the distance Rx and the reading power in addition the o.c. In the the near is never in the middle of the seg except if the distance is Plano. The only way to do this is Franklin stay made of two independent s.v. Lenses.

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    Master OptiBoarder optical24/7's Avatar
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    Lensman, you’re looking at this as I did, and we were both wrong. Kwill is correct. Go to this post, start at #61 and keep reading. When you put your surfacing hat on it all makes sense.

    https://www.optiboard.com/forums/sho...ter-Exam/page3

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    I will tell that thread you mention is incorrect. The seg is not an independent lens unless their is no power in the distance. If you take an exec lens with a minus correction in the distance and grind prism for decentration the distance oc will go in as expected and the oc thru the seg will go out. So when you put two lenses on top of each other the result is the combination of both powers.
    check any pair of bifocals where the distance Rx is stronger than the seg power and you will see the the near oc is not where you expect it to be. Realty is that no one checks near pds by dotting the seg they do it by checking seg location with a mm ruler.

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    Quote Originally Posted by Lensman11 View Post
    I will tell that thread you mention is incorrect. The seg is not an independent lens unless their is no power in the distance. If you take an exec lens with a minus correction in the distance and grind prism for decentration the distance oc will go in as expected and the oc thru the seg will go out. So when you put two lenses on top of each other the result is the combination of both powers.
    check any pair of bifocals where the distance Rx is stronger than the seg power and you will see the the near oc is not where you expect it to be. Realty is that no one checks near pds by dotting the seg they do it by checking seg location with a mm ruler.

    It's not. Here is another thread explaining it. https://www.optiboard.com/forums/sho...g-decentration


    Now if you want to say that thread is wrong as well, go ahead. Try System for Ophthalmic Dispensing 3rd edition, starting on page 445. "Creating horizontal prism at near only" and you will see that this thread, and the other two threads are correct. This is how it is done by the book, and this is how every lab that surfaces these jobs does it , correctly. Maybe it's time to put your slide rule away and crack a book.

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    Master OptiBoarder OptiBoard Silver Supporter
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    If that's not enough you can refer to Understanding Lens Surfacing by Clifford Brooks chapter 16. Yes there in entire chapter called "Creating horizontal prism with the near addition". Most of it is summarized in Systems for oph. disp. but this has more details.

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    Just put lenses in a lensometer and see what happens. What you saying will come close to working if the add is stronger than the distance. If you are correct than every seg oc will be centered and five below the top of the seg. Measure some and see what you get.

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    Master OptiBoarder OptiBoard Silver Supporter
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    Does not know answer when told, got it. I'm out.

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    All that aside, there is little support for base in prism and myopia control. Atropine, multifocal soft contact lenses and orthoK are the options that have some research support.

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    Quote Originally Posted by Michael Davis View Post
    All that aside, there is little support for base in prism and myopia control. Atropine, multifocal soft contact lenses and orthoK are the options that have some research support.
    Yes.

    Also there is some rumors on Single vision lenses with add like essilor eyezen and similar but nothing is sure.

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    Master OptiBoarder optical24/7's Avatar
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    Another way to visualize it, why do we grind decentration on bifocals? To eliminate unwanted horizontal prism at near as the eyes converge. What would happen if I grind a lens with no decentration, then edge the lens to the Distance PD? There would be no prism at distance, but my segs were now base out compared to where the near PD should be.

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    The reason you grind decentration in a bifocal is as you stated but you can’t control where the oc ends up in the seg. You are grinding decentration to position the seg so near gaze will be centered in the seg and the distance pd will be correct. If you have an Rx- 2.00 in the distance with a +2.00 add what horizontal prism are you eliminating.

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    Master OptiBoarder optical24/7's Avatar
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    Go to post 116, I explain how this works on a -2.00 dist, +2.00 add.
    https://www.optiboard.com/forums/sho...ter-Exam/page5

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    I had to read your post several times so as I understand it you are creating a Plano prism thru the seg. Makes sense but initially my thoughts went in a different direction.

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    Now that I jumped down the rabbit hole. You are creating two base in prism by moving the seg 5 mm but depending on the distance Rx it would be a combination of the prism created by the power and distance from the seg of the distance Rx. So if the Rx called for two base in at near only this would not be filling that requirement. Any one checking this Rx would want to find two base in at the near pd.

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