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Thread: Neutralizing a progressive lens

  1. #1
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    Neutralizing a progressive lens

    I realize this has probably been done many times on this board, but I just joined and cant find it easily. I was trained as an optician 20+ years ago in the Navy. We didn't have PAL's then, so I never really learned to read them. After 12 years teaching high school science I am now teaching high school students ophthalmic fabrication skills in a high poverty area. I am hoping to be able to eventually dispense prescription glasses to students who can't afford them, but I need to obtain my optician certification to do so. I've passed the ABO, but now I have a state practical coming up and one of the things I will probably have to do is neutralize a progressive. I've done a couple, but I want the official way others do it to help me procatice. Any information you can give will be greatly appreciated.

    Thank you for your help

  2. #2
    Rising Star
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    The easiest was is to use the Progressive identifier book. Identify the progressive, put the markings on and then check from there.

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    yes, but...

    Thanks for the replies. Here is my thing - I was told that I should turn the lens around, find the distance power and then the add power and find the difference between the cyl powers. I've always found the difference between the spheres. Which is correct? Also, my readings almost always come out different than the power marked on the lens. Why? Thanks again

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    Compulsive Truthteller OptiBoard Gold Supporter Uncle Fester's Avatar
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    Last edited by Uncle Fester; 04-08-2013 at 03:31 PM. Reason: self delete...

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    Compulsive Truthteller OptiBoard Gold Supporter Uncle Fester's Avatar
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    Sorry but I'm calling it like I see it.

    If you don't know why or when you should take powers from the convex side of a lens you should get a copy asap of Brooks and Boorish "System for Ophthalmic Dispensing".


    You really really need a mentor to show you. Find a local optician and offer to pay them for their time for a couple of hours training. I'd postpone the practical as you seem lost with some very basic skills that will have you failing the test.

    I believe NY has one of the tougher exams or at least they used to.

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    [QUOTE=Uncle Fester;457118]Sorry but I'm calling it like I see it.

    If you don't know why or when you should take powers from the convex side of a lens. [\QUOTE]

    Im sorry for the misunderstanding. I was asking if the difference should be measured between the sphere powers or the cyl powers. The optician I worked with last week said the cyl powers, but I am seeking to account for the difference between my knowledge nd what I was told. Imwas also trying to find out why my progressive por reading is usually different from that stamped on the lens. Thank you for the very helpful reply and support

  8. #8
    Master OptiBoarder rbaker's Avatar
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    Where are you located? If you are close by I will be happy to spend a few hours with you at no charge. If we knew what neck of the woods you were located in perhaps some other OptiBoarder would offer a similar deal.

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    Bad address email on file Randle Tibbs, ABOM's Avatar
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    [QUOTE=NewmanSpecials;457128]
    Quote Originally Posted by Uncle Fester View Post
    Sorry but I'm calling it like I see it.

    If you don't know why or when you should take powers from the convex side of a lens. [\QUOTE]

    Im sorry for the misunderstanding. I was asking if the difference should be measured between the sphere powers or the cyl powers. The optician I worked with last week said the cyl powers, but I am seeking to account for the difference between my knowledge nd what I was told. Imwas also trying to find out why my progressive por reading is usually different from that stamped on the lens. Thank you for the very helpful reply and support
    You should use the difference between the sphere readings. As far as the powers not reading the same as what is stamped; it could be two things, not reading the power in the correct position and secondly, some manufacturers are only giving approximately 85% of the total reading power stamped on the lens.

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    [QUOTE=Randle Tibbs, ABOM;457174]
    Quote Originally Posted by NewmanSpecials View Post
    some manufacturers are only giving approximately 85% of the total reading power stamped on the lens.

    Thank you for the clarification! Can you give me any reason why manufacturers would do that? And how should I know if they are doing that

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    Master OptiBoarder NCspecs's Avatar
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    [QUOTE=Randle Tibbs, ABOM;457174]
    Quote Originally Posted by NewmanSpecials View Post

    You should use the difference between the sphere readings. As far as the powers not reading the same as what is stamped; it could be two things, not reading the power in the correct position and secondly, some manufacturers are only giving approximately 85% of the total reading power stamped on the lens.

    Are you referring to freeform lenses with the compensated add power stamped in the lens instead of the actual perscribed add?
    "Strictly speaking, there are no enlightened beings; only enlightened activity." -Shunryu Suzuki

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    [QUOTE=NCspecs;457275]
    Quote Originally Posted by Randle Tibbs, ABOM View Post


    Are you referring to freeform lenses with the compensated add power stamped in the lens instead of the actual perscribed add?
    Yes. When i neutralize the lens at the near verification circle the powers are often off from what is stamped. For instance, I just worked with a lens stamped 27, but I read it at +2.50. I understand that I should go with the reading stamped on the lens, but this makes me question whether I am reading the lens correctly. I don't have the prescribed power of these glasses, so how do I know that my reading is accurate if I am reading the near incorrectly.

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    You will see that a lot anymore with the smaller frames. Unfortunately, sometimes the add gets cut off. That is why it is important as an Optician to use the right Progressive lens for the RX and the frame.

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    Compulsive Truthteller OptiBoard Gold Supporter Uncle Fester's Avatar
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    I'd trust the stamped add. If the test uses custom progressives to be read I'd cry fowl as the labs supply that info on the order/invoice. Reading power to .01 of a diopter can't be accurately done with our current lensometers as the aperture only will produce inaccurate readings..

    Remember to zero out the lensometer before starting!

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    [QUOTE=NewmanSpecials;457282]
    Quote Originally Posted by NCspecs View Post

    Yes. When i neutralize the lens at the near verification circle the powers are often off from what is stamped. For instance, I just worked with a lens stamped 27, but I read it at +2.50. I understand that I should go with the reading stamped on the lens, but this makes me question whether I am reading the lens correctly. I don't have the prescribed power of these glasses, so how do I know that my reading is accurate if I am reading the near incorrectly.
    Lens manufacturers want to sell as many of their lenses as possible so they say you can fit them at lower seg heights. They reason that wearers can get by with only 85% of their prescribed add. So in many cases much of the reading area is cut off, and the add power reads lower.

    Also if you are reading an unknown progressive design, you don't know how far the drop is from the PRP to the full reading power. Corridor lengths can vary widely.

  16. #16
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    That's where identifying and using the lens layouts in your progressive book come in handy. Dot up the lens according to the matching layout and you can see if the add has been cut off.

  17. #17
    Master OptiBoarder OptiBoard Gold Supporter Judy Canty's Avatar
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    Quote Originally Posted by IhaveSpecialEyes View Post
    That's where identifying and using the lens layouts in your progressive book come in handy. Dot up the lens according to the matching layout and you can see if the add has been cut off.
    If you're talking about using the "layout" printed in the OLA Progressive Lens Identifier, they are NOT accurate for measurements.

  18. #18
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    No the layout itself is not but by using the min fitting height you can get a good idea of whether or not you have most of the add cut off.

  19. #19
    One eye sees, the other feels OptiBoard Silver Supporter
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    Quote Originally Posted by Uncle Fester View Post
    I'd trust the stamped add.
    Yup. It pretty much has to be right. Good thing too because measuring it is so problematic considering the aperture size at the lens stop and with compensated designs.
    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.



  20. #20
    OptiWizard
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    Where are you in NY? I'll match rbaker on his offer. If youre close to NEPA i'll be happy to show you what i know pro bono. It's simpler than you're imagining it to be.

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    Passed

    Quote Originally Posted by Jason H View Post
    Where are you in NY? I'll match rbaker on his offer. If youre close to NEPA i'll be happy to show you what i know pro bono. It's simpler than you're imagining it to be.
    Hi All- i wanted to say thanks for your help. I passed the exam with a 93. I'm running a high school program teaching students to make glasses, so it really helps me help my students (both in the class and in the school) to have the certification.

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