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Thread: brush up on verifying progressives with manual lensometer

  1. #1
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    brush up on verifying progressives with manual lensometer

    Does anybody have any tips or procedures that have stood the test of time for accurately neutralizing an RX on a standard pprogressive lens with a manual lensometer. Other than marking the lens, and checking the center the distance and near reference points, what else should be done. I was never really properly trained in this area.

    For instance, when I usually check the DRP, the intersection of the mires are usually below the center of the reticles, sometimes almost out of sight. Do you just raise the tray until the mires are centered in the reticles? And if that is done, when you check the other lens what happens if the mires are not centered again?

    Also, what is the proper use of the auxillary prism ring in neutralizing a progressive lens? When initialing neutralzing the lens, do you twist the knob until the mires come centered? And if so, when you check the other lens, shouldn't it be centered?

    Furthermore, how does induced prism affect checking the RX. What about high cyl, sphere power? Any input would be greatly appreciated. Thanks guys

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    neutralizing PALs

    Hi Rolandclaur,

    A simple way to remember is to do the very same thing you do for bifocals, but add one more step:

    Step 1: Neutralize the distance portion as you normally would, with the exception of vertical centration. You can center the mires horizontally, but don't worry about vertically (yet). This is due to prism thinning, and, since vertical prism cancels, no big deal.

    Step 2: Center the mires vertically (even though the sphere and cyl lines will blur slightly), and spot. Verify that there is no vertical imbalance between the OD and OS (starting with the strongest one at 90 is important). Anything outside 1/3 ^ is too much.

    Step 3: Neutralize the near add at the nearpoint markings, as you would for a bifocal, turning around for higher powered lenses.

    The only difference is the distance vertical centration part...have to add another step to verify that there is no imbalance between the two lenses.

    And, to visually inspect the PAL, hold it up to a grid pattern:

    1. Move the lens up and down to see progression in magnification/add.

    2. Move the lens back and forth to see the design.

    : )

    Laurie

  3. #3
    One eye sees, the other feels OptiBoard Silver Supporter
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    Quote Originally Posted by rolandclaur
    For instance, when I usually check the DRP, the intersection of the mires are usually below the center of the reticles, sometimes almost out of sight. Do you just raise the tray until the mires are centered in the reticles?
    No, you should use the prism to center the image. Use a base down prism for minus powers and base up prism for plus.

    And if that is done, when you check the other lens what happens if the mires are not centered again?
    Same as above. Vertical prism imbalance is checked at the MRP (main reference point), also called the PRP (prism reference point), located on the 180 line, 17mm equidistant from the circle or symbol engravings. An equal amount of base down prism indicates prism thinning incorporated into the grind or PAL design.

    Regards,
    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.



  4. #4
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    Maybe I'm misunderstanding the question, but we always check the prescription on progressives by first marking the 2 side spots which are 17mm apart and are seen on a backlighted grid. We then position the lens over a template and mark the fitting cross located a few millimeters above the center. We then read the add which is written under side marking spot. We then look at the logo and check it in the OLA book to derive the actual progressive and lens material used.

    It's a rather cumbersome way of doing it but I think it's probably more accurate than any other way.

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