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Thread: Plus power creeps into distance?

  1. #1
    OptiBoard Professional lab fly's Avatar
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    Plus power creeps into distance?

    We have noticed for years that when we process a plus powered PAL, with a small B and a distance AOC of 12 or less that some of the plus power "creeps" up into the distance by an 1/8 or so. We have never had any offices or their patients complain but it is on all platforms. We have seen it on Zeiss, Shamir, IOT, and Seiko. I have a thought in my mind why it happens but does someone have a better scientific reason? Thanks

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    OptiBoardaholic OptiBoard Bronze Supporter
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    I have noticed when I order Shamir Auto2+ pals from one of our labs I will get a tiny bit of plus in the distance but when I order the same design from another lab we use the powers are usually spot on.

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    Master OptiBoarder OptiBoard Silver Supporter lensmanmd's Avatar
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    Are you providing POWs, or relying on avg calculations?
    I bend light. That is what I do.

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    Induced power as you described as .12 is typical if lens power is a strong plus as thickness will result in magnification.

    Also, since it seems the progressive is "squeezed" into frame the optimum area to read distance Rx might be in the edger

  5. #5
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    Years ago, when the Shamir rep would show me progressive plots of various progressive designs, almost all "short corridor" PALs would exhibit increased peripheral unwanted power in the distance. I would always caution patients who wanted to use a small B frame for progressive use due to this.

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