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Thread: Tint affecting lensometer reading?

  1. #1
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    Tint affecting lensometer reading?

    Just wanted to pose this question to my esteemed colleagues-in-arms.

    I had a patient that came in earlier this week asking for a progressive lens design and a light (~25%) yellow tint added. The patient's script is pretty straightforward:

    -2.50 D.S. OU +2.50 Add

    The first time when I did my final inspection when the job came in last week, both lenses seemed under-minused (I read about a -2.00 OU) and sent the order back for not passing ANSI standards. Today, the re-made lenses came back and the lenses are reading:

    -2.25 -0.25 x071
    -2.25 D.S.

    The lens design that we ordered is NOT compensated. Our lab does good work and this a pretty unusual situation to come across, so before I call the lab manager about this, I was wondering if the yellow tint is affecting how I'm reading the rx through the focimeter (or lensmeter or vertometer, depending on your vernacular). Maybe I'm over-thinking this, but would the yellow tint, in its blue-blocking capability, be under-minusing the lenses since it's attenuating lower frequency visible light? Is that a stupid question?

  2. #2
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    I think no... the tint block some light but the light that can pass is
    diverted through the minus lens.

    Also focimeter use infrared light o green light.

    Try to Remark the engravements to guide the lens reading point.

    If possible try manual lensmeter also.

  3. #3
    Master OptiBoarder CCGREEN's Avatar
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    Make sure you haven't plowed right through step #1 lensometer 101, I am guilty of this.......focus the eye piece of your reading instrument whatever it may be. And then a .25 power difference can just the difference between your eye vs my eye vs equipment calibration.

  4. #4
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    A few considerations:

    1. If you lenso is rounding to the nearest 0.25D, the original lens could have been -2.40D and the tint shifted it just a bit, say to -2.35D, enough to round it to -2.25D, instead of -2.50D. I see A LOT of that in returned lenses.

    2. If the tint is a coating (poly), I wouldn't be surprised if the coat itself is thick enough to change the curvature a little bit. Given that you read some cyl, the process might have created irregularities on the surface or the original lens.

    3. If the lens material is porous and the tint is meant to be absorbed by the lens, like a CR-39, I wouldn't be surprised if the tint effectively changes the index of refraction of the lens. Index of refraction is a function of the speed of light in the medium. If you change the medium, you change the speed of light within it and thus the index of refraction. Of course that depends on the chemical compound used to achieve the desired colors.
    Vitor Pamplona
    CEO, EyeNetra Inc

    Come check our autorefractor, lensometer and phoropter.

  5. #5
    One eye sees, the other feels. OptiBoard Gold Supporter
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    Quote Originally Posted by grudyfan13 View Post
    Maybe I'm over-thinking this, but would the yellow tint, in its blue-blocking capability, be under-minusing the lenses since it's attenuating lower frequency visible light?
    No.

    Some of the very soft design PALs will let some of the add power creep into the distance reference point- make sure you measure at that point, typically 4mm to 6mm above the fitting cross, using the manufacturer's mask, or with a mask that has a very small distance zone aperture. Remove the lenses if the frame interferes with the lens resting flush on the lens stop.

    Hope this helps,

    Robert Martellaro
    Roberts Optical Ltd.
    Wauwatosa Wi.
    www.roberts-optical.com
    ~~~~~~~~~~~~~~~~~~
    Science is a way of trying not to fool yourself. - Richard P. Feynman

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