accuracy of measuring lenses

Discussion in 'Optometry Archives' started by denaman, Feb 2, 2007.

  1. denaman

    denaman Guest

    Say, how accurate is it when Lenscrafters takes your existing pair of
    glasses, takes them back in the lab, and measures the lenses? Are
    they able to precisely read your existing prescription, or is there a
    lot of variation?

    The reason I ask is because they did precisely this and came up with a
    -6.50 reading on one lens (I'll keep it to the one lens to keep it
    simple), whereas I believe all my prescriptions are higher than that,
    but can not be sure because perhaps I've misplaced one. And I don't
    know which paper prescription belongs to these lenses.

    One more question. As you go from say -6.50 to -7.00 to -8.00, are
    these marginal jumps perceptually. By that I mean if I go from one to
    the next would the prescription be just a hair better or is it a stark
    difference?

    I have a case where I'm perfectly happy with my current prescription,
    which Lenscrafters is saying is -6.50. Went to the eye doctor last
    month and got my eyes checked and she said that my right eye is
    -8.00. Now I don't want a pair of binoculars strapped to my head if I
    don't need them; I really don't need to see the cracks in the paint on
    the house across the street. So, I was going to go with a six year
    old prescription that gave a lower reading of -7.00. That was why I
    was interested in my existing prescription; I wouldn't want to go
    backwards and spend all that money on a worse prescription.
     
    denaman, Feb 2, 2007
    #1
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  2. denaman

    Dan Abel Guest


    Last time I tried this, it didn't work too well. I'd recommend an exam.


    Call the doctor's office. They should have records.


    There's a difference. Some people are OK with it and some aren't.

    The doctor gets money for determining the best prescription. I think
    it's negotiable.
     
    Dan Abel, Feb 2, 2007
    #2
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  3. denaman

    Bucky Guest

    they're not that accurate.
    if you can see 20/20 at -6.50 without eyestrain, then stick with it.
     
    Bucky, Feb 2, 2007
    #3
  4. denaman

    Dom Guest


    There can be a margin of error, but you wouldn't expect it to be more
    than about 0.25 dioptres at -6.50. This probably correlates pretty well
    with the jnd (just noticeable difference) during refraction for most
    patients with this degree of myopia.

    This leads to the answer to your second question: a change of 0.50
    dioptres should for most people be quite obviously noticeable... UNTIL
    you reach your correct refraction, after which further increases will
    probably look different but not clearer.

    At these higher powers the frame fitting (i.e. distance from eyes, and
    angle of lenses to face) and lens type (i.e.
    index/asphericity/material) starts to become more important than 0.25
    dioptres here or there.

    Dom
     
    Dom, Feb 2, 2007
    #4
  5. denaman

    denaman Guest

    Thanks guys. That helps.
     
    denaman, Feb 2, 2007
    #5
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