Lens thickness

Discussion in 'Optometry Archives' started by Mike, Jan 3, 2008.

  1. Mike

    Mike Guest

    Are there any tools online for giving a rough idea how thick glasses
    lenses will be at their thickest point given the prescription, size of
    lens and lens type? I've ordered some 1.67 thinnest lenses online and
    these are much thicker a pair from an almost identical prescription with
    normal 1.57 thickness I ordered from the same place a year ago (as they
    were just meant to be temporary!). I do admit the lenses in my latest
    pair are widerr, but at the point where the others would have stopped
    (from the middle out) they are about the same.

    I've always gone for high index and am used to what size they roughly
    end out at, but to me these don't look right. This was as part of an
    order of 2 pairs (along with a reading pair with a +1.00 Add) and they
    are insisting the distance pair are correct from the one email they've
    responded to. Now they seem to be refusing to answer my emails!
    Mike, Jan 3, 2008
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  2. Mike

    Mark A Guest

    If you have a progressive lens, there are etchings on the lens that will
    reveal (almost always) the lens model, material, and index of the lens.
    Check it out and make sure you actually got a 1.67 lens. You will have to
    have a progressive lens identifier guide (the actual index numbers are not
    etched on the lens) to decipher it, or take it to a local optician and ask
    them to check it.
    Mark A, Jan 3, 2008
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  3. You've pretty much answered your own question, in admitting the thick
    lens is the wider one (as always), but for verification, click on:


    w.stacy, o.d.
    William Stacy, O.D., Jan 4, 2008
  4. Mike

    Mike Guest

    In message <eqifj.33362$>
    Neat tool - thank you. For lens size, do you measure diagonally at the
    longest point, or across at the longest point?

    Actually when comparing these there is very little difference in size -
    maybe a couple of mm. Because the top edge of the lens is wider than
    the bottom edge in both pair, one pair looked bigger than the other when
    I held one above the other

    For some reason my last pair from them seem to be thinner than the tool
    predicts and I didn't pay extra for thin lenses (I still have my email
    to them to prove it)
    Mike, Jan 4, 2008
  5. Mike

    Mark A Guest

    There are things that can make one lens thinner than another even with the
    same material. These include whether the lens is aspheric (as opposed to
    spherical), and of course the frame size.
    Mark A, Jan 5, 2008
  6. Mike

    Mark A Guest

    The term "high index" has no real meaning anymore since there are so many
    different indexes available now. At one time the most common material was
    1.50 index and 1.60 or polycarb (1.59) were considered high index, but now
    1.67 is quite common (and sometime the only index available in certain
    models), and there are even higher indexes available.

    So unless you know exactly what index lens you had to begin with,
    speculating about whether a different (unspecified) index lens will make it
    any thinner is like a dog chasing its tail.
    Mark A, Jan 5, 2008
  7. Mike

    Mike Guest

    Are you saying the same prescription lenses can be different thicknesses
    on the same index but made with different plastics? If I post pictures
    would someone be happy to give an opinion
    Mike, Jan 6, 2008
  8. Mike

    Mark A Guest

    No, not even different plastics. The lenses can have a differenct thickness
    even with the same plastic if one is aspheric design and the other is
    spherical design. Also, the size of the frame makes a difference.
    No, you need to go back to your optician and find out what lens
    manufacturer, lens design, and lens material are. Looking at pictures will
    not suffice.
    Mark A, Jan 7, 2008
  9. You measure horizontally. If you fit a lens precicely into an rectangle
    that is oriented so that the widest dimension (length) is on the
    horizontal, the horizontal measured in mm is the "eye size". The
    diagonal measurement you mention is useful to lens grinders, and often
    the thickest part of the lens is found on this diagonal.
    William Stacy, O.D., Jan 7, 2008
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