Question about Glass, Plastic, Trivex, polycarbonate lens and safety

Discussion in 'Optometry Archives' started by C, Jan 8, 2008.

  1. C

    C Guest

    I can't find my perscription, but if memory is correct, both eyes are around
    +3 with no astigmatisms. My current glasses are polycarbonate lens. Before
    them, I had glass. I noticed a drop in "brightness" with the polycarbonate
    lens. Would Plastic or Trivex make the lens brighter? How "unsafe" is
    glass? My glass lens up until this time were bullet proof i.e. they took a
    lot of bumps. And even if a lens was to shatter, would the eyelid not close
    in time to protect the eye? I have to think that my eyes behind a glass
    lens are infinitely more protected than the guy that doesn't wear glasses of
    any kind......


    C, Jan 8, 2008
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  2. C

    Mark A Guest

    Forget about glass. It is too heavy.

    Trivex would be great if you don't mind slightly thicker glasses. 1.60
    Plastic would be about the same thickness as polycarb, but much better
    optical qualities. Polycarb does have tendency to scratch easily or slight
    fog if inappropriate chemicals are applied.

    Getting a high quality (durable) AR coating will make your vision brighter
    (it lets more light pass through the lens by reducing reflections).

    Anytime you avoid polycarb, your vision will improve.
    Mark A, Jan 8, 2008
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  3. C

    p.clarkii Guest

    Glass certainly does seem to have an excellent optical quality, and
    it's durable to scratching. As I recall, there is such a thing as
    safety glass lenses. They are made a little thicker than normal, and
    then are tempered with either a heat (baking) or chemical treatment.
    They pass all OSHA standards just like safety polycarb and plastic,
    although they would be quite a bit heavier for sure. See your eyedoc.
    p.clarkii, Jan 8, 2008
  4. C

    Mike Ruskai Guest

    All this is more than a bit alarmist. I had glass lenses for over 10
    years, starting at age 10. They were heavier, and I'm sure they
    wouldn't stand up the same abuse as something like polycarb, but they
    were not nearly as fragile as you imply.

    And there are no needle like shards of glass projected back from
    windshields. I had an aluminum boat driveshaft crash through mine a
    few years back at 75mph. All of the glass that broke free was

    The only real argument against glass lenses is weight. Any face plant
    that would break them is going to cause more serious injuries first,
    as I can attest from experience (none of mine ever broke).
    Mike Ruskai, Jan 8, 2008
  5. C

    Mark A Guest

    Windshields are made completely differently. They have a lamination in the
    middle of two sheets of glass that holds it all together to reduce serious
    injury when it breaks.

    The reasons why you want glass lenses are not sufficient. Just avoid
    polycarb and you will be happy with the lenses.
    Mark A, Jan 8, 2008
  6. C

    The Real Bev Guest

    When I face-planted I broke the frame above the right lens (which I
    repaired with super glue), but the lenses were fine. I used glass
    glasses (photochromic) as motorcycle glasses for at least 15 years with
    no mishaps. The bee that bounced off a lens and then into my helmet,
    giving me a nasty sting in the process, probably shouldn't count anyway;
    bees are pretty soft.

    They really WERE heavy, though -- and those were the days when glasses
    were BIG.
    The Real Bev, Jan 8, 2008
  7. C

    The Real Bev Guest

    Their photochromic ability was WAYYYY better than what I got with
    plastic a few years back. The plastic photochromes were essentially
    worthless while the glass ones worked just fine.
    BUT the thin polycarb that non-prescription lenses are made of works
    quite nicely -- my favorite sunglasses (the ones I wear with my
    contacts) are cheap ($5-$7 on sale) polarized ones from Big 5 (discount
    sporting goods store) and are light and cover a lot of area, making them
    good for wind-in-the-face occasions.
    The Real Bev, Jan 8, 2008
  8. Agreed PC has a poor Abbe, but that is an increasing problem
    at higher powers and not for plano like Bev's sunglasses.
    Did I miss something?

    -- Robert
    Robert Redelmeier, Jan 9, 2008
  9. And also don't exist in plano polys or near plano ones, which make great
    sunglasses. I like the big poly wrap arounds with the Rx inserts...
    best of both worlds.

    I use polys pretty routinely in kids, esp. in situations where insurance
    pays for them but not for Trivex. Kids don't seem to mind the chroma.

    re the glass +3 lenses, if his nose can handle the weight, they're
    pretty safe.

    In wwII, the soldiers who wore glasses often had drilled glass lenses,
    1.0 mm ct, no tempering. That's why they are called glasses, after all...

    one last item from an old o.d.'s memory: the optically best glasses I
    ever wore were glass, with cruxite A tint in the glass and
    anti-reflection coating. Far less reflection than any of today's
    lenses, just about zero ghosting, and almost unscratchable.

    My nose was stronger then...

    w.stacy, o.d.
    William Stacy, O.D., Jan 9, 2008
  10. Agreed. Thanks for the explanation.
    I may be misinterpreting you, but chromatic abberation most
    certainly can exist on the principal optic axis. Abbe number [wiki]
    is a measure of how different the material's refractive index is
    at different visible wavelengths (colors). How far apart the focal
    points are for different colors, hence how big the chroma haloes.

    Off axis is is worse (prism rainbows), and at higher powers
    linearly worse: more defraction means more dispersion.

    In photographic lenses, negative and positive elements with
    different RIs and Abbes are combined to cancel out as much
    of the chromatic abberation as practical.

    What I don't know is how the human eye system is wrt chromatic
    abberation (RI & Abbe of lens and vitrious humor). I suspect it
    is not fully compensated and does corrections by cone placement.

    -- Robert
    Robert Redelmeier, Jan 9, 2008
  11. Obviously no distance at all. However, neglegible amounts of
    light actually pass through the center of a lens. Technically
    zero. Most passes through the periphery where refraction is
    required. Whence un[der]corrected vision worsening in low light.

    Correct. I misspoke -- too much work with the grates!

    That is what I'm suggesting, or that the phtosensitive
    portions of the cones are biased to compensate for ab.
    This is well known and has little bearing on ab.
    Certainly these features exist but I'm not sure they have a
    positive effect on ab: to the extent it matters (the fovea
    is small and hence relatively flat), hemispherical focus
    planes require more refraction than equivalent flat-plane.
    Aspheric lenses still have chrom.ab and are more used to
    fight spherical abberation and intensity fall-off or for
    improved off-center use in glasses.

    -- Robert
    Robert Redelmeier, Jan 9, 2008
  12. C

    Mike Ruskai Guest

    1) I wasn't comparing glass lenses to car windshields. The person I
    was responding to did, and in doing so made an incorrect claim about
    windshields. I was correcting that.

    2) I don't want glass lenses. I simply said that there's no
    legitimate safety argument against them, and that weight is the main
    reason you'd want to avoid them.
    Mike Ruskai, Jan 9, 2008
  13. C

    Mike Ruskai Guest

    This is true for the lenses themselves, but not the wearer. You get
    color fringes in the center of your vision if you move your eyes
    instead of your head.
    Mike Ruskai, Jan 9, 2008
  14. C

    C Guest

    Awesome responses! Thank you,

    C, Jan 11, 2008
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