anti reflective coating?

Discussion in 'Optometry Archives' started by dumbstruck, Jan 14, 2011.

  1. dumbstruck

    dumbstruck Guest

    Ever noticed how many older folks have brown patches burned into their
    upper cheekbone? It is immediately below the glasses and exactly where
    a downward reflecting sun hits.

    So I wonder if anti reflective coating on outside of lenses is a good
    idea for a preventative. It seems comparable to the times I walk along
    a waterway when the water is riffled by wind vs calm - sun reflecting
    off the calm can be brutal.

    But I distrust coatings, which may make cleaning a problem and may not
    age gracefully. Opinions?
    dumbstruck, Jan 14, 2011
  2. dumbstruck

    dumbstruck Guest

    Interesting, but since most glasses are curved inward and are (or
    should be) canted a bit downward... I think the bounce is from a lower
    sun angle that hits the lense so low that it doesn't have to much
    distance (and thus divergence) to the skin spot in question. And I
    don't think it comes from sunburn, so may not strictly be UV but
    rather some long term response to a slight differential of light.
    Maybe somewhere on web there are portraits of the problem from a
    dermatology point of view that sheds some (ahem) light, maybe of
    sunblasted faces of Australian blondes or redheads.
    dumbstruck, Jan 15, 2011
  3. dumbstruck

    Mark A Guest

    No, never noticed it.
    If the lens already reflects UV, I doubt an AR coating would add much
    aditional protection.
    If you get one of the factory coatings like Zeiss Caret Advantage, Essilor's
    Crizal, etc, then they are quite durable if you don't abuse them. Quality AR
    coatings are also available from other lens manufacturers.

    The coatings applied by local optical shops are much more fragile and cost
    more in the long run because you often will have to replace your lenses
    before your Rx changes.
    Mark A, Jan 15, 2011
  4. dumbstruck

    dumbstruck Guest

    I'm not talking about the traditional areas that are dabbed with
    glacier cream due to sun exposure... such as nose and the whole span
    of the upper cheek. Just some small oval spots that mimic glasses yet
    sit immediately below them. Can't find good pictures of this on the
    internet though.

    Some snooping on internet suggests they may be melasma, which isn't
    just from sun but a combination of sun and unusual hormone activity
    (such as from birth control pills or pregnancy). But this still
    doesn't seem to match what I see among the public. Guess the evidence
    doesn't support a class action lawsuit against the opto world though -
    dumbstruck, Jan 15, 2011
  5. dumbstruck

    dumbstruck Guest

    Thanks, sounds like an expense with questionable payoff, unless I
    expect to face TV lights or something. If it is a melasma issue,
    wikip* sez the upper cheek would be an issue mainly for "men and women
    of German/Russian and Jewish descent" with out of tune hormones,
    thyroid, or...
    dumbstruck, Jan 15, 2011
  6. dumbstruck

    Mark A Guest

    Your conclusion is invalid. AR coating will improve your vision in almost
    all lighting situations. AR coating was invented by Zeiss for camera lenses
    many years to improve the quality and resolution of photographs (cameras
    don't get sunburn).
    Mark A, Jan 16, 2011
  7. dumbstruck

    dumbstruck Guest

    Wow, I think I will give it a try next time. Although I think eyeglass
    glare coatings aren't functionally the same as, say, telescope anti

    And I will get the cheap stuff, which probably won't have the crud
    repellant layer they talk about. I had a terrible time with an anti
    scratch coating long ago which wouldn't clean well and came off in

    But a good experiment to check the claimed anti glare properties for
    nighttime, etc.
    dumbstruck, Jan 16, 2011
  8. dumbstruck

    dumbstruck Guest

    Look at the lowermost part of the lense - it curves in toward the
    skin. Look at the skin below which it is almost touching. This faces
    upward, giving something in the rough vicinity of a right angle for
    the sunlight to bounce.
    \ =lense
    / =cheek
    Just talking about a third of an inch bounce to a browned hotspot just
    below lowest part of lense. The physics seem similar to a solar oven.

    My observations are for light skinned community living considerably
    closer to the equator than say Key West. Clouds are rare, and with the
    sun like a year round xray machine, you become aware of ravages of
    even reflected sun. A concave angle on a light colored building can
    create a solar hotbox - not sure if it is IR, UV or what. Old folks
    get "age" spots like crazy, but it seems more than coincidence how
    many line up just below eyeglasses.
    dumbstruck, Jan 16, 2011
  9. dumbstruck

    Mark A Guest

    No, that is not correct. They ARE functionally the same. To quote the
    Wikipedia article link you posted regarding AR coating for glasses
    (ophthalmic use):

    "Allowing more light to pass through the lens also increases contrast and
    therefore increases visual acuity."

    This is exactly the same reason why AR was originally invented for camera
    and telescope lenses.
    I would classify AR coatings as 3 "levels"

    - Cheap stuff - will not last long, and will scratch, peel, or discolor
    - Good Stuff applied at manufacturer lab - much more durable than the cheap
    - Good Stuff and easy to clean (often with Teflon, etc) - durable and easy
    to clean (these are two different attributes)

    So if you get the cheap stuff, don't expect it to last. I would recommend at
    least "the good stuff," even if you don't get the "easy to clean" variety.
    Mark A, Jan 17, 2011
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