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B Reflections of Light in Contact lens

  1. May 2, 2016 #1
    It is said that whenever index of refraction varies, there are reflections and it can reach 4% for uncoated surfaces.. how about in thin contact lens used for eyes.. is there also 4% reflection on each surface if they are uncoated?
     
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  3. May 2, 2016 #2

    Simon Bridge

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    The short answer is "yes". The exact reflection depends on the material the contact is made out of.
    examples: http://www.ncbi.nlm.nih.gov/pubmed/3231673

    But can contact lenses be uncoated? i.e. what about the liquid on your eyes, does that coat the contact lens?
     
  4. May 3, 2016 #3

    Andy Resnick

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    It depends on what the contact lens is made of- there are lots of 'flavors':
    http://www.allaboutvision.com/contacts/faq/contact-materials.htm

    And as Simon Bridge points out, there is a tear film that cover the lens when it is in your eye, so the refractive index mismatch is fairly small.
     
  5. May 3, 2016 #4

    Simon Bridge

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    Tear refractive index between 1.334 and 1.336 (±0.0011) depending on salt content.
    http://www.ncbi.nlm.nih.gov/pubmed/8570161

    Refractive index of "soft" contact lenses about 1.412 to 1.424 (±0.0005 typ uncertainty) depending on material.
    http://www.ncbi.nlm.nih.gov/pubmed/20009942

    Maybe there is a thin-film interference question in there?
    The lens has tear-water either side of it about 2.3##\mu## m thick.
    http://www.otticamartini.it/wp-content/uploads/2014/03/68.full_.pdf
    ... the hydrogel contacts in the above paper are typically 5-6##\mu## m thick.

    Unsurprisingly these things are studied in painstaking detail.
     
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