Reflections of Light in Contact lens

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Discussion Overview

The discussion centers on the reflections of light in contact lenses, particularly focusing on the effects of varying indices of refraction and the implications for uncoated surfaces. Participants explore the optical properties of contact lenses, including the impact of tear film and material composition.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants assert that reflections can reach 4% for uncoated surfaces, questioning whether this applies to thin contact lenses as well.
  • Others agree that the exact reflection depends on the material of the contact lens, noting that there are various types of materials used.
  • A participant raises the question of whether contact lenses can be considered uncoated, considering the presence of tear film on the lens when in use.
  • It is mentioned that the refractive index of tear film varies between 1.334 and 1.336, while soft contact lenses typically have a refractive index of about 1.412 to 1.424.
  • There is a suggestion that thin-film interference may be relevant due to the presence of tear film on both sides of the lens.
  • Participants note that the thickness of the tear film and the hydrogel contacts can influence the optical properties, with specific measurements provided.

Areas of Agreement / Disagreement

Participants generally agree on the influence of material composition and tear film on reflections in contact lenses, but there is no consensus on the specifics of reflection percentages or the implications of thin-film interference.

Contextual Notes

The discussion includes various assumptions about the refractive indices and the conditions under which reflections occur, but these assumptions are not fully resolved. The impact of different materials and the role of tear film introduce additional complexity that remains unaddressed.

cube137
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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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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?
 
cube137 said:
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?

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.
 
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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