Reflections of Light in Contact lens

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Main Question or Discussion Point

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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Simon Bridge
Homework Helper
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?

Andy Resnick
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':

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.

Simon Bridge
Homework Helper
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.
... the hydrogel contacts in the above paper are typically 5-6$\mu$ m thick.