The title says it all. What would the person be able to see?


By harmless, I mean that it is non-corrosive, non-toxic, etc. The liquid doesn't cause any biological damage to the eye or any other organ related to it, simply put.

  • $\begingroup$ It would not be appreciably different. The humours are sometimes replaced temporarily in surgery (after which they naturally reform). $\endgroup$ – Steve Feb 11 '18 at 11:21
  • $\begingroup$ @Steve Presumably they're replaced with a fluid of the same refractive index, though? $\endgroup$ – Chris Feb 11 '18 at 11:22
  • $\begingroup$ @Chris, yes saline matches the refractive index of the natural humours fairly closely (though not exactly). $\endgroup$ – Steve Feb 11 '18 at 13:16

If it's significantly different, then not a whole lot. Your vision is very sensitive to the focal length of the lens of your eye, and changing the refractive index of the fluids in your eye changes that focal length. Depending on the refractive index, it would just make you nearsighted or far

The focal length of a lens depends on its refractive index, and the refractive index of the media on both sides, so opening your eyes underwater does a similar thing. Relevant: Eyes open under water.

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  • $\begingroup$ So effectively, you'd need a change in your prescription glasses. It's interesting to note that you'd immediately be able to see clearly underwater (without a change in your habitual focus) by wearing glasses (which you may not need at all when looking through air, or would have a different prescription than in air). $\endgroup$ – Steve Feb 11 '18 at 13:14
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    $\begingroup$ @Steve It would also the ability of your eyes to focus over a range of distances, though. So at a minimum you'd probably need bifocals or something similar. $\endgroup$ – Chris Feb 11 '18 at 13:27
  • $\begingroup$ I do wonder, though, if one would be able to sense IR or UV light, because the eye is a wavelength detector, and altering the fluid in the eye would change the wavelength perceived. $\endgroup$ – Harry Weasley Feb 11 '18 at 16:17
  • $\begingroup$ @Chris what if one wears the required corrective lenses? Would one be able to sense UV or IR light, as the eye is a wavelength detector? $\endgroup$ – Harry Weasley Feb 11 '18 at 16:24
  • $\begingroup$ @HarryWeasley Your eye detects the energy of photons, not the wavelength directly. Changing the medium inside your eye changes the wavelength, but not the energy of each photon. $\endgroup$ – Chris Feb 11 '18 at 22:10

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