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Would putting a dye on my eyeball to make my sclera (the white of my eye) turn black bring any advantages?

I know that wearing black around the eyes reduces glare (as in that functional makeup some athletes wear), and you can see eyes surrounded by black has evolved on animals that hunt in sunny areas, e.g. the cheetah.

I wonder what would be different about a world viewed from eyes with black sclerae and a world viewed as we normally see it.

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    $\begingroup$ "a world viewed from eyes with black sclera"? We don't view anything from our sclerae. Light enters our eyes via our pupils which then hits our retinas. Changing the color of your sclerae (such as with novelty sclerae contact lenses or with dye) doesn't affect your vision. $\endgroup$ – AngelPray Jan 25 '18 at 19:10
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    $\begingroup$ The only benefit is if you're in an infantry charge, and the defenders have been told "Don't fire until you see the whites of their eyes." :-) $\endgroup$ – jamesqf Jan 25 '18 at 19:15
  • $\begingroup$ @AngelPray do you have a source/proof for "Changing the color of your sclerae doesn't affect your vision" $\endgroup$ – theonlygusti Jan 25 '18 at 19:37
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    $\begingroup$ The sclera is opaque. Being opaque, it does not transmit light. Light enters the eye through the pupil. This has been known since at least the Renaissance. For example, see the free book Hand-book of Natural Philosphy. Optics by Dionysius Lardner, London, 1856, available on Google Books. $\endgroup$ – AlexP Jan 25 '18 at 19:52
  • $\begingroup$ @AlexP: Also, many animals (I'm tempted to say most, since I can't offhand think of one that does) don't have an easily visible sclera, yet seem to see perfectly well. $\endgroup$ – jamesqf Jan 26 '18 at 4:06
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There is no visual difference

The white you see is, as Frostfyre linked in the comments, down to the sclera. It just a connective tissue that supports the optical parts of the eye.

Social differences

A theory on why the Sclera is white, called the cooperative eye hypothesis suggests the white of the eye is there to provide contrast such that another human looking at you can see where you're looking. This is proposed as a useful method of non-verbal communication, as a warning, an indication of where to go or even just an addition to the already diverse portfolio that makes up body language.

Your black Sclera would remove this teamwork/social advantage.

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  • $\begingroup$ Do you have a source or proof that the world would look identical when viewed from eyes with black sclera. $\endgroup$ – theonlygusti Jan 25 '18 at 19:35
  • $\begingroup$ I also wonder if there isn't some amount of light that penetrates through the sclera into the retina, perhaps providing some input on total light levels. Pigmented sclera would reduce this, which might interfere with (increase) melatonin production or something. Probably insignificant though. $\endgroup$ – Jason K Jan 25 '18 at 19:36
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    $\begingroup$ @theonlygusti There are human diseases that significantly darken the sclera, plus you can get very large scleral contact lenses that are opaque. None of these things appear to affect vision (unless the contact lens has an opening smaller than your iris, which would physically impede vision a bit in low light). $\endgroup$ – Jason K Jan 25 '18 at 19:39
  • $\begingroup$ @theonlygusti Reports on the black sclera without another pre-existing condition effecting things are only found (as far as I could see) when people are talking about contact lenses. Some have complained of tunnel vision but this only seems to be a result of the fact the opaque sclera of the lens is on top of the eye, rather than level with it. So, yes, it doesn't seem to effect anything. On top of that the white of your eye doesn't let any light through so, white or black it shouldn't effect the amount reaching your retina. $\endgroup$ – Lio Elbammalf Jan 25 '18 at 20:11
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    $\begingroup$ dogs also can follow our eyes. $\endgroup$ – user25818 Jan 25 '18 at 21:23
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People cannot know what direction you are looking

As you say, there would be less glare, but it would also mean that it is difficult to distinguish pupils from your sclera.

There is also a precedent; black spider monkeys for example often have black sclera. Or... possibly massive irises that fill the entirety of their visible eye.

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  • $\begingroup$ Do you know why the monkeys evolved the black sclerae. $\endgroup$ – theonlygusti Jan 25 '18 at 19:37
  • $\begingroup$ @theonlygusti I am not aware of any reason for black sclerae adaptation, no. $\endgroup$ – Piomicron Jan 25 '18 at 19:38
  • $\begingroup$ Why could people not know what direction you're looking? That would apply only if the iris was also black, or a very dark brown, and in many people it's not. $\endgroup$ – jamesqf Jan 26 '18 at 4:09
  • $\begingroup$ In just about any animal, including our primate cousins, the colored iris occupies the entirety of the visible eye. Google image "(animal of your choice) eye". Humans are the ones - maybe the only ones - with big rims of white sclera. It has been posited that this helps with sociality: we know where an individual is looking. $\endgroup$ – Willk Jan 26 '18 at 14:13
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Your vision wouldn't change but you would definitely stand out in a crowd as unusual (and creepy) and be very striking if you had bright blue eyes.

It might have a military use as part of camouflage for soldiers (or burglars) sneaking around at night.

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Combining comments from @AlexP, @AngelPray, and myself:

If your sclera naturally started out as black, it would not have any impact on your vision. The sclera is opaque. Being opaque, it does not transmit light. Light enters the eye through the pupil. This has been known since at least the Renaissance. For example, see the free book Hand-book of Natural Philosphy. Optics by Dionysius Lardner, London, 1856, available on Google Books. https://books.google.ro/books?id=9jkDAAAAQAAJ

But this question is about someone changing the color of the sclera with dye. If done right, doing so would not change vision at all —for the reasons described above. But the dye can harm your vision if applied improperly, as reported in one well publicized recent news story: http://www.chicagotribune.com/lifestyles/health/ct-eyeball-tattoo-complications-20171002-story.html

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