#science stuff

Yes, bones do secrete hormones, including osteocalcin, which plays a role in the fight or flight response. When the brain detects danger, it signals the skeleton to release osteocalcin, which helps to activate the sympathetic nervous system and suppress the parasympathetic nervous system, enabling the body to respond to the stress. 

photos of Elena - reactor 4's 2000 ton upper biological shield - post explosion

⚡ ~ Plasma ~ ⚡ (Rihard-Clement-Ciprian Diac)

H20 - very good please drink water

Add an oxygen molecule. Now this substance can kill you

If 32 mols of propane are turned purple, how many bricks will Timmy have to shove in the toilet at stp?

Where am I go with this? Tobirama's eyes are red, not blue. The Uchiha do cooky chakra things with their sharingan so ignore them. Tobirama's pupils are often drawn as red too. Therefore I sometimes like to headcanon that Tobirama has excellent pheripheral vision but he's basically blind in his central vision. It sucks because pheripheral vision is mostly just for stuff like detecting movement and spatial awareness while central vision is used for sharp details like being able to read or differetiate color. It sounds like a disability made up for a fantasy world but I did go temporarily blind like this so it can happen.

When you try focusing on something your eyes automatically use your central vision to do so but since you don't have central vision whatever you're focusing on disappears. Potentially Tobirama can look an Uchiha directly in the sharingan and not fall victim to a genjutsu because he simply can't see the sharingan. Downside is is that he does fuinjutsu so just imagine him just blankly staring at a wall, not even looking at the seal he's making. I don't know if glasses to fix this exist becuase they didn't when it happened to me so Tobirama's just stuck with such crappy vision that not even glasses can fix it.

Also, this might be a common type of blindness for the Uchiha clan. With how much they stare at stuff, the heat from their katons along with the high brightness from their katons they may as well be staring at the sun. (I did not got blind from staring at the sun).

I am sleep deprived and it's been a long day so hopefully this is coherent. My apologies if it is not.

That's an interesting headcanon. I usually explain to myself Tobirama's red eyes with albinism. I know that it doesn't technically cause red eyes, that most will appear light blue/gray, so it may be a bit of a stretch.

You are right that the eyes' blue colour do not come from any present pigment in the irises, but a phenomenon called Rayleigh scattering which is especially effective at short wavelengths on some molecules because of the resonance of said molecules (for a small reminder, the shortest wavelength on the visible light spectrum is purple/blue, even shorter but not visible would ultra-violet, same for the other end of the visible light spectrum, the longest wavelength being red, and longer but invisible to us being infrared. Sorry, this is basic, but I wanted to get this straight)

It's the same phenomenon that makes the sky blue, this scattering of light on the molecule of the atmosphere making it blue, and the red hues appear when the sun gets lower and reaches the horizon light because the Rayleigh scattering happens longer and the blue light emitted by the molecules (yes it's the molecules that are in resonance that emit a certain colour) will be driven away, leaving the longer wavelengths for us to see, like red or orange (hope I'm making sense)

In any case... it's not really related to vision quality. I think your headcanon is really cool (ignore the anime where Tobirama closes his eyes after locking them with Izuna's) and absolutely hilarious when it comes to the fact that Tobirama seems to look straight ahead when he's working on his seals because he uses his lower peripheral vision (does that mean he has a black spot in the middle of his field of vision, I wonder if his brain fills up some gaps if so, or maybe it's just blurry af, idk)

Sight is linked to two things mainly, though. The retina, and optic nerves. Albinism can cause the nerves to be different, which causes partial blindness to a lot of them, also, the lack of protection from the sun can makes their retina more vulnerable. The fact that their eyes can appear red is actually unrelated, it's just that, contrary to regular blue eyes that have some melanin, theirs have so little if not at all, be can see the blood vessels sightly through, making their eyes appear reddish/purplish. This is why I go with that to explain (realistically) Tobirama's eye colour.

As for the Uchiha, the fact that they burn their retina from staring at their katon is something I hadn't thought about before, but it definitely happens (makes me wanna draw Izuna with sunglasses on the battlefield for protection, even though it a complete anachronism)

You know what, doodle time:

Izuna is a diva even on the battlefield, what more can I say.

Izuna has to be alive for this scene to happen, if not, Madara wouldn't care. Hashirama doesn't know how to explain Tobirama's condition in simple terms (medical nerd)

All of that aside, I find it funny how these asks are now really just people asking for my thoughts/sharing their thoughts about the science and anatomy of the founders.

I don't mind at all, I love science (if you couldn't tell) though I think you should always double check what I say. I'm just a silly fox who likes to draw, I'm still young and definitely have a lot to learn still.