Writing Hua Cheng/monocular vision

(posted originally on tumblr, sticking it here too for posterity)

First off, while I may be extremely nearsighted, I do have full binocular vision, and I am not a medical professional, none of this is medical advice, etc. That said - I have spent a lot of time both cosplaying and writing one-eyed characters because... somehow I keep ending up in these fandoms? idk I'm gonna blame CLAMP for this one, they started it. And I am a research fiend, so, here’s some basics at least.

Hua Cheng-specific stuff:
- Given that Hua Cheng keeps his right eye covered in life, even as a child, I think it's safe to say that even if he could have had normal vision in it (ie, the only thing off with it is the color), he doesn't actually - if there's vision impairment in one eye at a very young age, the brain doesn't develop the neural pathways for controlling it and interpreting information form it, and that can persist even after vision correction without other intervention ('lazy eye', amblyopia)
- I would assume that even in forms with two eyes, he can still only see out of the left one, as that's what he's used to/has lived experience of - can't create what you don't know, after all (plus whatever is up with the right-eye magic vision)
- Given he's spent his whole life (and unlife) with monocular vision, pretty much every accommodating habit will probably be extremely ingrained at this point, not stuff he really has to think about.

More general stuff:
- Contrary to what a lot of people think, you actually only use binocular vision for close-up depth perception. Beyond three or four feet, the brain uses other cues - perspective, lighting, parallax motion - to determine distance. Consequently, one-eyed people with normal (or correctable-to-normal) vision in their remaining eye can usually hold driver's licenses (there are almost certainly regional exceptions to this, but on the whole, yes)
- On the flipside, that close-up depth perception is more important for everyday things than you might realize - pouring drinks, cutting up food, etc. Physical touch is the quickest compensation there - if the spout of the teapot is actually touching the rim of the cup, you can be certain you are going to pour into the cup and not onto the table an inch in front of the cup.
- More head movement to make up the missing visual field - particularly for stuff like driving where spatial awareness is very important (and presumably like... fighting too, but perhaps unsurprisingly this is not talked about in most modern resources and I have not tested it)
- Walking into things isn't really much of a problem - if it's in front of you, you generally have enough lead-up where it's in your field of vision to avoid it. It's easy to miss stuff off to the bad side, though, and easier to be startled by unexpected movement on that side as well.
- Maybe obvious, but it's easier to hold conversations with people on the side you can see, instead of having to twist your neck to look at them
- Eyestrain is an issue! And in general if you're down to one eye you wanna take extra-good care of it.

And a real solid general resource for questions of 'how do you do [x] with only one eye' is A Singular View by Frank B Brady - Archive.org has a digital copy of one of the early editions available to borrow here, or your local public or university library system may have a more recent edition.