My attempt at explaining why EMS works and why swapping eyes won't help
Ok it always bothered me bc like there's no way it'd cure myopia just by swapping eyes so I decided to try to understand it. And yeah i reject swapping eyes bc that wasn't the point of EMS in canon, it was meant to be a sacrifice and a tragedy.
As we know, Mangekyo Sharingan (MS) has 2 problems: bad eyesight when not using sharingan and painful eye bleeding.
I hc that MS bleeds so much, bc in order to activate it, the user pushes much more chakra into their eyes and it creates very high blood pressure there. Pushing so much chakra into his eyes also worsens the cornea which affects the vision. They basically speedrun myopia.
For EMS to work they take not the whole eye, but only donor's eye's cornea, iris and anterior chamber, where by my hcs are chakra channels for the sharingan. Uchiha's eyes are stuffed with chakra channels. Same with Hyuuga, its went down from Otsutsuki's eyes.
So they take this (marked with yellow) part and basically slap onto the old eye, basically fusing these two areas. It somehow works, cuz in no way that would work for any normal human. But they're shinobi and Uchiha, who are direct descendants of an alien princess, that's already not really normal human.
Ok so, how then this procedure really works? Basically, with fused cornea it solves the problems
- Fixes myopia. Like check out how lasik works, its pretty similar.
- Eye bleeding. New cornea gives the old eye more chakra channels and it helps to redistribute the strain of the chakra pressure enough for the eye not to strain so much so no bleeding.
- Adds new powers because of some chakra that was left in the anterior chamber + new cool MS pattern bc it's basically iris on iris situation.
Oh and btw, i think its pretty obvious why it should be siblings, mostly bc it's way less of a chance for transplant to get rejected.