nervous tunic
Today I learned that I have a nervous tunic. Two of them, in fact.
Turns out that nervous tunic and neural tunic are other names for the retina. Most of the online references to nervous tunic as such seem to be in veterinary contexts, so it’s possible that that phrase is used mostly to talk about the eyes of nonhuman animals; but I did see a couple of places that used that term in reference to human retinas. I’m not sure whether there’s a difference in meaning between nervous tunic and neural tunic; I’m guessing that the latter is a more recent synonym for the former, but that’s just a guess.