I guess they're referring to the brain (and, by extension, the eyes!) being an "immunoprivileged zone" [1]... the brain-blood-barrier makes a lot of "everyday"

I guess they're referring to the brain (and, by extension, the eyes!) being an "immunoprivileged zone" [1]... the brain-blood-barrier makes a lot of "everyday" stuff for the rest of the body pretty complex affairs for everything CNS related. [1] https://en.wikipedia.org/wiki/Immune_privilege https://en.wikipedia.org/wiki/Immune_privilege