Copper in the Cornea

The cornea is supposed to be clear and avascular. So how did the copper get there if this is a bloodborne problem? One clue is that pathological studies of the eyes of patients with Wilson disease found increased copper in the aqueous humor. But one thing that didn't quite make sense to me initially was why do you get a ring shape? Why doesn't the whole cornea end up discolored by this copper? Right? Like, why is it just the periphery?"