I'm routinely impressed that my cat uses a litter box with no problem that is almost completely dark at night. Not sure how she can see what she's doing, but it's cool!
I don't think she needs to see anything (although she probably does, at least dimly). Even humans should have no problem navigating around a familiar environment without relying on vision -- especially those humans accustomed to it, such as blind people. And cats get plenty of help from their other senses that are considerably keener than their human equivalents.
