You gotta believe...

......that in some cases, people who experience some vision loss see objects and people who aren't really there.  Since the optic nerve is part of the brain, and nature abhors a vacuum, the brain fills in the "blind spots" with some stored visual memory.  Thus you can see things and even people who are invisible to others.  You're in trouble, though, if you hear their voices.  (That might explain the mouse running across the kitchen floor.)