John in Kansa, Eliza, there was a lovely fiction children's story in one of the readers I used to teach. It was about a milkman who gradually became blind but was able to keep working because his horse knew where to stop. I can't remember its title, nor can I remember if there was any explanation about what the milkman did if a customer left a note changing the order. Maybe he was supposed to be illiterate and had always shown the notes to someone else to read. I've always imagined that he was supposed to know where everything was stored in the wagon, how many steps from the road each house was, etc. I think the story ended with the horse being too old to work and the milkman then having to retire. None of his employers or coworkers were supposed to have realized he was blind until then.