#Blindspot
Each eye has one. They check it when people get their eyes examined. When I was 17 an ophthalmologist told me one of mine was "extended", and that it might be due to a brain tumor. He told me to come back in 2 weeks. When I did, he retested and decided that it was something I was born with and I didn't have a tumor. I think he had to look it up in a book or something, he wasn't a good doctor. A few years later he died of AIDS.