Bats Are Blind
"The belief, reflected in the phrase 'blind as a bat,' that bats cannot see and rely entirely on hearing to get around."
Every bat species studied has fully functional eyes, complete with a working retina, lens, and optic nerve, and many bats are believed to see more sharply in low light than humans do. The confusion comes from echolocation, the genuinely remarkable biological sonar many bats use to track fast-moving prey in complete darkness, which is so effective that people assumed it must be compensating for blindness rather than working alongside functioning eyes. In practice, the two senses divide the labour: vision tends to handle long-range navigation, spotting the horizon, and watching for predators, while echolocation takes over for the fine, split-second work of chasing insects in the dark.