Bats aren't blind. They're not even a little nearsighted. What they do have is exceptionally acute hearing. They also possess sonar so sophisticated, it tops that used by the U.S. military [source:Science Daily]. This sonar, or echolocation ability, involves the bats producing ultrasonic pulses, or sounds, which then reflect off objects. The bats process the reflected sound to avoid obstacles, to effectively hunt and to properly orient themselves.
Since bats are nocturnal animals, and have such amazing echolocation skills, their sense of sight isn't that important. Perhaps this is why the myth about their blindness arose. It also may have something to do with the fact that bats, the world's only flying mammals, have long been viewed by humans as both fascinating and repulsive -- qualities that have led to many myths about the creatures.