Looking for a movie about mutants in a cave?

Summary: People are trapped in a cave (or some sort of trapped area), forced to inbreed to survive, and become mutants without eyes. They have very keen hearing and smell and other senses. The film takes place when someone explores (somehow gets in?) the cave. I think it is shot from a handheld camera, but I'm not sure. Does anyone know what the film is called? I've been looking for it for ages!