There are many ways to break an eye, and evolution has explored them all. Lenses have degenerated. Visual pigments have disappeared. Eyeballs have sunk beneath the skin or been covered by it. One species alone, the Mexican cavefish, has lost its eyes several times over, as different sighted populations moved from bright rivers to dark caves and independently abandoned vision. As Eric Warrant tells me, “Why Gollum in The Hobbit had extra-big eyes makes no scientific sense.”
