Could an animal have eyes like a reflecting telescope, rather than with a lens? The back of the eyeball is a paraboloid mirror, and the retina is a small body on its focal plane.

Because the retina must be small, such an eye would have poorer resolution than a vertebrate eye of similar size.

Are there any organic mirrors in the real world? How smooth is the reflective layer behind a cat’s retina?

Perhaps I’ll inflict this idea on worldbuilding.stackexchange.com – in the form of a question, though I dislike Jeopardy for that gimmick.