"To suppose that the eye with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic abberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest sense."
Origin of the Species
And speaking of eyes, here is an optical illusion to wig your eyes out with. When you look directly at a wheel it doesn't move but letting your eyes rove around the picture makes it all seem to come alive. Optical illusions are so weird.