" ...Someone can intentionally fake blindness for some secondary gain (malingering)--a prisoner who says he can't see in order to try to avoid going directly to jail. It is not difficult to figure out when patients say they are blind but can actually see. We have a simple test that lets us determine whether the eyes are functioning. Using a rotating striped drum, we test for something called optokinetic nystagmus. as the drum spins, normal eyes will be seen moving back and forth.

If a striped rotating drum is not available, you can always use a picture of J. Lo's rear. Move it back and forth, and any normal eyes will follow. "

― Mark Leyner , Why Do Men Have Nipples?: Hundreds of Questions You'd Only Ask a Doctor After Your Third Martini