How was the science behind vision discovered?

[pluto2]

Before the invention of the mirror and before the science of vision was discovered, how did ancient humans know that they had eyes that could sense light?

 

[btr]

That eyes were the organs for vision would have been obvious; if you cover your eyes, you can't see, for example. The notion of "light" would probably have arisen somewhat later, perhaps as a consequence of observing shadows.

Ideas about the relationship between light and vision, and the actual nature of light, developed quite gradually. The Wikipedia article on light has a section on the history, which gives a good overview:

http://en.wikipedia.org/wiki/Light#Historical_theories_about_light.2C_in_chronological_order