The eye is an organ of vision and light perception. In the human eye, the iris diaphragm regulates the size of the pupil, allowing more or less light to enter the eye as necessary. Light is focused by the combined action of the curved cornea, internal fluids, and lens. When light reaches the retina, located at the back of the eye, the light-sensitive rod and cone cells are stimulated. They, in turn, send signals to the brain via the optic nerve. How do the rods and cones differ in function? Discuss
Source: The Free Dictionary