The eye works as follows:  Light enters the eye through the cornea. The cornea, being a refractive medium, bends the light entering the eye, which then passes through the pupil and enters the lens. Once the light enters the lens, the lens adjusts the focal length based on the distance to the object. The image is formed on the back of the eye at the retina. The signal is picked up by special cells, which use different pigments. Each pigment reacts differently to a different photon frequency. The signal is transmitted to the brain as an electrical impulse via the optic nerve.