How The Eye Works
A camera is often compared to the eye. With a camera a series of lenses bring an object to focus on the film located inside the camera body. The eye, like the camera, bring an object to focus on the retina.
The clear cornea is the first thing the light of an object encounters, which bends (refracts) the light. The light then passes through the pupil whose size is adjusted by the iris depending on the lighting conditions. The light (from the object) continues through the crystalline lens of the eye, where it is further focused to the retina. The retina, being compared to the film in the camera, is the light sensitive lining of the eye. As light strikes the retina layer the specialized cells within are stimulated, which in turn sends signals to the back of the brain (to the visual cortex) via the optic nerve.