The human eye functions much like a digital camera. It gathers, focuses, and transmits light through a lens to create an image of the surrounding environment.
In order to see, there must be light. Light enters the eye through the
cornea, the clear front surface of the eye. The
iris of the eye functions like the diaphragm of a camera, controlling the amount of light entering the eye by automatically adjusting the size of the
pupil, which acts like an aperture. In dark conditions, the pupil widens, while in bright conditions, the pupil constricts.
The eye's crystalline
lens, located directly behind the pupil, helps to focus the image on a light sensitive screen, called
retina. The image formed on the retina is upside down. The
optic nerve transmits signals to the visual cortex in the brain, which flips the image so that we are able to see an erect image. This is how the human eye works.