Retina

The light sensitive part of the back of the eye that corresponds to the film in a camera.
Just like the film in a camera, the retina captures images upside down and backwards and sends them to the brain for interpretation.
The retina consists of ten layers of neural tissue that is actually considered an extension of the brain.
The center of the retina called the macula, an oval stucture of about 1.5 mm diameter. In the center of the macula is a small "pit" called the fovea. The fovea contains the most sensitive portion of our vision. It is responsible for all fine detail that we see.
For a more detailed explanation see http://en.wikipedia.org/wiki/Retina#Diagnosis_and_treatment