Eye anatomy. Computer artwork of a section through a human eye, showing its internal anatomy and structure. The front of the eye is at right. Light entering the eye passes through the pupil (black), a hole surrounded by the iris (blue) that controls its size. The light then passes through the lens (grey) and is focused on the retina, a light-sensitive layer rich in blood vessels lining the rear and inside of the eye. The light triggers signals that are passed through the optic nerve (yellow) to the brain, where they are interpreted to provide vision. The inside of the eye is filled with a clear gel, the vitreous humour. At top and bottom are the eye muscles (muscles of the orbit.