Eye anatomy. Cutaway illustration showing the internal structure and anatomy of a human eye. The front of the eye is at right. Light entering the eye passes through the pupil, a hole surrounded by the iris (coloured) 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 in the retina that are transmitted by the optic nerve to the brain. The optic nerve and blood vessels enter and leave through the back of the eye. Eye layers shown here include the conjunctiva, sclera, and choroid.