|The iris is the blue area. The other structures visible are the pupil center and the white sclera surrounding the iris. The overlying cornea is pictured, but not visible, as it is transparent. Also pictured are the red-colored blood vessels within the sclera. These are easily visible on any person's eyes.|
|Schematic diagram of the human eye. (Iris labeled at upper left.)|
The iris (plural: irides or irises) is a thin, circular structure in the eye. It controls the diameter and size of the pupils and thus the amount of light reaching the retina. Eye colour is the colour of the iris, which in humans may look green, blue, brown, hazel (a combination of light brown, green and gold), grey, violet, or even pink. In response to the amount of light entering the eye, muscles attached to the iris expand or contract the the center of the iris, known as the pupil. The larger the pupil, the more light can enter.