Pigmented Area of the Eye

The pigmented area of the eye is the iris. The most noticeable iris features are its color and its center hole, or pupil, through which light enters the eye. The iris adjusts pupil size to regulate the amount of light entering the eye.

Iris Function

• The iris regulates pupil size using two sets of circular smooth muscles. Exposure to bright light causes the pupillary sphincter muscle around the pupil's perimeter to contract and shrink the aperture. When light is dim, dilator muscles running radially through the iris, like spokes on a bicycle wheel, enlarge the pupil, according to California State University Long Beach.

Eye Color

• Melanin pigments, produced by cells called melanocytes within the iris, produce eye color. Eumelanin consists of black-brown pigments and pheomelanin of red-yellow pigments. The amount and distribution of each pigment in the iris determines eye color, says the University of Utah Eye Center.

Iris Color Changes

• According to Dr. Larry Bickford, a practicing optometrist in Santa Barbara, California, babies are born with "neutral" eye color. Only after the eyes are exposed to sunlight do the melanocytes produce the pigments responsible for eye color. Eye color may also change somewhat when adjustments in pupil size either compress color pigments or allow them to spread out.