The function of the iris is to control light levels in the eye. The round, black dot in the center of the iris is called the pupil.
The iris is the barrier between the front and back of the eye. Each iris has a muscle running through it that constricts and dilates to allow the right amount of light to enter the eye at any given time. The sphincter muscle lies around the edge of the pupil. In bright light, this muscle contracts, allowing only a small amount of light to get it. In dim light, the sphincter muscle dilates, letting in as much light as possible.
Each person's texture, color and pattern of the iris is unique and the color of the irises come from a pigment called melanin. Eye color comes from the amount of melanin a person produces in black/brown or red/yellow combinations.
Like other parts of the body, the iris may become diseased or infected. When the iris becomes inflamed, the result may be blurred vision and light sensitivity. Iridocyclitis is a condition in which the iris requires antibiotics to function normally. Congenital problems of the iris such as, iris coloboma and aniridia are rare and require seeking professional medical treatment.