What is the Iris of the Eye?

What is the Iris of the Eye?

The iris is the most noticeable part of the eye: the pigmented, circular portion. It is the part that makes your eye blue, brown, green or hazel and is caused by the amount of pigment melanin that is present. Melanin is also the pigment that gives color to our skin and hair. 

The iris lies in front of the crystalline lens and separates the anterior chamber from the posterior chamber. The iris surrounds the pupil, which is just empty space that allows light to pass thru. It controls the amount of light that enters your eye by changing size. For example, when you are in a bright environment your iris will stretch out, causing the pupil to shrink (constrict) and limit the light that passes. When the environment is dark, your iris will shrink, causing the pupil to enlarge (dilate) allowing more light to pass. 

The iris is made up of tissue and smooth muscle fibers. It is these tissues and muscles that cause it to expand and contract. The sphincter pupillae surrounds the border of the pupil and controls the iris contracting in size. The muscle that causes the iris to expand is called the dilator pupillae.

There are many conditions that can affect the iris of the eye:

  • Iritis is an inflammation of the iris.
  • Aniridia is a genetic defect in which the person is born without part or all of an iris.
  • Coloboma is a large hole in the iris
  • Synechiae is adhesions that occur between the lens and the iris

To learn more about the iris or other components of the eye, contact Snowy Range Vision Center by calling 307-742-2020 or visiting website


Snowy Range Vision Center

405 South 30th Street
Laramie, Wyoming 82070

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