In this particular episode of Ask an Eye Doc, you will learn:

  • What the iris is
  • What the iris does
  • What the pupil is
  • Iris muscles
  • What is dilation
  • A cool pupil trick

If you have other questions about the cornea or any other eye anatomy question, click Ask a Question to be featured on Ask an Eye Doc!

For you readers out there, here’s the answer in written form:

Today’s question is a simple anatomy question regarding what is the iris. Anatomy means the structure of the body.  So today we’re going to learn about the iris, which is a basic structure on the front part of the eye. Knowing about the iris is useful for referencing other structures in the eye and understanding other eye topics such as eye pressure, glaucoma, and dilation.

What is the iris?

The iris is the color part of your eye. It sits right behind the cornea and is generally flat. It controls the amount of light that enters your eye by adjusting the size of the pupil, which the dark opening found in the center of the iris.

Iris muscles

Pupil size is controlled by two iris muscles that pull in opposite directions: radially & circularly. The radial muscles of the iris are lined up like spokes on a bike. When they contract, they become shorter in length, which increases the size of the pupil. This is called dilation.

When the circular muscles of the iris contract, they cinch the pupil, like tightening your belt. This decreases the pupil size and reduces the amount of light that enters the eye.

Your pupil size is constantly changing, depending on where you are focusing and how much light is around. For example, pupil dilation happens naturally in dark conditions and when looking far way, and pupil constriction happens in bright conditions and when you look at something up close.

Cool pupil trick

If you want to see a cool trick, step into a dark room with a mirror and turn the light off. Now turn the light on and watch what happens to your pupils. When the light is off, your pupils automatically dilate due to the lack of light. This is the body’s way of getting as much light as possible inside the eyes when there’s not much around. When the light turns on, your eyes don’t need as much light, so the pupils constrict.

So now you know what the iris is!

If you have another question about the iris or any other eye anatomy question, click Ask a Question to be featured on Ask an Eye Doc.



AAED 19: What is the iris?
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