Structures of the Uveal Tract

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  • 0:00 Grapes & Eyes
  • 0:18 The Uveal Tract
  • 1:22 Iris, Choroid, Ciliary Body
  • 4:09 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

Grapes, blue colors, brown colors, green colors and black colors are all a strange but true part of this lesson on a particular part of your eye, called the uveal tract. What is it? Take a look!

Grapes & Eyes

Do you like grapes? I sure hope so! Because this lesson has to do with the grape of your eye. It really does. You're probably confused as to what in the world I'm talking about. Stay tuned to find out what grapes have to do with your eye as we cover the structures of the uveal tract.

The Uveal Tract

The uveal tract, or simply uvea, is the pigmented middle membrane of the layers that make up the eye. The uveal tract is also called the vascular tunic of the eye because it is rich in its blood supply - i.e., vascular - and because it envelops the eye like a tunic would cover a body. So, to recap, the uvea is pigmented and has a nice supply of blood vessels.

And here is where our grapes come in. Uvea is a term that comes from the Latin for grape, uva. In living tissue, this middle membrane has a reddish-blue color to it, like that of a grape. However, if you were to take an eyeball preserved in formalin and cut it apart so only the uvea remains, it looks blacker in color but still has the appearance of a grape in its size and texture. Cool, huh?

The uvea consists of three main parts:

  1. The iris
  2. The ciliary body
  3. The choroid

Let's define each of them and figure out what they do.

Iris, Choroid, Ciliary Body

Look into the eyes on your screen. Look at how beautiful they are: some are brown eyes, some are green eyes, some are blue eyes. These eye colors are all thanks to the iris, the colorful muscular portion of the uvea that is perforated by the pupil, with the pupil being the black circular opening in the center of the iris that allows for light to enter the eye.

Iris colors

The iris has two important functions. It contracts to make the pupil smaller so less light gets into the eye on a bright sunny day, and it dilates to increase the amount of light entering the eye when in a dark room. So, when you step outside from a dark room and into the bright outdoors and begin to squint in pain from the light, you can be sure your pupils are getting smaller to adjust for this.

Anyways, located right next to the iris is the ciliary body, a thickened part of the eye, located between the iris and choroid, which modifies the shape of the lens and produces the fluid that fills the anterior (front) portion of the eye, called aqueous humor.

The muscles of the ciliary body change the shape of the lens to help us see near or far. The lens is the part of the eye that focuses images on the retina, a structure located at the back of the eye. The retina is a layer of the eye that converts light into an electrochemical signal the body can recognize and interpret as a picture.

Ciliary muscles help us see closer by making the lens thicker, like a magnifying glass. They help us see distant objects by making the lens thinner and flatter, like a window. Just try looking at a distant object through a magnifying glass - kind of hard no? That's why you have ciliary muscles! To adjust the shape of our lens so we can see normally.

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