Would you be able to see anything without a lens in your eye? Does the lens change shape? Does the iris? What structure gives you your eye color? Find out all of this and about things like the ciliary muscles and the cornea as we delve into this lesson.
Structures at the Front of Your Eye
When you're watching your favorite show on TV, there are a lot of very important structures involved in helping you see and interpret the light entering your eye from the television. As the light leaves the television, it travels through the air to reach several major structures in the very front of your eye, before the light even reaches the critical structures at the very back of your eye. These important structures at the front of your eye include the cornea, iris, pupil, lens, and the ciliary muscles.
We'll find out how all of these structures work together to help you watch your favorite shows on TV.
The cornea is the outermost layer of the eye
As the light leaves the television, the very first important structure involved in eyesight that the light hits is known as the cornea. The cornea is a transparent layer, at the very front of your eye, which covers the iris and the pupil. We'll get to what the iris and pupil are in just a second.
What's important to know about the cornea is the fact that it's not just important in vision through its ability to bend light as it enters your eye. The cornea is also involved in sensing pain if something like an evil cat scratches your eye or an eyelash keeps irritating it.
In addition, if someone were to gently poke your eye somewhere away from the cornea, you could keep your eye open if you try really hard. However, if someone were to poke your cornea, you would be forced to close your eyelids through an involuntary reflex. Please, do not try this at home! The cornea is easily scratched, and because of all the nerves located there, a scratched cornea is very painful!
The Iris and Pupil
Hopefully, you never have to experience an ugly cat scratch of your cornea. In fact, I hope that instead of that ugliness, people have complemented you on how beautiful your eyes are. When saying this, they were most likely referencing the fact that you have beautiful irides, which is the plural form of the word iris. Your iris is the structure that gives you your eye color and controls the amount of light reaching the back of your eye.
The iris controls the amount of light entering the eye
Take a look in the mirror. Take a really close look. What color are your eyes? They can be brown, blue, grey, green, or a combination of all those. That color, that beauty, comes from the iris.
Also note that there is a black hole in the middle of your iris. Don't worry; unlike black holes in outer space, it isn't dangerous and won't rip you apart. That black hole is known as the pupil. It is nothing more than a hole in the middle of the iris that allows light to enter inside the eye.
The pupil changes diameter as the iris contracts or expands thanks to little muscles that encircle the iris. When a lot of light enters the eye, such as on a bright sunny day, the pupil will constrict. If there's not enough light entering the eye, like when you're in a dark room, the pupil will dilate to let more light in.
The Lens and Ciliary Muscles
As the light enters through the cornea and then through the pupil, it will hit a really important structure known as the lens. The lens is a structure located behind the iris and focuses light rays entering through the pupil in order to form an image at the back of an eye. Basically, the lens helps to focus light so you can see things near to you, like the computer screen, and far away, like the birds flying up in the sky outside your window.
The lens is able to achieve the process of focusing on objects near and far away, known as accommodation, through muscles that attach to the lens, called ciliary muscles. As the ciliary muscles contract, the lens will become shaped more like a ball than a disc. This will allow you to focus in on objects close to your eyes, like the text in a book. As you decide you're done reading and would rather stare at the birds outside, the ciliary muscle will relax, and the shape of the lens will change into the shape of a flat disk; this will allow you to focus in on objects far away.
The lens focuses light, which creates images in the back of the eye
Here's an interesting fact: if you didn't have a lens, you'd still be able to see. However, you'd only be able to see things located at a very far distance. In simple terms, the lens is necessary to help you see things close to you as opposed to far away.
Let's go back to watching TV instead of birds as we review the important things in this lesson. As light leaves the TV, it will first go through your cornea, which is a transparent layer, at the very front of your eye, that covers the iris and the pupil. The light will then move through the pupil, which is nothing more than a hole in the middle of the iris that allows light to enter inside the eye. If you recall, the iris is the structure that gives you your eye color and controls the amount of light reaching the back of the eye.
As the light passes through the pupil, which is a hole formed by the iris, it will reach the lens. The lens is a structure located behind the iris and focuses light rays entering through the pupil in order to form an image at the back of an eye. This focus is achieved through the contraction or relaxation of muscles that attach to the lens, called ciliary muscles. After passing through all of those structures, the light will continue on to much smaller but equally important structures involved in your eyesight located in the back of the eye.
At the end of this video, you will be able to:
- Describe the function of the cornea, pupil, iris, lens and ciliary muscles
- Explain how light travels through the eyes