Your eyes allow you to see the world around you. But have you ever wondered how they work?
First, it’s important to know that vision depends on your brain as much as on your eyes.
Your eyes’ main job is to detect patterns of light. Then, they work with your brain
to turn those patterns into images. Let’s take a closer look…
Light rays bounce off an object you are looking at. Let’s say the object is a dog. The light
reflects off the dog to your eye.
Then, the light enters through the outer part of your eye, called the cornea. The cornea
is clear like a window. It helps your eye focus the light to make things look sharp
and clear.
Next, the light rays pass through an opening called the pupil. The pupil is the dark round
circle in the colored part of your eye. The colored part is called the iris. It controls
how wide the pupil is and how much light can pass into your eye.
In bright light, the iris narrows the pupil, reducing the amount of light that enters the
eye. In dim light, the iris widens the pupil to let in more light. All of this happens
automatically.
Behind the iris is the lens of the eye. It helps focus the light coming into your eye
so you can see things clearly. The lens flattens so you can see things that are far away and
bends so you can see things up close.
When the lens, cornea and pupil are all working together properly, they will focus light on
the back of the eye. That’s important...because lining the back of the eye is the retina.
There are about 130 million tiny cells in the retina that are sensitive to light. When
these cells detect light, they turn it into electrical signals. Those signals eventually
make their way through the optic nerve — which is like a cable connecting the retina to the
brain.
The retina helps create a rough image, but it sees the world upside down. It’s your
brain that turns what you see right side up.
Also, when you look at an object, each eye gets a slightly different view of the world.
The brain combines those views and makes them into one picture. The brain also adds a lot
of details to your vision, so that you can see complex shapes, movement, depth, and a
rainbow of colors.] And of course, the brain connects your sense of sight to things you
already know…so that when you see a dog, you recognize it as a dog, and not a cat or
a monkey!
And that’s how you’re able to see! To learn more about how your eyes work, visit nei.nih.gov/kids