The Visual System: How Your Eyes Work


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

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