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Vision and the Eye

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Vision and the Eye
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Did you ever hear the proverb, “the eyes are the windows to the soul”? While it’s true that our eyes often express what we are thinking or feeling, they are windows in another sense as well. Like windows made of glass, the eyes let light in and allow us to see.

How well can you see in the dark?

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How We See

The ability to see is called  vision . This ability depends on more than healthy eyes. It also depends on certain parts of the brain, because the brain and eyes work together to allow us to see. The eyes collect and focus visible light. The lens and other structures of the eye work together to focus an image on the retina. The image is upside-down and reduced in size, as you can see in the  Figure   below . Cells in the retina change the image to electrical signals that travel to the brain through the optic nerve. The brain interprets the electrical signals as shape, color, and brightness. It also interprets the image as though it were right-side up. The brain does this automatically, so what we see always appears right-side up. The brain also interprets what we are seeing.

Signal transmission from eyes to brain

Light and Vision

Except for objects that give off their own light, we don’t see things just because light strikes them. We see things because light strikes them and then reflects, or bounces back, from their surface. What we see is the reflected light.

Some things reflect all the light that strikes them. These things appear white. Some things do not reflect any light. Instead, they absorb all the light that strikes them. These things appear black. Other things reflect just one wavelength of light. Whatever wavelength they reflect is the color we see. For example, beads that reflect only red light look red to us.

Summary

  • The human eye is an organ that is specialized to collect light and focus images. Light enters through transparent structures at the front of the eye. It is focused by the cornea and lens on the retina at the back of the eye.
  • The ability to see is called vision. The brain and eyes work together to allow us to see. The eyes collect and focus visible light and change it to electrical signals that travel to the brain. The brain interprets the signals and “tells” us what we are seeing.

Vocabulary

  • vision : Ability to sense visible light and see.

Review

  1. Create a flowchart to summarize how the eye gathers and focuses light.
  2. Explain the meaning of the following sentence:  The eyes sense light but the brain sees.

Missouri Standard(s): 1.2.A.g

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