SAP - The Eye Lesson
The Eye
How does the eye work? In the diagram below, you can click on each word to read about the function of that part of the eye.
Learn about the parts of the eye in the activity below:
It's a combination of rods and cones in your eye, plus some color receptors in your occipital lobe that enable color vision. Two theories explain these processes.
- Trichromatic Theory
- Opponent Process Theory
Trichromatic Theory explains that there are three types of cones in the retina: ones that specialize in seeing either red, green, or blue. Humans can see other colors through the stimulation of a combination of these cones.
Many people who are colorblind are missing one or more of these types of cones.
But trichromatic theory cannot explain why people see afterimages. To experience an afterimage, stare at the image below for 20-30 seconds and then look at the white square. For a moment, you should see a reversed image.
Opponent Process Theory explains these afterimages. When the brain begins the process of interpreting the incoming visual information, it uses sensory receptors that come in pairs. The pairs are red/green, blue/yellow, and black/white. When one of the pair colors is activated, the other is inhibited. And so for a moment when you look away from that color, the one that had been firing takes a rest and the other fires. Look at the images again and notice that you see the other color of the pair each time you look away.
How many people do you know who have to wear contacts or glasses to be able to see well?
In a perfectly functioning eye, vision can focus on objects close up and far away. But some people are either far sighted or near sighted. Farsightedness and nearsightedness are caused by a lens that doesn't accommodate correctly to focus an image on the retina. Sometimes the lens is the wrong shape or the eye is the wrong shape, but either way the resulting lack of clear vision is the effect.
You may have noticed that your parents or grandparents hold the menu at arms' length to read it when you're at a restaurant and they've forgotten their reading glasses. As we age, our lenses become less able to change shape, so we lose the ability to focus on items close to us.
Farsightedness is a normal side effect of aging, but other visual problems can be caused by lifestyle or environmental issues. These include UV damage from not wearing sunglasses, head trauma that leads to eye or brain damage, untreated STD's like syphilis or chlamydia, and vitamin A deficiency from a poor diet, amidst other issues.
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