美国英语听力80篇2 Lesson36
ColorMax Lenses
Some people cannot see all colors correctly.
They cannot see all the colors in a rainbow or a sunset.
They cannot tell if the meat they are cooking is done or if a fruit is ready to be eaten.
Poor color sight also prevents people from holding jobs such as policeman, pilot, and cook, and from serving in the military.
Last year,the first eyeglasses were approved in the United States to treat people with poor color sight.
They are called ColorMax glasses.
However, the Food and Drug Administration warns that the new glasses do not give a person normal color vision.
The glasses permit a person to better see differences in colors that used to look the same to them.
About 250,000,000 people around the world have a condition limiting the colors they see.
The condition commonly is known as color-blindness.
Color-blindness can result from injury to the eye, medicine, or age.
However, most people are born with the condition.
Genetic colorblindness is caused by a defect in the retina, the inner wall of the eyeball.
The retina contains cones and rods, two kinds of cells that react to light.
Cones permit us to see color and to see in bright light. Rods sense brightness and darkness.
A normal eye has three cones. One cone is sensitive to blue light, one to green light,and another to red light.
Most colors are a mixture of the three colors.
Usually when a person sees an object, all three cones become active.
The brain then uses this information to decide the color.
A normal eye can see about 200 colors.
People with poor color sight have damaged or missing cones.
They may see the world in as few as five colors.
The most common type of color-blindness is the failure to see reds or greens.
The ColorMax glasses improve color sight by changing the wavelength of light entering the eye.
They do so by covering the glass with a colored lens that blocks out light.
For example, a red lens lets in red light but blocks out most blues and greens.
Green light seen through red lenses will appear darker because light from it is not reaching the eye.
The glasses make colors brighter and darker so that the differences are easier to see.
People say ColorMax glasses help them see an increased number of colors
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