Abstract: having 20 / 20 vision means that when you stand 20 feet away from the vision chart, you can see what “normal” people can see at this distance., Normally, the eye can accurately focus the image on the retina. If it cannot focus accurately, myopia and hyperopia will occur., Myopia, if you suffer from myopia, you can only see the near objects, but can’t see the far objects. Then the light will focus in front of the retina. This is because the eyeball is too long or the focusing ability of the lens system is too strong. Myopia can be corrected by concave lenses., Hyperopia, if you suffer from hyperopia, you can only see distant objects, but not near objects. The light is focused behind the retina. This is because the eyeball is too short or the focusing ability of the lens system is too weak. Hyperopia can be corrected by a convex lens., Do you have eyesight? ” width=”400″ height=”300″ src=”//img. jianke. com/article/201510/20151012170511292. Jpg “/ >, 20 / 20” normal “vision. In the United States,” 20 / 20 “is a common expression, and there is even a TV program named after it.,
normally, the eye can accurately focus the image on the retina. If it cannot focus accurately, myopia and hyperopia will occur.
myopia
if you suffer from myopia, you can only see the near objects, but not the far objects. Then the light will focus in front of the retina. This is because the eyeball is too long or the focusing ability of the lens system is too strong. Myopia can be corrected by concave lens.
hyperopia
if you have hyperopia, you can only see distant objects, but not near objects. The light is focused behind the retina. This is because the eyeball is too short or the focusing ability of the lens system is too weak. Hyperopia can be corrected by a convex lens.
vision? ” width=”400″ height=”300″ src=”//img. jianke. com/article/201510/20151012170511292. Jpg “/ >
20 / 20″ normal “vision
in the United States,” 20 / 20 “is a common expression, and there is even a TV program named after it.
through the observation of a large number of people, ophthalmologists have mastered what the “normal” vision should be able to see on the vision chart at 20 feet. Having 20 / 20 vision means that when you stand 20 feet away from the vision chart, you can see what “normal” people can see at this distance. (in metric terms, the standard is 6 meters, so it is also called 6 / 6 vision.) in other words, when your vision is 20 / 20, it means that your vision is “normal” and you can see what most people can see 20 feet away.
If your eyesight is 20 / 40, it means that what your normal eyesight can see 40 feet away from the eyesight chart, you can see only 20 feet away. In other words, “normal” people see exactly the same things 40 feet from the eye chart and 20 feet from you. 20 / 100 means that you still need to be 20 feet away from what your normal vision can see 100 feet from the chart. In the United States, vision less than 20 / 200 can be regarded as blindness.
and
also have vision higher than normal standards. People with vision of 20 / 10 can only see what they see 20 feet away from the vision chart.
,
eagles, owls and other birds that feed on prey have far more keen eyesight than human beings. The eagle’s eyes are much smaller than human eyes, But there are quite a lot of sensors (cones). This gives the eagle eight times higher vision than human beings, up to 20 / 2!
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