请问视力20/40相当于国内的几度近视啊?!
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haha,I got it
“20/20” means the smallest letters you can recognize at a distance of 20 feet are the same size as those a person with normal eyesight can see at the same distance. You have normal (20/20) eyesight.
if you have 20/40 visual acuity, the smallest letters you can recognize at 20 feet a person with normal eyesight can recognize when they are 40 feet away. In other words, your visual acuity is only half as clear as that of a person with normal eyesight (20/40 = 50%).
“20/20” means the smallest letters you can recognize at a distance of 20 feet are the same size as those a person with normal eyesight can see at the same distance. You have normal (20/20) eyesight.
if you have 20/40 visual acuity, the smallest letters you can recognize at 20 feet a person with normal eyesight can recognize when they are 40 feet away. In other words, your visual acuity is only half as clear as that of a person with normal eyesight (20/40 = 50%).
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Visual acuity is usually measured with a Snellen chart. The Snellen chart displays letters of progressively smaller size. "Normal" vision is 20/20. This means that the test subject sees the same line of letters at 20 feet that a normal person sees at 20 feet. 20/40 vision means that the test subject see as 20 feet what a normal person sees at 40 feet. Another way of saying this is that a person with 20/40 vision has vision that is only half as good as normal - or, objects must be at half the normal distance for him to see them. A person with 20/20 vision is able to see letters 1/10th as large as someone with 20/200 vision. However, 20/15 vision is better than 20/20. A person with 20/15 vision can see objects at 20 feet that a person with 20/20 vision can only see at 15 feet.
Levels of Vision
20/20 - Normal vision. Fighter pilot minimum. Required to read the stock quotes in the newspaper, or numbers in the telephone book.
20/40 - Able to pass Driver's License Test. Most printed material is at this level.
20/80 - Able to read alarm clock at 10 feet. News Headlines are this size.
20/200 - Legal blindness. Able to see STOP sign letters.
Levels of Vision
20/20 - Normal vision. Fighter pilot minimum. Required to read the stock quotes in the newspaper, or numbers in the telephone book.
20/40 - Able to pass Driver's License Test. Most printed material is at this level.
20/80 - Able to read alarm clock at 10 feet. News Headlines are this size.
20/200 - Legal blindness. Able to see STOP sign letters.
