20/20

Why is normal vision referred to as 20/20?

Visual acuity is expressed as a fraction. The top number refers to the distance you stand from the chart. This is usually 20 feet. The bottom number indicates the distance at which a person with normal eyesight could correctly read the line with the smallest letters. Normal vision is considered 20/20. If your vision is 20/40, the line you correctly read at 20 feet could be read by a person with normal vision at 40 feet.

If your optometrist says you have 20/60 vision, that means you are able to discriminate characters at 20 feet away from an eye chart that a person with normal acuity can see at a distance of 60 feet.

Of course, just because 20/20 vision is normal doesn't mean it's perfect. A small percentage of the population is blessed with vision better than 20/20, and just recently researchers unveiled corrective lens that offered vision closer to 20/10.

我諗我頂多都係睇到第５行 ^^"

P.S: 我諗外國個20/20 新聞節目就係用呢樣野來命名，來表達清楚看到事實的意思。