How is vision measured?
I know my vision is bad. Since I was less than ten years old I’ve had to wear glasses or contacts because my vision is much worse than 20/20. I always wondered what 20/20 meant, so this week I looked it up. Normal vision, or acuity, is tested by reading an eye chart at a distance of 20 feet and comparing your vision to what should be seen from that distance by the majority of the population. So if you’re 20 feet back from the chart and see everything clearly your vision is 20/20. If you’re 20 feet back and you see what someone with normal vision sees at 100 feet back then your vision is 20/100. The cutoff to be legally blind is 20/200. If you see at 20 feet back what the average person sees at 10 feet back, then your vision is measured as 20/10 and is better than normal.
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