Visual acuity is usually measured with a Snellen chart. "Normal" vision is 20/20. This means that the test subject sees the same line of letters at 20 feet that person with normal vision sees at 20 feet. 20/40 vision means that the test subject sees at 20 feet what a person with normal vision sees at 40 feet.
Also question is, is it bad to have 20 30 Vision?
20/15 vision means that at 20 feet you can see what a normal person would be able to see at 15 feet. Meaning you can be 5 feet further away than they can. 20/30 vision means at 20 feet you can see what a normal person would be able to see at 30 feet. So your vision is not as good as someone with 20/20.
How good is 20 13 Vision?
It means very sharp vision. When we say you have “20/20 vision,” it means what someone with perfect vision can read at 20 feet, you also can. In this case, the average “perfect vision” person would need to approach to 13 feet to visualize clearly what the “20/13” can read at 20 feet.
What does it mean Vision 20 30?
For example, if you have 20/30 vision, it means your vision is worse than average. When you are standing 20 feet from the chart, you can read letters that most people see when they are 30 feet away. A standard Snellen vision testing chart. However, 20/20 vision is not perfect vision.