Question: what does 20/40 vision or less mean?
Answer: 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.