How is visual acuity measured?

How is visual acuity measured?

“Having 20/20 vision” means perfect vision. The top number is the standardized testing distance used, which is 20 feet. The bottom number represents the smallest letter size you can read. So if you have 20/40 vision, it means you need to be within 20 feet to read a letter that someone with perfect vision could see clearly at 40 feet.