Someone with "20/30 vision" stands 20 feet from a reading chart but sees letters and objects that people with normal vision see 30 feet away from the chart, according to the University of Iowa. The first number, 20, is the distance from the eye chart and the second number, 30, shows the size of the letters read at that distance.
A patient with 20/30 vision may need corrective lenses to see properly. The University of Iowa also explains that about 35 percent of Americans have 20/20 vision, meaning they see things normally. Having 20/20 vision describes someone who has sharp, clear vision at a distance. The American Optometric Association explains that other factors including depth perception, peripheral vision and color discernment determine a person's overall seeing ability.
The ability to see from a certain distance is measured by an eye chart hanging on a wall. The chart has 11 rows of letters, with a large "E" at the top. A patient able to read the "E" and nothing else on the chart has 20/200 vision, according to All About Vision. Having 20/200 vision is the definition of legal blindness in the United States. Drivers of vehicles need to have at least 20/40 visual acuity with corrective lenses. The line of 20/20 vision is the fourth row from the bottom of the chart. If a person can read the very bottom line of the chart, that person has 20/5 vision.