According to Eye Care Fun, 20/40 vision is worse than normal vision and may require glasses, depending on the precise form of the vision problem. A person with vision 20/40 can see objects at a distance of 20 feet that a person with normal vision can see at a distance of 40 feet.
Normal vision is defined as 20/20, according to Eye Care Fun. In the United States, a person who cannot obtain vision of at least 20/200 with the aid of corrective lenses is considered legally blind. If a person has peripheral vision of less than 20 degrees, they are also deemed legally blind.
According to Wikipedia, vision, often known as visual perception, is the interpretation of the environment through the information contained in light. The academic disciplines of neuroscience, biology, and psychology do study on the visual system components.