Since Europe and most parts of the world use the metric system, the World Health Organization uses meters in its definitions. In the United States, visual acuity is measured at a distance of 20 feet. In Europe and the rest of the world visual acuity is measured at a distance of 6 meters.? (Note that 20 feet equals approximately 6 meters.)?

"Normal vision" is therefore defined as a distance visual acuity of 6/6 (or 20/20 in US terms) with a full visual field of 180 degrees.? Distance visual acuity is that most central part of vision that is used to see objects at a distance.? "6/6 or 20/20" means they can see a specific line of letters when they are standing or seated 20 feet or 6 meters away from an eye chart.

The loss of visual acuity causes blurred vision and you cannot see objects at a distance clearly.?