There are other important vision skills, among them peripheral awareness or side vision, eye coordination, depth perception, focusing ability and color vision that contribute to your overall vision ability. For consistency, optometrists in the U.S. use 20 feet as the standard to express sharpness of vision. Other countries express visual acuity in their own way.
Visual acuity is affected by many factors.
Less than optimum clarity may result from vision conditions like near sightedness, farsightedness or astigmatism or from eye diseases. Some people can see well at a distance, but are unable to bring nearer objects into focus. Others can see items that are close, but cannot see those far away. This condition may be caused by nearsightedness. A comprehensive eye examination by a doctor of optometry should identify those causes, if any, that are affecting your ability to see well.