Consequently, a brief overview may help. It only indicates the sharpness or clarity of vision at a distance. 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 one's 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 nearsightedness, farsightedness or astigmatism or from eye diseases. Clarity of vision does vary with distance. 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.