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. A comprehensive eye examination by a doctor of optometry should identify causes, if any, that are affecting an individual's ability to see well. In most cases, the optometrist can prescribe glasses, contact lenses or a vision therapy program that will help improve vision. If the reduced vision is due to an eye disease, the use of ocular medication or othertreatment by an ophthalmologist may be required.