Visual acuity testing is no substitute for a comprehensive eye examination. However, it is one of the most important measurements one can perform when evaluating the human visual system. Visual acuity can be tested at a distance as well as up close.
Distance Visual Acuity: Distance visual acuity is a measurement of your degree of vision loss. It is measured by testing the smallest object that you can recognize, usually on a chart located 20 feet away. This measurement is recorded as a fraction, with 20/20 being considered normal vision. Distance visual acuity is usually tested by isolating each eye and then measuring both eyes together. In most cases, an eye chart is used with various sizes of letters that progressively get smaller and smaller.
Near Visual Acuity: Near visual acuity is a measurement of how well you can see close objects. Usually measured at about 16 inches, it is a good way to measure your ability to cope with tasks such as reading or sewing. In most cases, near visual acuity is measured with both eyes open. You will be asked to hold a near point card at 16 inches and to read the smallest line possible.
Source:
American Optometric Association (AOA). Visual Acuity: What Is 20/20 Vision? AOA, 2006-10.
