20/20 EYESIGHT

What is 20/20 Eyesight? Since the mid-1800s, the term "20/20 vision" has been used to characterize the standard of average, or normal, visual acuity. The 20/20 fraction is based on a measurement system known as the Snellen Chart. This chart, which consists of horizontal lines of black letters that decrease in size from top to bottom on a white background, measures visual acuity, or the ability to distinguish an object from the background. The Snellen Chart may be recognized as the familiar block-lettered "EFPTOZ" poster hanging in many ophthalmology and optometry offices... To measure distance visual acuity using the Snellen standard, patients stand 20 feet - the numerator, or top number in the fraction - away from the chart. The patient then reads the smallest line on the chart that they are able to. The denominator - or the bottom number in the fraction - indicates the comparative distance in feet at which a person with normal eyesight could read the line. For instance, someone with..