If you have 20/20 visual acuity, you can read a letter from 20 feet away that the “average” human being can also read from a distance of 20 feet. Together, these numbers represent a comparison between what the “average” person should be able to see from a distance of 20 feet and what we can actually see. The large letter “E” on top on most charts corresponds to 20/200 visual acuity, and each subsequent line correlates to clearer visual acuity-20/20 being standardized as “normal” acuity. When viewed at this distance, the bottom number of the Snellen fraction corresponds to a line of text on the eye chart. This is typically 20 feet in the United States and 6 meters in other countries throughout the world. The top number of the Snellen fraction refers to the viewing distance between the patient and the eye chart. Herman Snellen developed his system for measuring visual acuity in 1862, and it remains the most commonly used method today. This is why most standard eye charts show black letters or numbers on a white background or vice versa.Ģ0/20 and other visual acuity measurements (such as 20/40, 20/60, etc.) are known as Snellen fractions. Visual acuity is also normally tested in high-contrast conditions. This is usually a static measurement, meaning you are standing still and the text being viewed is also stationary. When your doctor asks you to identify letters or numbers on an eye chart, they are testing your visual acuity or the sharpness of your vision. While all of these skills are important, “20/20 vision” is really only describing one aspect of our sight-visual acuity. These include color vision, contrast sensitivity, depth perception, the ability to smoothly track moving objects, and more. Vision is a broad description of our eyesight that covers a wide range of visual skills and abilities. The Difference Between Visual Acuity And Our Visionīefore we explore what those magic numbers mean, it’s important to clarify what we’re measuring when we say someone has “20/20 vision.” Even though we can reflect on past experiences through a seemingly perfect lens, is 20/20 as good as it gets when it comes to our vision?
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