![]() ![]() If you can identify the letters on this line but none smaller, you have normal (20/20) visual acuity. In the United States, this distance typically is 20 feet in other countries, it is 6 meters.Īt this testing distance, the size of the letters on one of the smaller lines near the bottom of the eye chart has been standardized to correspond to “normal” visual acuity this is the “20/20” line. In the Snellen visual acuity system, the top number of the Snellen fraction is the viewing distance between the patient and the eye chart. They also are called Snellen fractions, named after Herman Snellen, the Dutch ophthalmologist who developed this measurement system in 1862. The term “20/20” and similar fractions (such as 20/40, 20/60, etc.) are visual acuity measurements. For better or worse, the term “20/20 vision” is likely here to stay. If this more inclusive (and accurate) definition of “vision” is used, what most people call “20/20 vision” should really be called “20/20 visual acuity.” Realistically, that probably won’t happen. These include contrast sensitivity, the ability to track moving objects with smooth and accurate eye movements, color vision, depth perception, focusing speed and accuracy, and more. In addition to sharpness of sight or simply a description of the ability to see, the term “vision” usually includes a wider range of visual abilities and skills. Vision. This is a broader term than visual acuity or eyesight. Depending on which dictionary or other resource you check, it can mean “ability to see,” “the sense of seeing,” “vision,” “range of sight” or “view.” Often, the terms “eyesight” and “visual acuity” are used interchangeably. ![]() Visual acuity typically is quantified with Snellen fractions (see “What is 20/20 Vision?” below).Įyesight. The exact definition of “eyesight” is difficult to pin down. Only light that is focused on a very small and highly sensitive portion of the central retina (called the macula) influences visual acuity measurements obtained during an eye exam. The ability of the brain to interpret information received from the eyes.The sensitivity of the nerves in the retina and vision centers in the brain.How accurately the cornea and lens of the eye focus light onto the retina.Three major physical and neurological factors determine visual acuity: Objects that are similar in brightness to their background.For example, it can’t predict how well you would see: Visual acuity also is tested under high contrast conditions - typically, the letters or numbers on the eye chart are black, and the background of the chart is white.Īlthough visual acuity testing is very useful to determine the relative clarity of your eyesight in standardized conditions, it isn’t predictive of the quality of your vision in all situations. Visual acuity is a static measurement, meaning you are sitting still during the testing and the letters or numbers you are viewing also are stationary. Visual acuity is tested one eye at a time, with the help of a standardized Snellen eye chart.
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