20/20 Vision and Visual Acuity

20/20 vision is a measurement of visual acuity, which means it measures how well you can see.

20/20 visual acuity means that a person can see small detail from 20 feet away the same as a person with normal eyesight would see from 20 feet. If a person has a visual acuity of 20/40, they are said to see detail from 20 feet away the same as a person with normal eyesight would see it from 40 feet away.

Eye glasses sitting on an eye exam chart
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Snellen Visual Acuity

Dutch ophthalmologist, Herman Snellen developed Snellen visual acuity in 1862. Snellen visual acuity is represented as the distance at which the test is performed over the distance at which the smallest identified shape or letter is seen.

An optotype is a standardized letter, shape, picture, or number that a person is asked to name or describe when their vision is tested. Specifically, the smallest optotype subtends an angle of 5 minutes of arc and the detail of that optotype subtends 1 minute of arc.

Normal Vision

20/20 vision is considered normal, but it does not necessarily mean perfect vision. Having 20/20 vision only indicates the clarity of vision at a distance. It doesn't measure the quality of vision or the skills needed to have good vision, such as eye-hand coordination, accommodative ability, depth perception, peripheral vision, or color vision.

You can sometimes have 20/20 vision even if you have a visual field cut. which means that you can't see an area of vision.

Furthermore, having 20/20 vision does not necessarily mean your eye is perfectly healthy. For example, you can be farsighted, but still measure 20/20 visual acuity with no glasses on. Farsighted people sometimes have the ability to focus harder and compensate for farsightedness. However, holding your focus for a long period of time is exhausting, and eventually, vision can become blurry.

Superior Vision

20/20 vision is considered normal vision. It is possible to have vision superior to 20/20.

The maximum acuity of the human eye without visual aids (such as binoculars) is generally thought to be around 20/10. This means that a person can see detail from 20 feet away the same as a person with normal eyesight would see it from 10 feet away.

Other Ways to Measure Visual Acuity

How do you measure visual acuity for someone who doesn't know the letters or who can't speak or is maybe just too shy to speak? There are a few different methods.

Tumbling E Visual Acuity Chart

The Tumbling E chart uses the same measurement scale as the typical Snellen Eye Chart. However, all of the optotypes used on the chart are the capital letter E, displayed in different orientations.

In this case, a person is shown a letter to read on the eye chart and can simply use their fingers to show the tester what direction the E is pointing.

LEA Vision Test

The LEA test is a visual acuity test designed for children who cannot read letters. The test uses for optotypes: an apple, a pentagon, a square, and a circle. The test uses these common symbols so that visual acuity can be measured at a much younger age.

Jaeger Eye Chart for Near Vision

If you have had an eye examination, you may have been shown a Jaeger eye chart to test your near visual acuity. The Jaeger chart is a small handheld chart that shows blocks of text in various sizes. Instead of using the term 20/20, The Jaeger chart uses a scale that ranges from J1 to J11. J2 is usually considered equal to the typical 20/20 measurement. The chart is usually held between 12-16 inches from your eyes.

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3 Sources
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