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BookmarkVisual acuity (VA) is acuteness or clearness of vision, especially form vision, which is dependent on the sharpness of the retinal focus within the eye, the sensitivity of the nervous elements, and the interpretative faculty of the brain. VA is a quantitative measure of the ability to identify black symbols on a white background at a standardized distance as the size of the symbols is varied.
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The VA represents the smallest size that can be reliably identified.
VA is the most common clinical measurement of visual function.
A visual acuity of 20/20 is frequently described as meaning that a person can see 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, he is said to see detail from 20 feet away the same as a person with normal eyesight would see it from 40 feet away.
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 (6/3).
Recent developments in optometry have resulted in corrective lenses conferring upon the wearer a vision of up to 20/10.
Some birds, such as hawks, are believed to have an acuity of around 20/2, which is much better than human eyesight.
Many humans have one eye that has superior visual acuity over the other.
If a person cannot achieve a visual acuity of 20/200 (6/60) or above in the better eye, even with the best possible glasses, then that person is considered legally blind in the United States.
A person with a visual field narrower than 20 degrees in diameter also meets the definition of legally blind..
For more information about the topic Visual acuity, read the full article at Wikipedia.org, or see the following related articles:
Eye examination — An eye examination is a battery of tests performed by an ophthalmologist or optometrist assessing vision and ability to focus on and discern objects, ... > read more
Visual field — The term visual field is often used in ophthalmology, where a visual field test is used to determine whether the visual field is affected by diseases ... > read more
Visual perception — Visual perception is one of the senses, consisting of the ability to detect light and interpret (see) it as the perception known as sight or naked ... > read more
