The Snellen eye chart was first designed by a Dutch ophthalmologist, Herman Snellen in 1860s. Other types of commonly used eye charts include the Landolt C, and the Lea test.
Below you will find several variations of printable Snellen eye charts you can download and print for home use to determine your visual acuity ie. 20/20 vision.
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 also meets the definition of legally blind.
Visual 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. 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.
Someone with 20/20 visual acuity does not have "perfect" vision, since it is quite possible to see better than 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; in this respect, their vision is much better than human eyesight. Many humans have one eye that has superior visual acuity over the other.
In many modern eye practices today, eye charts may be projected so that they are seen through a series of mirrors. They may also be in the form of wall-mounted or hanging charts. At the top of the chart there is typically a large letter "E" Below that letter, there are rows of capital letters, with each row progressively smaller than the previous one. In some cases, there may be numbers or pictures in place of letters. Some charts may consist of the letter "E" in decreasing sizes, pointing in different directions. This is called the "tumbling"E" chart and is used for people who have difficulty speaking, but can point to indicate which direction the "E" on a certain line on the chart is facing.
Referral to an ophthalmologist should be considered if a persons visual acuity is worse than 20/40, with glasses, if applicable, and visual impairment is interfering with their daily activities.