Snellen Chart

The Snellen Chart is the most common chart used to test visual acuity. This table was developed by the Dutch ophthalmologist Hermann Snellen in 1862 and has since become widely used in medical practice.

The Snellen chart consists of strings of capital letters called optotypes (test types). The size of letters decreases from line to line from top to bottom. The largest letters are located in the top row of the table; they are of such a size that they can be easily read by a person with normal vision from a distance of 60 meters. A person with normal vision can easily read the lines of letters below from distances of 36, 24, 18, 12, 9, 6 and 5 meters, respectively.

To conduct a vision test, the person whose vision is being tested sits at a distance of 6 meters from the table and closes one eye, while the other begins to read the letters from this table. If he can only read the lines above the line that a person with normal vision can easily read from a distance of 12 meters, then his visual acuity is expressed as 6/12. The lower the number in the denominator, the better the vision. People with normal vision can read one of the bottom lines of letters from a distance of 6 meters, i.e. normal visual acuity is considered 6/6; many people can also read a line that a well-sighted person can read from a distance of 5 meters.

Smaller versions of this table, the creation of which is based on the same principle that was used in the development of its usual version, can be used to test a person’s near vision.

The Snellen chart is an important tool for assessing visual acuity and is used in medical practice, including vision testing when obtaining a driver's license or when visiting an ophthalmologist. It can also be used for educational purposes to demonstrate the principle of vision testing and to explain the concept of visual acuity.

The Snellen Chart is the most common chart used to test visual acuity. This table contains strings of capital letters called test types; the size of letters decreases from line to line from top to bottom. The largest letters are located in the top row of the table; they are of such a size that they can be easily read by a person with normal vision from a distance of 60 meters. A person with normal vision can easily read the lines of letters below from distances of 36, 24, 18, 12, 9, 6 and 5 meters, respectively.

The person whose vision is being tested sits at a distance of 6 meters from the table and closes one eye, while the other begins to read the letters from this table. If he can only read the lines above the line that a person with normal vision can easily read from a distance of 12 meters, then his visual acuity is expressed as 6/12. People with normal vision can read one of the bottom lines of letters from a distance of 6 meters, i.e. normal visual acuity is considered 6/6; many people can also read a line that a well-sighted person can read from a distance of 5 meters.

Smaller versions of this table, the creation of which is based on the same principle that was used in the development of its usual version, can be used to test a person’s near vision.

The most common chart used to test visual acuity is the Snellen chart. It contains lines of capital letters (optotypes) that decrease in size from line to line. The largest letter is located in the first row of the table, and the smallest is in the last.

To conduct the test, a person with normal vision sits at a distance of 6 m from the table and closes one eye. He then begins to read a capital letter located on a line that he can easily read from a distance of 5 m. If he cannot read this line, then his vision is rated as 6/5 (6 meters is the distance at which he sees the letter, 5 meters - the distance from which he can read this letter).

If he can read the line below, his visual acuity is rated 6/6. This means that he can see the letter from a distance equal to the distance at which a person with normal vision sees the same letter.

Thus, the Snellen chart is an effective tool for determining visual acuity and assessing the condition of the human ocular system.