A chart commonly used by opticians to test eyesight [Described 1862. After Hermann Snellen (1834—1908), Dutch ophthalmologist.]
A display showing letters arranged in lines of increasingly smaller size and used to test sharpness of vision. Typically the person is asked to read the letters on the line that can be seen by people with perfect vision from 20 feet away. If the person can do this, he or she is said to have 20/20 vision. If vision is less sharp — if, for example, the person can read at 20 feet that which a person with normal vision can read at 60 feet — he or she has 20/60 vision. Testing with the Snellen chart is part of a standard eye examination.
The commonest chart used for testing sharpness of distant vision. It consists of rows of capital letters, called test types, the letters of each row becoming smaller down the chart. The large letter at the top is of such a size that it can be read by a person with normal sight from a distance of 60 meters. A normally sighted person can read successive lines of letters from 36, 24, 18, 12, 9, 6, and 5 meters respectively. There is sometimes a line for 4 meters. The subject sits 6 meters (20 feet) from the chart and one eye is tested at a time. If he can only read down as far as the 12-meter (40-foot) line the visual acuity is expressed as 6/12 (or, if in feet, 20/40). Normally sighted people can read the 6-meter (20-foot) line, i.e. normal acuity is 6/6 (or, if in feet, 20/20), and many people read the 5-meter line with ease. A smaller chart on the same principle is available for testing near vision.
The most commonly used chart for testing the acuity of distant vision. The chart comprises rows of capital letters, with the letters in each row being smaller than those in the one above. The top line of large letters can be seen by a normally sighted person standing 60 metres away. The subject under test sits 6 metres from the screen and, if he or she can read the 6-metre line of letters, his or her visual acuity is normal at 6/6.
The Snellen chart is a technique employed in vision assessments to determine visual acuity. This chart consists of multiple rows of letters, each row standardized in size and progressively smaller than the one preceding it. During the test, the patient stands at a distance of 6 meters from the chart. One eye at a time is covered, and the patient is instructed to read the letters down the chart using the uncovered eye, reaching as far down as they can accurately identify.