The different types of eye charts include the Snellen chart, the Landolt C chart, the logMAR chart and the Jaeger chart. The Tumbling E chart is a modification of the Snellen chart for the very young or the illiterate who do not recognize the letters of the alphabet.
Ophthalmologists measure a patient's visual acuity by having the patient identify the test symbols on an eye chart. If a patient recognizes test symbols accurately at a distance of 20 feet, the patient has normal visual acuity, which is also known as 20/20 vision.
Eye charts are only one part of a complete eye exam and do not measure peripheral vision, depth perception, eye fluid pressure or the dryness of the eyes. Thus, doctors only use them to figure out whether a patient needs glasses or contact lenses to correct any vision problems.