What is an eye chart?

An eye chart is used to measure the eye's ability to see details at near and far distances.It is used to evaluate eyesight.
The eye tests usually involve reading letters or looking at symbols of different sizes on an eye chart. Usually,each eye is tested by itself. And then both eyes may be tested together, with and without corrective lenses (if you wear them).

Types of eye charts include the logMAR chart, Snellen chart, Landolt C, and the Lea test.The Snellen Chart is the commonly used eye chart by the doctors. It has standard size letters and is normally viewed at a test distance of 20 feet. It is used to determine your visual acuity ."Visual"refers to the clarity or clearness of the vision and the word "acuity" comes from the Latin "acuitas" meaning sharpness.

smiling woman with beautiful eyes and smiling face with cap on head

Eye Charts are available for very young children or illiterate adults that do not require letter recognition. One version uses simple pictures or patterns. Others are printed with the block letter "E" turned in different orientations, the so called Tumbling E. The patient simply indicates which direction each "E" is facing.

The Landolt C chart is similar: rows have circles with different segments missing, and the test-taker describes where each broken piece is located. The last two kinds of charts also reduce the possibility of the patient guessing the images.

Eye Charts usually display several rows of optotypes (test symbols), each row in a different size. An optotype is a standardized symbol for testing vision. Optotypes can be specially shaped letters, numbers, or geometric symbols.

The person is asked to identify the optotype on the chart, usually starting with large rows and continuing to smaller rows until the optotypes cannot be reliably identified anymore.The top row is imprinted with a single letter usually " E" bigger in size. The other rows contain letters which will go decrease in size.

Technically speaking, testing visual acuity with an eye chart is a psychophysical measurement that attempts to determine a sensory threshold.

Eye Chart

The above image is the Snellen chart.In that 20/20 vision (or really, 20/20 visual acuity) is considered "normal" vision, meaning you can read at 20 feet a letter that most human beings should be able to read at 20 feet.

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