snellen chart
Noun: A Snellen chart is a standardized tool used in optometry and ophthalmology to measure a person's visual acuity, or clarity of vision. It consists of rows of letters, numbers, or symbols (optotypes) that progressively decrease in size from the top row to the bottom.
The Snellen chart is used in a clinical setting to determine how well a person can see details at a standard distance, typically 20 feet (or 6 meters). The patient is asked to read the smallest line of characters they can discern clearly. The results are expressed as a fraction (e.g., 20/20 vision), where the numerator is the testing distance and the denominator is the distance at which a person with normal vision could read the same line.
- Noun:
- The optometrist asked me to cover one eye and read the letters on the Snellen chart.
- A standard Snellen chart has 11 rows of block letters.
- "to read the Snellen chart": to perform the visual acuity test.
- All new drivers must read the Snellen chart as part of their license application.
- Visual acuity chart: A more general term for any chart designed to test clarity of vision, with the Snellen chart being the most common type.
- LogMAR chart: A more modern, scientifically designed chart that uses a logarithmic progression of letter sizes, often used in research settings.
- Tumbling E chart: A variation of the acuity chart using only the letter 'E' in different rotations, used for testing individuals who cannot read letters (e.g., children or illiterate patients).
- Eye chart: A common, informal synonym.
- Acuity chart: A more technical synonym focusing on its function.
The chart is named after the Dutch ophthalmologist Hermann Snellen, who developed it in 1862. It remains one of the most universally recognized medical instruments.
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display consisting of a printed card with letters and numbers in lines of decreasing size; used to test visual acuity
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