Difference between revisions of Snellen chart
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A '''Snellen chart''' is a standard method of measuring [[visual acuity]]. A chart is rated for the distance it should be viewed at, and the lowest line that can be read has a visual acuity result number next to it. The standard distance for Snellen charts is 20 feet or 6 meters. Smaller versions are available for use in smaller indoor spaces. Generally, most myopes can be corrected to the [[20/20]] line unless they have visual acuity problems other than myopia. There is no direct correlation between visual acuity and [[myopia]]. The Snellen chart is the most commonly used way of testing if someone has sufficient corrected visual acuity to drive legally. Your [[optometrist]] will use the Snellen chart as a reference, to see what refraction will allow you to read the lowest on the chart. | A '''Snellen chart''' is a standard method of measuring [[visual acuity]]. A chart is rated for the distance it should be viewed at, and the lowest line that can be read has a visual acuity result number next to it. The standard distance for Snellen charts is 20 feet or 6 meters. Smaller versions are available for use in smaller indoor spaces. Generally, most myopes can be corrected to the [[20/20]] line unless they have visual acuity problems other than myopia. There is no direct correlation between visual acuity and [[myopia]]. The Snellen chart is the most commonly used way of testing if someone has sufficient corrected visual acuity to drive legally. Your [[optometrist]] will use the Snellen chart as a reference, to see what refraction will allow you to read the lowest on the chart. | ||
You can check your own eyesight at home with the free [https://start.endmyopia.org/tools/online-eye-test online eye test], which sizes a real letter chart to your screen and your distance. | |||
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==Definition of the numbers== | ==Definition of the numbers== | ||
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# Make a mark on the floor at the distance the chart is rated for. | # Make a mark on the floor at the distance the chart is rated for. | ||
# Stand so that your face is above that line. | # Stand so that your face is above that line. | ||
# Gently cover one eye (without actually touching it) | # Gently cover one eye (without actually touching it). | ||
# Read the lowest line you can see clearly. | # Read the lowest line you can see clearly. | ||
# Attempt to read the next line down. | # Attempt to read the next line down. | ||
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# Repeat steps 5-8 with the other eye covered. | # Repeat steps 5-8 with the other eye covered. | ||
# Repeat once more with both eyes together. | # Repeat once more with both eyes together. | ||
Please note: Unless you are in low myopia territory snellen measurements are intended to measure your vision with your distance correction. | |||
Also important to know: Lighting will effect your results and due to the nature of the diopter bubble longer charts (6m/20ft) are more accurate than the short charts (3m/10ft), though both are perfectly acceptable methods to track vision trends over time. | |||
==How to use a Snellen Chart with refraction== | ==How to use a Snellen Chart with refraction== | ||
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* [[Astigmatism_measurement]] | * [[Astigmatism_measurement]] | ||
* [Guide:How to measure your eyesight] | * [[Guide:How to measure your eyesight]] | ||
==References== | ==References== | ||