Snellen chart

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The Snellen Eye 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. The Snellen chart is the most commonly used way of testing if someone has sufficient corrected visual acuity to drive legally. There is no direct correlation between visual acuity and myopia. Your optometrist will use the Snellen chart as a reference, to see what refraction will allow you to read the lowest on the chart.

How to use a Snellen Chart to measure Acuity

  1. Read the documentation that came with your chart to determine what distance it is designed to be viewed at. This is usually 10 feet, 20 feet, 3 m or 6m. It may say right on the chart, on the back, or in the description of the product where you got it.
  2. Post the chart at eye level
  3. Make a mark on the floor at the distance the chart is rated for.
  4. Stand so that your face is above that line.
  5. Read the lowest line you can see clearly.
  6. Attempt to read the next line down.
  7. Have an assistant tell you if you got the letters right or move forward to check. If you got most of the letters right on that line, then the ratio marked for that line is your visual acuity.

How to use a Snellen Chart with Refraction

See: trial lens kit

References