How to Chart Visual Acuity Using a Snellen Chart

The Snellen chart was developed by Dutch ophthalmologist Herman Snellen in 1862. It's used to measure visual acuity by determining the smallest letters you can read from 20 feet away, and comparing them to what other people can see. Visual acuity is expressed as a ratio, such as 20/40. 20/40 vision means that what you can see at 20 feet is what people with normal vision can see at 40 feet.

Instructions

• 1

  Print out the Snellen chart and tape it to the wall in a well-lit room.

• 2

  Stand 20 feet from the chart.

• 3

  Cover one eye.

• 4

  Try to read the sixth line from the top. If you can read that line correctly, try the seventh line, and continue until you can't read a line correctly. If you can't read the sixth line, try the fifth line and continue upward until you can read a line correctly

• 5

  Check the label adjacent to the lowest line you read correctly. Your visual acuity in the eye you tested is 20/that number.

• 6

  Repeat with the other eye.