• 20/400
• 20/200
• 20/100
• 20/70
• 20/50
• 20/40
• 20/30
• 20/25
• 20/20

The Snellen test is a wall chart consisting of several lines of letters. The letters on the top line are the largest; those on the bottom line are the smallest. To test your ability to see at far distances, you will stand 20 ft (6 m) from the chart. You will be asked to cover one eye with your hand or with a handheld cover (occluder) and then read the smallest line of letters you can see on the chart. If you are unable to cover your eye, an eye patch will be placed over the eye.

When you have completed the test with one eye, you will cover your other eye and repeat the process. You may be asked to read a different chart or to read the lines backward to make sure that you did not remember the sequence of letters from the previous test.

If you wear glasses or contacts, you will be asked to repeat the test on each eye while wearing them.

If you have difficulty reading the letters on one side of the line, or if some letters disappear while you are looking at other letters, you may have a visual field defect. Let the health professional know if you notice this. Visual field tests may then be needed.