Write an article based on this "Position yourself about 6 metres (20ft) from the Snellen chart. Cover one of your eyes with the palm of your hand. Read the lowest line that you're able to on the Snellen chart. Repeat the steps with your other eye."
The Snellen chart is the large chart found in all doctor's offices which features the letters of the alphabet, arranged in 8 rows at random, in decreasing size. In most optic-nerve exams, the optometrist or an assistant will direct you where to stand or sit. The Snellen chart is meant to be read with only one eye at a time, in order to test the acuity of each eye individually. In some cases, the doctor may provide a plastic spoon-like utensil that you can use to cover your eye. Otherwise, cover the eye completely with the palm of your hand. If you routinely wear glasses or contact lenses, keep them on for the exam unless the doctor directs you to do otherwise. Visual acuity is a numerical value derived by as your distance from the chart over the number of the lowest line that you correctly read. For example, 20/20 (or 6/6, using meters) is perfect vision. Lower lines on the chart feature smaller letters, meaning that you'll most likely be unable to read the lowest 2 or 3 lines. Pick a line on the bottom half of the chart, and read the letters as best you can. Following this reading, the doctor may ask you to attempt to read a higher or lower line on the chart. A line is considered to have been successfully read if you misread 2 or fewer letters. Once you've read the lowest possible line with one eye, remove your hand and use it to cover your other eye. Then begin the process over again by attempting to read a low line on the Snellen chart with your second eye covered. Once you've finished the acuity exam with your second eye, you can ask the doctor what your acuity score was.