A Snellen Eye Chart is an eye chart used by eye care professionals and others to measure how well you see at various distances. The traditional Snellen Eye Chart is printed with eleven lines of block letters. The first line consists of one very large letter, an E. Subsequent rows have increasing numbers of letters that decrease in size. A patient taking the Snellen Eye Chart test covers one eye, and reads aloud the letters of each row of the Snellen Eye Chart, beginning at the top. The smallest row that can be read accurately indicates the patient's visual acuity in that eye. Wall-mounted Snellen Eye Charts are inexpensive and are sometimes used for rough assessment of vision, e.g. in a primary-care physician's office. Plastic.