Eye exam charts, or Snellen eye charts, are available online at the websites of Vision Source or Disabled World. Vision Source has one eye chart available for print, whereas Disabled World has four printable eye charts.
Because the desired use of printing out eye charts is to determine visual acuity, it is necessary to print and use the charts exactly as directed. To use the eye chart properly, stand 20 feet away from the chart in a well-lit room that is not exposed to harsh sunlight. Have a second person point out each line and note which letters are seen incorrectly. The lowest line that is read with a majority of correctly seen letter determines visual acuity.
The term 20/20 vision is derived from the Snellen eye chart. Having 20/20 vision, or visual acuity, indicates that the person can see things 20 feet away just as clearly as someone else who has normal vision would be able to see at the same distance.
The Snellen eye chart does not measure peripheral vision, nor depth, color and contrast perception. Additionally, it cannot detect the health of the eyeball. Because of these reasons it is recommended that every person should get a full eye exam every two years.