The vision test is the simplest yet most important component of the eye exam.  In order for eye doctors to compare results, it's always done at a standardized distance of twenty feet.  Old-fashioned offices had rooms that were twenty feet long.  Today, mirrors are used to reflect the image so the room can be shorter; but the image still looks like it is twenty feet away.  The charts are standardized too and doctors around the world use the same basic format.  But what do those numbers mean?

Each line of the eye chart is assigned a notation in the form of a fraction that represents your visual acuity.  The numerator is the distance in feet the patient is from the eye chart.  The denominator, represents the distance an eye with "normal" vision can read the same line.  Interpreting the numbers is simple.  If a patient reads the 20/40 line, he is able to see at 20 feet what a normal eye could see at 40.  And if your vision is 20/16?  You're above average because you can see an object from 20 feet that a normal eye sees at 16!