Visual acuity is the ability to distinguish details and shapes of objects.

Also called central vision, visual acuity is a very important statistic in the eye doctor’s office.

A visual acuity test is performed by an ophthalmic (or optometric) technician. It begins by placing an eye chart twenty feet away from a patient and having them read the eye chart to the smallest letters they can see. The visual acuity test is performed one eye at a time. The results are recorded as 20/#. The first number (20) denoting the patient’s distance (in feet) from the chart, the second number denoting the distance (in feet) an eye with perfect vision can read the same line.

A visual acuity reading is the most important element of an eye test. It gives the doctor a gauge, or starting point to determine the health of the eye’s vision. It is important to note that, although a visual acuity reading is paramount to a good quality eye exam, the patient’s perceived vision is just as important. This is why a good history of complaint should be obtained by the eye technician.

Double your distance

You may have noticed that when your eye doctor’s technician tests your visual acuity, she has you look in a mirror, rather than directly at the eye chart. This is a technique that is used in order to achieve the proper 20-feet distance from the eye chart in a room that is not as large as twenty feet. Most exam rooms are around twelve feet long, so the only way to achieve twenty feet away from the eye chart is to reflect the chart’s image off of a mirror – effectively doubling it’s distance.