Eye caregivers use numbers and letters on a chart at a certain distance to measure visual acuity, usually the Snellen eye chart. Almost everyone has had to read letters from one at some point in their lives, whether in the ophthalmologist's office, in the pediatrician's or school nurse's office, or even on the DMV digital eye chart. The most common eye charts used in the United States today are called Snellen charts, named after Hermann Snellen, a Dutch ophthalmologist in the 19th century. This means that the smallest line of the eye chart that can be read at 20 feet can be read by someone with perfect vision who is 100 feet away.
To better understand your visual acuity and how to manage your visual needs, talk to your ophthalmologist and schedule a full eye exam. The second part of the blindness designation is based on your field of vision, which implies how well you can see sideways without moving your eyes. Visual acuity is based on how well you can see with your best eye and with standard corrective lenses, such as prescription glasses or contact lenses. The next time you look at an eye chart, you'll notice that it doesn't contain all the letters of the alphabet.