How is a Snellen Test Chart used to diagnose late adult onset myopia?

The Snellen Test Chart is the eye test you always think of when going to the eye doctor. It is the chart with the letters that get smaller in each row. The eye doctor asks you to cover an eye and read the lines. During this test, you are about 20 feet away from the chart. This is done to evaluate your distance vision, identifying how well you see at 20 feet.