Acuity is the measure of the eye’s ability to distinguish the smallest identifiable letter or symbol, its details and shape, usually at a distance of 20 feet. This measurement is usually given in a fraction. The top number refers to the testing distance measured in feet and the bottom number is the distance from which a normal eye should see the letter or shape. So, the perfect vision is 20/20. If your vision is 20/60, that means what you can see at a distance of 20 feet, someone with perfect vision can see at a distance of 60 feet.