They say hindsight is 20/20, but what does that number mean exactly? These numbers follow a grading system used by your eye doctor to measure visual acuity— that is, the clearness of your eyesight. It’s a measure of the focal length for both your eyes with the first number representing your left eye and the second number is for your right. The higher the numbers are, the shorter the focal length is, which means you likely have to move objects much closer to your face just get a good look at them.