What is 20/20?
Hopefully your eye exam will find your vision to be 20/20, but what does that mean and how does it compare to everyone else out there? In the US, the ability to see visual detail (visual acuity) is described in a fraction. The first number indicates the distance to the visual target. This is 20 feet for the standard in the US and 6 meters for most other countries. Most exams rooms are not 20'. This is why it's common to see mirrors which lengthen the target distance in smaller exam rooms. The second number is the size of the target letter. For 20/20, the target letter is 8.87mm (0.35") tall by 8.87mm wide. Therefore, 20/20 is the ability to identify an 8.87mm character at 20'. Of course some letters are easier to identify than others. Letters with straight lines, such as an "E" are more readily recognized than circular letters "O". Straight lines provide more clues to the brain as it is putting the visual picture together. Some patients may no...