Assuming you use 20/20 as a baseline and say that standard is 100%, then it is possible to exceed 100%. I have 20/15 in my left eye and 20/13 in my right, therefore better than 100%.
So what about sight enhancements like glasses or binoculars? And now, with corrective eye surgery, the improvement can be better than 20/20 as well. My wife had 20/200 pre-surgery and now 20/15.