If I need a new pair of glasses with the same prescription I have now (Say, for example, I fall and break my glasses), I shouldn't be required to go get examined to get a new pair simply because it has been more than a year. I want the same thing I've been wearing, and the worst possible outcome from me getting them is that (if my prescription has worsened, which it hasn't in 4+ years) I can't see quite as clearly at long range as I ought to.