Those of you who wear glasses, how often do you replace them?

When I was young, I got new glasses about every 1.5-2 years. Now, I do it about every 4-5 years. Last set of glasses I had (two pairs, since the place I get them at have a deal where it costs either very little or no money to get a second pair) for 5 years before getting my current set. It's been about 3.5 years since then. Probably will wait until 2018 to get new ones.