I never used to cry while chopping onions til recently, and I read that contact lenses protect your eyes from the chemical irritants in onions. So it makes sense to me that I'm new to crying while chopping, because I only recently gave up wearing contacts for glasses.
Even with glasses, though, one trick that I've found helpful is to rinse the onion and the cutting knife off under cold water before starting and from time to time while chopping. Not a complete solution, but it helps.