I used to find holding water in my mouth while I chopped would help, but the latest batch seem to be more than usually potent. I don't know what variety they are, unfortunately, and I suspect there's a correlation between teariness and tastiness.

I might try refrigerating them for a bit next time, if I remember....

There's a brilliant photo of my brother, aged about ten, peeling onions for my mother to pickle and wearing a diving mask.