Do you have the issue that when you chop up onions they make you cry? I have been known to resort to wearing ski goggles to stop this happening. Tears stream down my eyes and I have to go outside for fresh air before I can finish chopping. I have tried sticking brown bread in my cheeks, burning a candle near by, having the window open but nothing really worked and white onions basically had to be avoided at all costs.
The reason for our eyes watering is that when we cut into an onion, it releases a sulphuric acid that reacts with the moisture in our eyes and creates a burning sensation which in turn makes the eyes water.
So to help in this situation, take your onion, and chop off the top, then cut in half but do not remove the bottom (the root) and just peel back the outer thicker skin. From here you can chop finely, in slices or how ever you wish and just do not take off the final roots till the last cut.
I hope this tip works for you!