It is a common sense that the eyes will water when you cut the onions because of the inner irritating materials. However, you could do something to prevent it from happening. You could put the water on the knife and cut the onion. It is a good method for you to prevent the water from the eyes. It is very useful and you could have a try.
It is normal to make tears when cutting an onion, and there are several ways to reduce or eliminate the issue. One most effective way is keeping the onion in the ice box until they are chill that can inhibits the release of the enzyme into the air. Or you can put the onion under water when cutting it to eliminate the gas comes into air to stimulate tear film. On the other hand, you can use a sharp knife for a cleaner cut to reduce the enzyme. Instead of changing the way you cut, you can change the physical environment. Light a candle and place it within a couple of feet of your chopping area. The flame draws the vapors from the onion and prevents tears.
Well, generally speaking, you should know that it's normal to have watery eyes when you cut onions. As we know that there are kinds of objects which have the irritant function. So when you cut them, it will irritate your tear system and make you just like cry. In my opinion, you can breathe through mouth while cutting onions and the mouth is open. From my own experience, after trying this I stopped shedding tears and you know I suggested it for lot of peoples and it is working like anything. Maybe you can have a try. Also, you can just console it with your eye doctor, maybe he can give some advices.