Why do my eyes burn excessively when I chop onions?

Different types of onions will cause different degrees of irritation. Change the type of onion you're using - from white to yellow and see if it improves. You can also cut the onion submerged in a bowl of water or just use the sink. The water keeps the irritants from getting to your eyes. As a last resort, look in the frozen vegetable section at the grocery store and buy already chopped onions.