Tear gas is a kind of gas within several chemical compounds to cause excessive tearing and irritation. Chloroacetophenone (CN), chlorobenzylidenemalononitrile (CS) and dibenzoxazepine (CR) are the three main compounds used in tear gasses. However, these compounds have the same effect on the eye. The main effect is causing eye irritation and extreme tearing, because people who have been exposed to tear gas cannot see properly and could not be able to keep their eyes open at all. At the same time, it could cause they eyelids to swell as well.
Well, generally speaking, tear gas is very harmful to your health, especially the eyes. First, you should know that tear gas is a blanket term that can be used for any of several chemical compounds that cause excessive tearing and irritation. As you know that it gets its name from its most obvious and characteristic effect. So tear gas can cause eye irritation and extreme tearing. And in some degree, it can just make your eyes become red and bloodshot. Also, the tearing and irritation are often so severe that people who have been exposed to tear gas cannot see properly and might not be able to keep their eyes open at all. By the way, your eyes and eyelids will swell noticeably.
Looks like you are very interested in tear gas, so as far as I know, tear gas contains a lot of chloroacetophenone which is quite irritative to your eyes. You should know that exposure to tear gas could give rise to constant watery eyes, a feeling of wanting to throw up and temporary disability to open your eyes. Anyway, its impacts on your eyes could go away after a while.