Flush your eyes with water. Don't put any eye drops into eyes, because the mouth wash chemical would react anything else which can lead to some damage and make things worse.
If the pain continues after several days, you must go to hospital for help. Your doctor will look at it carefully and give you the best medication for your eye.
It is terrible to get somthing into eyes. Your eyes may burn and become extremely red. Rinse them immediately with plenty of water. Using water to wash your eyes, if necessary, get someone to help you open your eyes. Your eyes may be tearing a lot, which means eyes are trying to wash the mouthwash out too, so don't worry about it. After a while, you will be fine. Just please be more careful. If you still feel very uncomfortable of your eyes, you must go to see the doctor.
Yes, of course, because mouthwash is such an irritated stuff which would lead to some extremely uncomfortable feelings. So, for the time being, you gotta get some hot water to flush your eyes. Try not to rub your eyes because it is infectious. And if things don't turn out right, go to see a doctor. Generally speaking, such kind of thing is not that serious, take it easy.