I took off to the store last summer on my bike and just before rounding the corner at the end of the block what felt at first like a small bug got in my eye. It was so painful it forced me to come to a dead stop and use my bottled water to rinse my eyes for nearly 5 minutes. The pain subsided a little but didn't go away and by the time I returned from the store the entire white of my eye was bloodshot and the level of pain, itching and redness were getting even worse. looking back I think it must have been a drop of formic acid from a bee or wasp in the overhanging tree - a one in 10 million chance that it would hit me in the eye.
After about 30 minutes in the hospital under an eye wash device (not the most comfortable thing either) I recovered enough to leave. Eventually with the help of prescription eye medication the pain subsided and the redness slowly went away.
Here now is what I could have done had this instructables been around before rushing off to the store for an "emergency" can of ...err soda.