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.
Step 1: Acquire a 3 liter (or 2 liter) soda bottle
Even a 2 liter bottle will do. This 3 liter one came from a supermarket which regularly stocks the 3 liter size.
Step 2: Cut off the top and bottom.
I forgot to leave the label on as a cutting guide so my edges had to be trimmed quite a bit before I was done. Leave the label on and cut along both the top and bottom edge.
Step 3: Now cut open the center "tube"
First put away the top and botom for other projects and then cut open the center "tube" along the glue line of the label. Cut straight from one end to the other to open up the tube.
Now you should have a self curling piece of clear PETE platic that will accomodate the pattern below.
Use grease pencil to draw the pattern and then cut it out with sizzors. You can use a hole punch or an ice pick to cut the small holes on the tabs that fit above and below the ears but be careful not to let it slip since PETE is awfully slippery.
Use paper clips and rubber bands or string to hold the shield in place and hop on your bike and head for the store to get a replacement bottle of soda!