Clearly one answer to this is: wear glasses.
Another answer would be: the worst thing is when you crash because there's a fly in your eye.
This is the worst year I've experienced for both breathing flies in and getting the critters lodged in one or other eye. I can't get comfortable wearing glasses, I don't even wear sunglasses. It seems that even the most firmly wedged fly washes out by itself after a short while, but is there any health risk to the fly being in there? Will I die? - Talking about UK local flies, not those funny-talking foreign flies.