I am far sighted in one eye and VERY near sighted in the other. So there's a lot of close up stuff i don't see unless i REALLY get in close. i sat down close to my bike a couple months ago and to my horror i saw lots of tiny slits in the tire.
I searched the complete tire and found that there was tiny pieces of glass in some of the slits. I worked all the glass out carefully, and then I moved on to Raleighdon's bike with the great Continentals on it. His ALSO had those slits, I found one piece of debris in it.
It pays to inspect the tires carefully. I don't see how you can avoid glass in this country where people love to throw everything out their windows!