sometimes that happens to my dogs if they are looking for downed birds in alkalli bullrush.
what I think you have ....
There is a weed out there that I do not know the name of. It looks like a little black flower when it touches something it has like tiny spring loaded fork shaped burs that stick in your neoprene waders, levis, dogs coat, and even their eyes. The bad thing about it is the burs are barbed.if they get in the eyes the tiny prongs of the "fork" break off causing some real eye problems. My vet called it "micro-bur" but i think that is a name he made up. they can get it out no problem....they see it all the time.
sometimes they will work themselves out, but they can cause perminent damage if left in.
some dogs seem to be more prone to it than others.