Has he been to see an optometrist? I ask, because he isn't too young. And anything specifically with his eyes, I think it is best to go to an optometrist first off. My personal thoughts are this: Perhaps he is squinting his eyes in order to clear up his vision - squinting makes my eyes water, but because I am nearsighted, it also helps clear up my vision... If he hasn't been to see an optometrist, that would be my suggestion. My son has been wearing glasses since preschool. One day, prior to glasses and prior to him ever going to an optometrist, he was watching the purple dinosaur on TV. They were showing a blurry screen, which depicted how a child who needed glasses sees the world. Luckily, I was standing right there, because my son told me "Mommy, that's how I see!". Wow. I took him to my optometrist's office, and sure enough! He was sorely in need of glasses! (And his pediatrician's simple eye exams never caught this) Once my son got his glasses, he was a new child! He had been very quiet and kept to himself at preschool - but once he had glasses he became very confident of himself and now is very outgoing and friendly.
I hope this has helped somewhat. Best of luck to you and your son!