Could be a couple of things Carla.
Is he drinking enough? (Water)
What's his caffine intake?
What are his sleep patterns like?
Working at a VDU?
Does he/ or should he wear glasses? (If he doesn't know, have a quick look at the family line, do any of them?)
Is he eating properly? (Our eating patterns can really put our bodies out of sync).
Does he have hayfever? (Weird one this but because of the mild winter we're experiencing some people are having symptons of hayfever and getting it confused with other things as they're not expecting it).
Or (as highlighted by Battersby) a history of sinus problems?
If he's not drinking more than 8 glasses of water a day then he should. If he drinks a lot of caffine, cut down. If his sleep patterns are bad then he needs to alter them (those SAD boxes are supposed to be good). VDU usage, every twenty minutes take your eyes off the screen (occy health departments can advise on this). A check up at the opticians even if he doesn't seem to need glasses (unless he has been within six months) wouldn't go amiss. Make sure he's getting five a day and not eating too much rubbish. If possible hayfever then treat as he would in summer. Sinus's Battersby covered.
But as always, if in doubt, visit the quack.