What Causes Pain In The Eyes?

I am actually asking this question for one of my sons who is experiencing aching in both eyes, sometimes there is muscle agitation, and he also may feel some warmth at times in those eyes. He seemed to think it might be related to working too long on the computer because at times it does seem to subside. He has gone to two different opthamologists in the last six months, gotten new eye glass lenses, had eye drops. Most recently, he has had a CAT scan which was negative; tomorrow he is going in for an MRI; he has had blood work this week, awaiting the results of that. He is not overweight and exercises almost daily lifting weights, treadmill, etc. He does have asthma and I was thinking perhaps it was connected to the meds he takes for that. I did look up the side effects of albuterol because I know he has been on that in the past. Not certain what his prescription of the inhaler is at this time, however. I appreciate any input you may have. Patricia