I have this situation also. The tear glands (tear ducts only carry the tears to the eye)are underactive, producing only enough tears to keep the eyes lubricated,severely in one eye. The problem with this situation is the inability to wash out eye irritants. I get pink eye if anyone in my reach has it! The driest eye is actually now smaller than the other from the frequent infections. I'll never be able to wear contacts, or have laser surgery. I put sterile natural tears drops in my eyes often, especially when the weather is dry, or there is a lot of pollen in the air. It is also important to keep your son hydrated so that the eye isn't also dry from the inside. If he takes any allergy medicine in the future, the hydration will be even more important.
If you have a PPO insurance plan, I would take him to a pediatric eye specialist. They'll tell you the same thing that I have, but will then be able to record base line data and be able to note changes in the future.