Lab pup with tearing eyes

I just found this forum and it has so much helpful information At Christmas my son gave me a yellow male lab he was born Oct 2008 since we have had him his eyes have watered and he has tear stains when I had his shots the vet checked his eyes and said they were clear and he had no eyelash problems the vet figured that his tear ducks were clogged and would clean them out when we had him neutered since I'm not getting him neutered until he is at least a year old I have been doing alot of research on the internet and am now wondering if he just might have a food allergy He has been on the same food that the breeder started him on Purina Large Breed Puppy Chow after reading the ingredents I see that it does contain corn etc I would like to change his food to see if this is the cause of his eye problem Would anyone have any suggestions as to what type of food or a homemade puppy food recipe that I can give him? Also should I just stop the Purina all at once or should I mix it in with the other kind and gradually take him off the Purina? Other than the eye tearing he is doing great on the Purina He is very strong, lean, healthy, very energetic Also would anyone have a good tear stain removal remedy I'm not much into chemical remedy's and would prefer something that is holistic or herbal if possible
Thanks
Sandy