Dogs can get conjunctivitis also airbourne allergies and irritants that float through the air eg smoke pollen sprays. Sand in the eyes also can hurt eyes. Get your vet to inspect them. Be extremely careful as far as what you put in the eyes to clean them. Dont rub. Wash them & wipe with a warm wet flannel from the inner corner outwards gently & apply drops from vet once diagnosed. If its an irritant not an infection you can find recipes on google for natural eye washes for dogs like chamomile or colloidial silver could help. Also make sure your dogs eyes arent being exposed to high heat eg fireplace oven as it can dry the eyes & cause excessive tearyness as the eye overcompensates.Make sure you dont spray hairspray perfume or deoderant on when your dogs standing close looking up. Dont smoke ciggys near your dog if your a smoker.