Some manufacturers claim that their eye drops can be used as often as you like. If you are using lubricating eye drops more than once every four hours, this is a sign that the drops alone are not alleviating or treating your symptoms. Other co-morbidities, in addition to aqueous deficient Dry Eye, may be present.
If you are using them more than 4-6 times per day, even preservative-free lubricating drops are not completely safe to use as often as you like,