Preservative-free (PF) formulations - Preservative intolerance should be diagnosed by an ophthalmologist. If PF formulation is warranted, proprietary preservative-free formulations (often available as unit dose preparations) should be prescribed if at all possible. Manufactured “specials” are unlicensed and almost invariably cost significantly more.  PF formulations are appropriate, for example when a patient wears soft contact lenses or daily disposable contact lenses and wearing glasses instead is not a viable option such as for long courses OR where patient shows signs of preservative toxicity sometimes seen with multiple daily administrations.