The effects of drugs on tear flow.

Systemic administration of drugs can diminish the tear flow as with timolol and atropine, or can increase the tear production as with bromhexine. Turpentine fumes (100 ppm/30 min or 30 ppm/8 h) have been shown to diminish the break up time (BUT) of tears by diminishing the lipid layer of the precorneal film. Ointment and drugs suspended in oil also diminish BUT, not only do they dry the corneal and conjunctival epithelium (judged by the rose bengal score) but also diminish the outflow as judged by the tear river dye dilution test in both normal people and those with keratoconjunctivitis sicca. Benzalconium chloride in concentrations used as a preservative and cocaine have also been shown to reduce BUT.