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Debbasch C., Pisella P. J.
Long term use of antiglaucoma drugs has been associated with toxic as well as inflammatory changes of the ocular surface whereas success rates of filtration surgery directly depends on the integrity of the conjunctiva. In vitro and in vivo experiments on antiglaucomatous drugs have clearly demonstrated that at least a part of their adverse effects may be related to preservative, specially benzalkonium chloride (BAC), the most commonly used preservative in many available ophthalmic solutions. In the eye, preservative turnover is very slow and quaternary ammonium molecules can be retained in ocular tissues up to 7 days. Three types of toxicity mechanisms have been described: detergent effects causing loss of tear film stability, direct toxic effects to the corneal and conjunctival epithelia, and immunoallergic reactions. Preservatives decrease the stability of the precorneal tear film with increased evaporation, directly, owing to their surfactant properties and detergent effect on the lipid layer, and indirectly by decreasing the number of mucous cells in the conjunctival epithelium.