19 Benzalkonium Chloride and Outflow Resistance Benzalkonium chloride (BAK), a quaternary ammonium detergent, has been the most common preservative in glaucoma drops. Increasing research interest in BAK and its effect on the ocular surface and conjunctiva has shown detrimental effects of BAK on corneal and conjunctival epithelial cells, trabecular meshwork cells, and corneal nerves.1 BAK activates conjunctival fibroblasts, mobilizes inflammatory cells, damages goblet cells, and may enhance subconjunctival fibrosis.2 Glaucoma filtration surgery aims to optimize aqueous outflow. Chronic antiglaucoma medications may contribute to trabeculectomy failure,3 as may BAK in a dose–response manner.4 Many glaucoma patients instill multiple antiglaucoma drops with inevitable additive BAK doses; each product with BAK has doses between 0.004% and 0.02%. By the time trabeculectomy surgery is indicated, we may have created an environment for surgical failure. Anecdotally, higher doses of mitomycin and greater numbers of 5-fluorouracil injections may be necessary for success, with attendant increases in complications. Less toxic preservatives such as Purite, SofZia, and Polyquad have been used increasingly, along with unpreserved eyedrops. We need research to determine how these options affect trabeculectomy success.
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