Side effects of antiglaucomatous drugs on the ocular surface.

An increasing number of studies, both experimental and epidemiologic, have shown that filtering glaucoma surgery has progressively become less effective than initially described. Of a number of risk factors for failure, duration and number of antiglaucoma drugs before surgery seem to play a critical role, and high accumulated antiglaucoma topical treatments significantly reduce success rates. Histopathologic studies have confirmed that topically applied drugs may exert toxic effects to the corneoconjunctival surface and induce chronic infraclinical inflammation, as shown by the presence of immunologic changes and inflammatory infiltrates in multitreated eyes. The origin of topical inflammation has not yet been clearly determined, but benzalkonium chloride, which is used as a preservative in almost all antiglaucoma preparations, has shown strong evidence of toxicity to the ocular surface. A number of questions remain to be investigated, but suppression of preservatives from chronically applied drugs should be a critical issue in the near future.