[Morphological alterations induced by preservatives in eye drops]

A large number of experimental and clinical investigations carried out recently have confirmed that the chronic application of eye drops induces significant cytological and histological impairment in ocular tissues. It is also generally accepted that preservatives are the components responsible for the observed changes. The most commonly used preservative in ophthalmology is benzalkonium chloride (BAC), which has a relatively high toxicity. Possible consequences of preservatives on the eye are chronic inflammation and subsequent fibrosis of the subconjunctiva and cell loss and structural changes in the conjunctival epithelium as well as in the epithelial and endothelial layers of the cornea. Frequently, dry eye symptoms occur or deteriorate during therapy. During the last few years new preservatives have been developed which seem to have fewer side effects; however, relatively little data are available with regard to these new substances. To minimize impairments of the eye, preservative-free formulations should be considered for therapy.