Purpose of review: The purpose of the present review is to examine the hypersensitivity reactions to preservatives in topical ophthalmic therapies.
Recent findings: Ocular hypersensitivity reactions to different types of preservatives in different chemical classes of topical ophthalmic treatments reviewed in the literature include IgE-mast cell mediated, cell mediated and toxic. Quaternary ammoniums (benzalkonium chloride) are most commonly (8% reported cases in OVID and PubMED based searches) associated with irritant toxic reactions whereas the organomercurials (thimerosal) and the alcohols (chlorobutanol) have the highest association (19% of OVID and 14% of PubMED based searches and 20% of OVID and 11% of PubMED searches), respectively, with allergic responses although the term allergy for the 'alcohols' appears to be actually an irritant effect whereas the organomercurials appear to truly interact with the immune system as neoantigens.
Summary: A large number of clinical and experimental studies reveal that preservatives in topical ophthalmic medications have been demonstrated to produce effects from inflammation/ hypersensitivity to permanent cytotoxic effects involving all structures of the eye.