Nonspecific defense mechanisms of the eye

It has long been recognized that important nonspecific defense mechanisms protect the eye from the multitudinous microbial insults to which it is subjected in the course of everyday life. It is also well known that the tears, with their ability to flush airborne and other microbes into the nose, are largely responsible for this protection. Ophthalmologists have long known that any interference with lacrimal drainage, or a lack of tears for any reason, predispose the external eye, particularly the conjunctiva and cornea, to infection. In all, there are three defense mechanisms for the eye: (1) the protection afforded by the skin and mucous membranes; (2) the acute inflammatory reaction; and (3) the development of specific humoral or cellular immunity. The first two are nonspecific and the principal subjects of this review.