Ocular surface defense mechanisms.

The outer eye is furnished with a variety of defenses active in protecting against continual exposure to the hazards. These defenses include the bony orbit, the eyelids and cilia, the tear film, corneal and conjunctival epithelium, and a submucosal secretory immunoglobulin system. Compromise of one or more of these components in disease states can lead to ocular infection. Rapid engulfment of foreign material introduced into the tearfilm is demonstrated with the use of polystyrene microspheres.