Neurogenic inflammation: a first line of defense for the ocular surface.

Neurogenic inflammation and innate immunity may work together to protect mucosal surfaces, including the ocular surface. When the eye is exposed to pathogens, chemical irritants, or mechanical disruption, neurogenic inflammation is produced through release of neuromodulators, such as substance P and calcitonin gene-related peptide. This leads to the breakdown of the blood-tissue barrier, edema, and release of polymorphonuclear leukocytes into the tears, thus allowing intervention of systemic immunity. Neurogenic mechanisms may have a significant role in the onset and chronicity of ocular surface inflammation in conditions such as dry eye.