1Schaudig U., 2Paulsen F., 3Thale A.

1Augenklinik und Poliklinik, Universitäts-Klinikum-Eppendorf, Martinistrasse 52, 20246 Hamburg; 2Institut für Anatomie, Christian Albrechts Universität , Olshausenstrasse 40, 24098 Kiel; 3Augenklinik, Christian Albrechts Universität, Hegewischstrasse 2, 24105 Kiel

Despite a variety of theories, the mechanisms of tear drainage through the efferent tear ways is still incompletely understood. The possible influence of a well known vascular plexus around the tear sac and the nasolacrimal duct has long been underestimated. New investigations about the structure of this cavernous body show its potential in tear transportation: in electronmicroscopical investigations, barrier arteries, capacitance veins and throttle veins are found that regulate arterial inflow and venous outflow, thus regulating the filling of the cavernous body and the diameter of the tear way lumen. The presence of a regulatory neuronal network has been demonstrated by neuronal markers (NSE) and different neuropeptides (substance p, neuropeptide y, a.o.). The function of the epithelial lining of the efferent tearways has only recently been studied in detail. A variety of specific and unspecific antimicrobial defense mechanisms have been found. The superficial epithelial cells and seromucinous glands in the tear sac produce the antimicrobial peptide lysozyme, lactoferrin and phospholipase A2 (PLA2). Lysozyme cracks glycoside connections in the cell wall of gram-positive bacteria and enhances the antibacterial effect of complement and t-cells against gram-negative organisms. Iron-binding lactoferrin reduces the amount of free iron available for bacteria and has bacteriostatic as well as bacteriocidal effects. Calcium-dependent secretory PLA2 has been shown to be an important factor of the antimicrobial defense of the tear fluid against grampositive organisms and seems to act accordingly within the efferent tear way system. Thus, the tearway epithelium is equipped with antimicrobial defense mechanisms similar to those of the intestinal mucosa, including a recently detected specific immunologic defense system. This tearduct-associated lymphoid tissue, named "TALT", and the regulatory mechanisms of antimicrobial defense in the epithelium are currently under close investigation.

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