Pathophysiological Aspects of PANDO, Dacryolithiasis, Dry Eye, and Punctum Plugs

2.6 Conclusions

As described, the human nasolacrimal ducts must be included in the considerations concerning dry eye. Areas of interest include analyses of normal tear components, such as mucins, TFF peptides, and freely water-soluble small molecules (e.g., urea or amino acids), or perhaps smaller molecular tear proteins such as lysozyme. Moreover, analysis of such molecules in certain diseases, such as dacryostenosis, are of interest. Such investigations would be useful for extrapolation to the human situation, as the exact mechanism of absorption and regulation of these processes at the mucosa of the lacrimal passage is still not understood. Current investigations of epithelial transporter systems of the human nasolacrimal ducts will give deeper insights into possible routes of absorption and also the substances that are able to be absorbed. Possibly, some of these transporters are regulated by hormones in the efferent tear ducts, similar to the action of the water transporter aquaporine (AQP) 2 in the kidney, where AQP 2 is only present in the apical membrane of collecting duct main cells under the influence of adiuretic hormone. Moreover, current analysis of TALT and also conjunctiva-associated lymphoid tissue (CALT), as well as different epithelial cells of the lacrimal passage, are interesting with regard to the induction of tolerance in the nasolacrimal system and at the ocular surface.