As a draining and secretory system, the nasolacrimal ducts play a role in tear transport and non-specific immune defense. In this book recent advances about the nasolacrimal ducts have been summarized and discussed in context with nasolacrimal duct pathophysiology. 

and Questions.- 1.1 Introduction.- 1.2 Questions.- Materials and Methods.- 2.1 Human Material.- 2.2 Animal Material.- 2.3 Light Microscopy.- 2.4 Lectin Staining.- 2.5 Immunohistochemistry.- 2.6 Scanning Electron Microscopy.- 2.7 Transmission Electron Microscopy.- 2.8 Corrosion Vascular Casts.- 2.9 Reverse Transcription Polymerase Chain Reaction and Western Blot.- 2.10 Animal Investigations/Experiments.- Results.- 3.1 The Epithelium and the Underlying Lamina Propria of the Nasolacrimal Ducts.- 3.2 The Membranous Part of the Nasolacrimal Ducts.- 3.3 Absorption Experiments in the Nasolacrimal Ducts.- 3.4 Pathologic Findings in Dacryostenosis.- Discussion.- 4.1 Mechanisms of Immune Defence in the Nasolacrimal Ducts.- 4.2 Mechanisms Regulating Tear Flow Through the Nasolacrimal Ducts.- 4.3 Absorption of Tear Fluid Components.- 4.4 Insights into the Pathophysiology of Primary Acquired Dacryostenosis.- 4.5 Considerations on the Relationship Between Dry Eye and the Nasolacrimal Ducts.- Outlook..- Summary.- References.

The human nasolacrimal ducts are a borderland of both disciplines opthalmology and otorhinolaryngology which work closely together in the tretament of nasolacrimal disorders. The author summarizes recent advances about the nasolacrimal ducts and discusses them in a context with nasolacrimal duct pathophysiology. As a draining and secretory system  the nasolacrimal ducts play a role in tear transport and non-specific immune defense. Moreover, components of tear fluid are absorbed in the nasolacrimal passage and are transported into a surrounding vascular system. This system is comparable to a cavernous body which is subject to vegetative control. Organized mucosa-associated lymphoid tissue (MALT) is present in the nasolacrimal ducts displaying the cytomorphological and immunophenotypic features of MALT. The normally constant  absorption of tear fluid components into the blood vessels of the surrounding cavernous body  that are connected to the blood vessels of the outer eye could be a feedback signal for tear fluid production, which comes to a halt if these tear components are not absorbed. Thus, dry eye could be initiated. Defective stimulation of tear duct-associated lymphoid tissue could result in abnormal immune deviation at the ocular surface leading to an autoimmunological response that causes dry eye pathology. Moreover, malfunctions in the cavernous body and in its innervation may lead to disturbances in the tear outflow cycle, ocular congestions or total occlusion of the lacrimal passage. Based on the findings the pathomechanism of primary acquired dacryostenosis can be explained.