Neuroanatomy of the Normal Lacrimal Drainage System: Paper I: Histopathological, Immunohistochemical and Electron Microscopic Characterization.

PURPOSE: To investigate and map the neuroanatomy of the lacrimal drainage system (LDS).

METHODS

A prospective study was performed on 10 samples of the canaliculi, the lacrimal sac, and the nasolacrimal duct. Samples were obtained from either fresh cadavers or from exenterated specimens with healthy LDS. Assessment was performed using techniques of histopathology, immunohistochemistry, double immunofluorescence, Western blot, and scanning electron microscopy. Special stains used were Masson's trichrome, Luxol fast blue, and Kulchitsky-Pal. Neural markers used were beta-Tubulin III (TUJ-1), protein gene product 9.5, glial fibrillary acidic protein, neuron-specific enolase, S-100, microtubule-associated protein 2, vesicular monoamine transporter 2, dopamine beta-hydroxylase, tyrosine hydroxylase, neurofilament H, and neuronal nitric oxide synthase. The neural structures within the LDS were categorized based on their morphology, topohistology, and the level of their presence within the tissues. Scanning electron microscopy was used to further delineate the tissue innervation.

RESULTS

There were distinct neurotopographical features across different anatomical regions of the LDS. The epithelial, subepithelial, and superficial stromal regions were predominantly innervated by thinner neurons, while the deep stromal and subfascial regions demonstrated thick nerve bundles. There was a mix of myelinated and unmyelinated nerve fibers, with the former predominating. The frequency and distribution of the vasa nervorum and periglandular innervation significantly increased in the nasolacrimal duct when compared with proximal drainage structures. The epithelial and subepithelial regions of the lacrimal sac predominantly expressed microtubule-associated protein 2 and vesicular monoamine transporter 2, while those of the nasolacrimal duct expressed dopamine beta-hydroxylase and tyrosine hydroxylase, reflecting the increasing influence of the autonomic nervous system on the glands and blood vessels of the nasolacrimal duct. Topographical mapping of the neuroanatomy provided insights into the differential innervation of the LDS.

CONCLUSION

This is the first focused study to delineate the tissue innervation of the LDS. The neuroanatomical assessment of the LDS demonstrates a rich and diverse neural supply across its anatomical structures, with characteristic histological levels of tissue innervation possibly reflecting complex neural regulation.