Anatomical and Functional Alterations in Nasolacrimal Duct Obstruction: A Comprehensive Review.

The lacrimal drainage system, or LDS, is an intricate anatomical and functional system that mobilizes and drains tears from the ocular surface into the nasal cavity. The drainage system first begins at the puncta, small openings located at the medial eyelids which actively funnel tears into the canaliculi. The canaliculi drain into the lacrimal sac (LS), with the LS residing in the lacrimal fossa, which collects the tear fluid and subsequently drains the fluid into the nasolacrimal duct (NLD), which empties into the inferior meatus of the nasal cavity. Variations in canalicular length and duct curvature and diameters influence the dynamics of tear flow in the LDS as well as the potential for obstruction. It should be noted that females appear to have narrower NLDs, which could contribute to the higher rates observed for nasolacrimal duct obstruction (NLDO). Importantly, the lacrimal pump mechanism activates during blinking by the Horner-Duverney part of the orbicularis oculi muscle on each side. There are valves in the LDS, like the valve of Rosenmüller, that allow unidirectional flow and prevent anterograde flow from the NLD into the inferior meatus nasal or pharyngeal region. An obstruction to the flow of tears out of the lacrimal drainage system could cause secondary changes in the lacrimal gland (LG), such as altered protein secretion properties, histologic remodeling in the LG, or altered migration of immune cells. The inflammatory and fibrotic processes involved in the progression of NLDO are likely mediated by T and B lymphocytes and fibrogenic cytokines that create fibroblasts which leads to progressive narrowing of the ductal lumen by various inflammatory and fibrotic processes such as lap-time would reveal. Anatomical influences related to NLDO include canalicular stenosis, dacryocystocele, deviated nasal septum (DNS), inferior turbinate hypertrophy (ITH), and sinus pathology. Diagnosis of NLDO is made through a clinical examination with imaging studies, including computed tomography (CT) or dacryocystography (DCG), and functional studies. Treatment includes conservative therapy, probing, balloon dacryoplasty, and dacryocystorhinostomy (DCR); outcomes are multifactorial, including etiology, age, and comorbidity.