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The nasolacrimal duct (NLD) is the terminal part of the nasolacrimal apparatus.
intraosseous part (12 mm): enters the lacrimal groove and descends within the nasolacrimal canal of the maxilla
membranous part (5 mm): runs in the nasal mucosa; terminates below the inferior nasal meatus as a slit-like opening where it is covered by a mucosal fold called the valve of Hasner (or plica lacrimalis)
Up to eight 'valves' of the nasolacrimal duct have been defined in the literature and are commonly seen in older anatomical texts and monographs. However, it has been contended that some of these are not true mucosal valves but just embryological irregularities in the ductal wall. From craniad to caudad, these 'valves' have been named: Foltz, Bochdalek, Rosenmüller, Huschke, Aubaret, Krause (or Béraud), Taillefer, Hasner (or Cruveilhier/Bianchi) 3,4
The valves of Bochdalek and Foltz are located within the lacrimal puncta, the valves of Rosenmuller and Huschke control the ostium of canaliculi to the lacrimal sac, the valve of Krause guards the path where the lacrimal sac enters the nasolacrimal duct, and the valve of Teileffer is located in the central lacrimal duct 5.
Therefore a recent retrospective study used digital subtraction dacryocystography (a high spatial resolution technique) to precisely define the intraluminal anatomy of the nasolacrimal duct and determine which of these named structures really represent consistent anatomical features. The researchers used a study group of 92 individuals for whom DS-DCG had previously been reported as normal 3,4:
The inferior group of 'valves' were consistently better seen:
valve of Krause: was visible in 79.3% cases
valve of Taillefer: 93.5% cases
valve of Hasner (plica lacrimalis): 98.9% cases
The superior group of 'valves' were inconsistently visualized and were therefore thought to be mucosal irregularities rather than true anatomical valves:
valve of Foltz and valve of Bochdalek: were visible in 17.1% cases
valve of Rosenmüller and valve of Huschke: 46.4% cases
valve of Aubaret: 40% cases