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Friedrich P Paulsen, Maximilian Zetzsche, Mohammad Javed Ali, Jens Heichel, Michael Scholz, Christian M. Hammer; New insight into tear transport through the upper and lower canaliculi of the nasolacrimal ducts. Invest. Ophthalmol. Vis. Sci. 2019;60(9):6382.
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© ARVO (1962-2015); The Authors (2016-present)
It is well-known that the function of Horner’s muscle is indispensable for the transport of “used” tears. However, it is as yet unclear how exactly the muscle fibers run and by which mechanisms they exert their functions. The present study was undertaken to obtain deeper insight into this matter.
Upper and lower canaliculi were dissected from body donors. Some of the specimens were prepared for scanning electron microscopy (SEM), others were sectioned for enzyme histochemistry (EHC) to investigate the distribution of slow and fast twitching muscle fibers in Horner’s muscle. SEM was performed to analyze the course of muscle fibers surrounding the canaliculi. One tear duct system was cut out en bloc after formalin fixation, serially sectioned and reconstructed using a newly developed technology for 3D reconstructionnamed HiDi®. Patients that had undergone dacryocystorhinostomy (DCR) were video-analyzed from the nose during active blinking, focusing on viewing the temporal wall of the lacrimal sac where the canaliculi penetrated the lacrimal sac.
SEM revealed that the muscle fibers of Horner’s muscle surrounded the vertical part of each canaliculus in a scissor like pattern whereas they ran in parallel to the first two thirds of the horizontal parts surrounding the respective canaliculus. Here, the muscle fibers were embedded in dense connective tissue forming a special fibromuscular network. At the nasal third, muscle fibers left the canaliculi and ran to the posterior part of the fascia of the sac and to the lacrimal bone. EHC revealed that Horner’s muscle contained nearly an equal distribution of type I and type IIB muscle fibers. 3D reconstruction supported the SEM data. Endonasal videoanalysis of patients after DCR with a nasally open lacrimal sac revealed bulging of the temporal wall of the lacrimal sac during blinking.
The results support the hypothesis that contraction of Horner’s muscle leads to opening of the canaliculi. Presumably, this is the result of the special arrangement of muscle and connective tissue fibers. Dilatation of the posterior part of the nasal wall of the lacrimal sac leads to a suction mechanism removing “used” tear fluid from the lacus lacrimalis at the ocular surface through the lacrimal puncta and canaliculi into the lacrimal sac. The mix of fast contracting and fatigue resistant muscle fibers is ideally suited for the blink mechanism.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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