Physiology of Lacrimal Drainage
There are many factors contributing to lacrimal elimination, but the most important mechanism is canalicular and sac pump mechanism. Canalicular pump is probably more important than the sac pump because following DCR, tears are still drained through the c
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Ali Riza Cenk Çelebi and T. Metin Önerci
Keywords
Lacrimal pump system • Krehbiel’s effect • Bernoulli principle • Microciliation • Siphon effect • Capillarity
Core Messages
• There are many factors contributing to lacrimal elimination, but the most important mechanism is canalicular and sac pump mechanism. • Canalicular pump is probably more important than the sac pump because following DCR, tears are still drained through the canaliculi to the nose. • The pressure gradient between the canaliculi and the sac cannot be produced if the canaliculus is slit open. Therefore, the lacrimal canaliculi should be preserved and should not be damaged.
A.R.C. Çelebi, MD (*) Ophthalmology Clinic, Niğde State Hospital, Feridun Zeren Street, Niğde 51000, Turkey e-mail: [email protected] T.M. Önerci, MD Department of Otorhinolaryngology, Faculty of Medicine, Hacettepe University, Ankara, Turkey
• Tear elimination is equivalent through the upper and lower canalicular systems. Therefore, attention should be given not to damage both the upper and lower canaliculus.
The lacrimal drainage system works to remove those tears secreted into the palpebral aperture to cover the cornea at a rate of 1.2 μl/min with a total 24-h secretory volume of approximately 10 ml (Hurwitz 1996). The tear film travels across the surface of the globe and eyelids, enters the puncta/ ampulla, passes through the canaliculi, and enters the lacrimal sac/nasolacrimal duct/nasal passages. With blinking (orbicularis muscle contraction), the closure of palpebral aperture starts from lateral and proceeds to medial. This action propels the tears medially toward the lacrimal lake (Hurwitz 1996). Factors contributing to lacrimal elimination may include: • Evaporation of tears from the ocular surface • Capillary attraction of the tears • Reservoir drainage into the lacrimal sac (socalled Krehbiel flow) • Siphon effect • Microciliation and absorption of tears by the lacrimal sac mucosa
T.M. Önerci (ed.), Nasal Physiology and Pathophysiology of Nasal Disorders, DOI 10.1007/978-3-642-37250-6_16, © Springer-Verlag Berlin Heidelberg 2013
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A.R.C. Çelebi and T.M. Önerci
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• Bernoulli’s principle and Venturi tube effect • Physical forces such as gravity • Canalicular and sac pump mechanism
16.1
Factors in Tear Flow
is discharged at a level lower than the surface of the reservoir. It is important that while the siphon must touch the liquid in the (upper) reservoir (the surface of the liquid must be above the intake opening), it need not touch the liquid in the lower reservoir and indeed there need not be a lower reservoir – liquid can discharge into midair.
16.1.1 Evaporation Much of the tears is lost by direct evaporation from the ocular surface. Low humidity and wind increase this loss. According to Schirmer almost half of the secreted tears were lost by evaporation (Hurwitz 1996).
16.1.2 Capillarity Capillarity or capillary action is the ability of a liquid to flow in a narrow tube without assistance of gravity. This effect can be seen in the dra
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