title: Tear flow dynamics in the human nasolacrimal ducts--a pilot study using dynamic magnetic resonance imaging.
abstract: BACKGROUND
  Jones's theory of tear drainage suggests that the lacrimal sac fills when the eyelids are closed and empties into the nasolacrimal duct when the eyelids are open. This is aided by the contraction of the orbicularis muscle during each blink. This study was undertaken to ascertain the possibility of seeing the dynamic movement of tears in the nasolacrimal system during blinks using magnetic resonance dacryocystography (MR-DCG).
  
  
  METHODS
  The sac was initially localized with a three-plane gradient echo sequence using a 1.5-T MRI platform. Fast, dynamic MR-DCG was carried out after we had instilled topically balanced salt solution (BSS) in five subjects and 0.5% gadolinium in seven subjects. The volunteers were asked to close and open their eyes during the fast imaging. The images were digitized to enable us to see the actual movement of fluid in the system.
  
  
  RESULTS
  The tear movement was clearly seen as a bolus in the volunteers where BSS was used. The fluid passed into the nasolacrimal duct after several blinks when patent. The sac was never seen to empty completely. Though differential filling was seen between the upper and lower part of the sac, it was difficult to see the actual fluid movement in the volunteers when topical gadolinium was used.
  
  
  CONCLUSIONS
  The findings of the study are supportive of the notion of fluid travel in the form of a bolus through the sac. Once a threshold volume is reached in the lower end of the sac, the fluid is seen to pass through the nasolacrimal duct. This happens after several blinks.
authors.affiliation: The Eye Institute, National University Hospital, Singapore. ophv14@nus.edu.sg
authors.forename: Shantha
authors.initials: S
authors.lastname: Amrith
authors.forename: Poh Sun
authors.initials: PS
authors.lastname: Goh
authors.forename: Shih-Chang
authors.initials: SC
authors.lastname: Wang
mesh_terms: D000085:Acetates / Q000008:administration & dosage; D001767:Blinking / Q000502:physiology; D003287:Contrast Media; D004338:Drug Combinations; D005143:Eyelids / Q000502:physiology; D005682:Gadolinium; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008903:Minerals / Q000008:administration & dosage; D009301:Nasolacrimal Duct / Q000000981:diagnostic imaging / Q000378:metabolism*; D009801:Oculomotor Muscles / Q000502:physiology; D010865:Pilot Projects; D011859:Radiography; D012965:Sodium Chloride / Q000008:administration & dosage; D013666:Tears / Q000378:metabolism*
chemical_list: D000085:Acetates; C030660:BSS solution; D003287:Contrast Media; D004338:Drug Combinations; D008903:Minerals; D012965:Sodium Chloride; D005682:Gadolinium
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