Lacrimal scintigraphy (LS) was performed on asymptomatic lacrimal drainage systems and the results were evaluated to understand the physiology of lacrimal drainage. It was found that a physiological obstruction can exist at the level of the nasolacrimal duct in normal asymptomatic individuals, and it is suggested that this obstruction is due to the resistance offered by the valve of Hasner, which in turn is dependent on (a) the volume of fluid in the lacrimal sac and the nasolacrimal duct, and (b) the anatomical integrity of the valve. The LS observations are taken into account to postulate a mechanism of drainage from the lacrimal sac into the nose, which hitherto has not been very clear. It is also suggested that reflux can occur between the various compartments of the lacrimal drainage system and that the various valves in the membranous passageway can become incompetent in an obstructed system.
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