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The excretory system is made up of the lacrimal puncta, the lacrimal canals, the lacrimal sac, the nasolacrimal duct and the nasal cavity. It is estimated that under normal conditions, over 90% of the lacrimal fluid is removed by the excretory system – the remaining fluid evaporates between blinks. Blinking has a vital role in tear drainage. Contraction of the orbicularis muscle during blinking causes alternate positive and negative pressures in the lacrimal sac, forming the lacrimal ‘pump’ which facilitates the drainage of excess lacrimal fluid.
Drainage of tears through the puncta, into the lacrimal sac and then into the nasal cavity takes place in a sequence of steps:
Normal Tear Flow
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