tear pumping

tear pumping 

The mechanism involving blinking, which acts to bring fresh tears with oxygen and nutrients to the cornea behind a contact lens, and pumping stale tears containing carbon dioxide, lactic acid and other waste products from beneath the lens. It occurs most readily with hard contact lenses (between 14% and 20% of the tear volume is exchanged with each blink) and to a much smaller extent with soft lenses (between 1% and 5% of the tear volume is exchanged with each blink). See hypoxia; oxygen transmissibility.

Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann