Blinking and the mechanics of the lacrimal drainage system.

High-speed photography, using picture rates up to 500/sec, has confirmed many key aspects of the tear drainage process reported over the years by various investigators. The punctal openings are seen to elevate themselves from the lid margin at the start of the closing phase of the blink, allowing their forceful meeting and occlusion by the time the closing lid is halfway down. Completion of lid closure then compresses the canaliculi and lacrimal sac, forcing contained fluid through the drainage system. The elastic expansion of the channels during the opening phase of the blink forms a suction, holding the lid margins at the punctal region together as the lids open. During the latter part of this opening, the punctal areas are seen to "pop' apart suddenly as the vacuum is broken, and tear fluid from the marginal tear strips is drawn into the puncta in the first few seconds following the blink.