7 By Daria Zaitseva The Science of Tears 淚之科學 Ever cried when watching a movie, chopping onions, or when dirt gets in your eye? The tears rolling down aren’t just saline: They're a sophisticated biological fluid safeguarding your eyes, which contain metabolites, electrolytes, glucose, oxygen, and up to 1,500 proteins, including the most abundant ones associated with anti-inflammatory and antibacterial activity [1, 2]. Tears play a vital role in protecting and lubricating the eye surface. They can even offer insights about your health. Now let’s unpack the science of tears! What Makes a Tear? First of all, tears can be classified into three types. “Basal tears” are for housekeeping purposes to keep the eye protected and lubricated all the time. Our eye also secretes “reflex tears” in response to irritants like dust or smoke, and “emotional tears” in response to strong emotions like sadness, anger, and joy [1]. Some scientists suspected that emotional tears could provide an emotional relief based on the discovery that additional proteins and hormones were detected, but current evidence remains inconclusive to this hypothesis [3]. Have you wondered why tears can stay on the eye surface? A thin layer of tear fluid called “tear film” is evenly spread on the eye surface every time we blink. The tear film turns out to be not just a layer of aqueous liquid; it consists of an inner mucin layer, a middle aqueous layer, and an outer lipid layer [1]. The inner mucin layer anchors the middle aqueous layer to the hydrophobic corneal surface. The aqueous layer is crucial for lubricating and protecting the eye surface by flushing away toxins and debris.
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