Because tears, like any of the secretions of our body, have a raison d'être: they fulfill the delicate function of protecting the eyes, keeping the surface of the cornea transparent, moist and clean.
What Causes Crying? Tears are the secretion of the lacrimal glands. The largest of these glands are in the upper outer corner of the orbit of the eye; but there are smaller ones, scattered on the inside of the eyelids.
• When the blinking movements are made or when the eyelids are tightened, the secretion of the glands increases, then the tears come out through the so-called tear points or tiny pores that open in the vicinity of the inner angle of the eye, on the edge of the eyelid and through the nasolacrimal ducts, which flow into the cavities of the nose.
• Tear fluid flows continuously in order to keep the eye well lubricated.
• But, if any stimulus causes it to flow in abundance, the tears come out of the eyelids. This requires special conditions.
• Tears come from strong emotions, feelings of pain and anger, convulsive laughter (sometimes crying and laughing at the same time), watching for a long time a flame, a lamp or any other source of light or very intense heat, the introduction of a foreign body into the eye, rapid movement of the eyelids, tightening one eyelid against the other and many other circumstances, which would be long to describe.
• The aqueous liquid that forms a tear contains several salts (but not in excessive amounts), especially sodium chloride (common salt) in addition to small amounts of proteins, glucose and a special substance called lysozyme, which is an amino acid with power to destroy bacteria and microorganisms that can penetrate between the eyelids, the cornea or the conjunctiva of the eye.
• The daily secretion of tears, under normal conditions, is calculated in one or two cubic centimeters. The fluid is poured through six to ten excretory ducts located in the orbit and in the thickness of the upper eyelid.