Tears are raining, where do they come from? To cry, why are there no tears? Crystal tears, just because of sadness and pain? Even Lin Daiyu, who shed a lifetime of lovesick tears, her tears, like those of ordinary people, are an important part of the eye protection mechanism. Tears nourish and moisten the cornea, lubricate the movement of the eyelids and eyeballs, flush dust and microorganisms from the surface of the cornea and conjunctiva, and play a role in antibacterial, oxygenation, and maintenance of the normal optical plane of the cornea. Where is the source of the river of tears? The lacrimal glands, paracrine glands, and conjunctival cupped cells are the diagrams that secrete tears. The lacrimal glands are located in the lacrimal fossa in the upper outer corner of the eye. The paracrine lacrimal glands include the Krause’s gland, Wolfring’s gland, and Ciaccio’s gland. Histologically, the lacrimal gland is a chylomicronous plasma gland formed by the merging of glandular lobules the size of a pinpoint eye. The cupular cells are distributed in the conjunctiva. Tears are derived from basal and reflex secretion. Basal secretion remains present during sleep, mucus is secreted by cupula cells, Henle’s crypt, and non-cupula cells of the lacrimal gland, aqueous humor is secreted by Krause’s gland, Wolfring’s gland, and lipids are obtained from the lacrimal gland, Zeis’ gland, and Moll’s gland. Reflex secretion is secreted by the lacrimal glands, including peripheral sensory reflex secretion, retinal reflex secretion, and mental reflex secretion. Tears are often referred to as “bitter tears”, but in fact they are a weakly alkaline, clear liquid with a pH of 7.1-7.8. 98.2% of tears are water, except for a small amount of inorganic salts and proteins, and also contain lysozyme, immunoglobulin A, complement system, b-solubilins, lactoferrin, etc. These components are very important for These ingredients are very important for antibacterial and anti-inflammatory. In a normal waking state, people secrete 0.5-0.6ml of tears in 16 hours, 0.9-2.2ul per minute. 7-10ul of tears in the normal conjunctival sac. with normal quality and quantity of tears, you will have clear, bright eyes. Where do the tears that are secreted go? Most of the tears disappear through evaporation and some are discharged through the outflow channels. The tear duct includes the upper and lower tear dots, tear ductlets, common tear duct, tear sac and nasolacrimal duct figure. What are the causes of tearfulness? There are two possible causes of tearing: excessive secretion of tears when the eye is irritated or emotionally excited, and obstruction of drainage due to poor lacrimal passage. If the secretion exceeds 100 ul/min, tear overflow may occur even if the tear duct is normal. Primary hypersecretion: such as inflammation of the lacrimal gland, tumor, etc. Pharmacological with neostigmine, organophosphorus pesticides, etc. Central or psychogenic tearing: emotional excitement, sadness, maniacal laughter, pain, etc. Interestingly, central or psychogenic lacrimation is not established until after the first month of life, so the newborn’s cry is a true “dry cry”, with no tears in sight. Autonomic secretion can be seen in actors and hysterical patients. Neurological tears can be induced by stimulation of the trigeminal and facial nerves. The abnormal tearing of some patients while chewing food, the so-called “crocodile tears” phenomenon, is not a cold, but a pathology caused by, for example, dysplasia, birth injury, facial nerve paralysis, etc. Too many tears lead to tear overflow, but what about too few? Dry eyes occur when there are too few tears. Primary: lacrimal gland atrophy, inflammation, old age, conjunctival cupped cell damage. Toxic: atropine poisoning. Nutritional deficiencies: vitamin A deficiency, etc. The most important thing to pay attention to is dry keratitis: a disease in which the corneal epithelium cannot maintain normal function caused by a lack of quality or quantity of the tear film. Lack of tear water secretion from the main lacrimal gland, lack of mucin secretion from the cup cells, lipid abnormalities, abnormal eyelid position, and epithelial lesions can all cause abnormalities. Symptoms include eye irritation, redness or indescribable discomfort in the eye, and dryness at night or upon awakening in the early morning. Complications of dry keratitis, in addition to aseptic corneal stromal ulcers, blepharitis, keratitis, banded corneal degeneration, and corneal epithelialization, are more disturbing to the patient because of the mental anguish, disappointment, and depression. The eyes of dry eye patients, especially those of middle-aged and elderly patients, are exactly like the eyes of Mrs. Xianglin who wants to cry, reflecting the helplessness of corneal dryness and as if containing deep traumatic pain of life. The diagnosis of dry eye can be made by Bengal rose stain, BUT test, Schirmer test, etc. Dry eye treatment firstly targets the cause and symptomatic treatment includes tear supplementation: polyvinyl alcohol, hydroxypropyl cellulose slow release artificial tears; reduction of tear loss: evaporation reduction, tear point closure (tear point plugs, collagen plugs); surgery; application of mucin scavengers and drugs to stimulate tear secretion. Overall, there is no best method yet. There is a rain of tears, and after the rain of tears there are still bright, clear eyes. Tearless eyes desperately look forward to the compassionate hands of scientists. People, who thought that tears are so simple and transparent, find that they contain many unknown mysteries.