The lacrimal apparatus can be structurally and functionally divided into the tear-secreting and tear-discharging divisions. The tear-secreting part includes lacrimal glands, paracrine glands, conjunctival cupped cells and other exocrine glands. The lacrimal glands are reflex secretion glands, which secrete a large amount when stimulated by external stimuli (e.g., corneal foreign bodies, chemical stimuli, etc.) or emotional excitement, and play the role of flushing and diluting stimuli. The paracrine lacrimal glands are basic secretory glands that secrete very little tear fluid, which is the basic tear fluid that reduces friction between the eyelids and eyeballs and moistens the cornea and conjunctiva under normal conditions. The conjunctival cupped cells secrete mucin, which helps to keep the ocular surface lubricated. Disruption of the cupped cells can cause corneal dryness, even if the lacrimal glands are producing normally. In addition, lipids secreted by the lid glands and lid margin sebaceous glands are also involved in the composition of the tear film. The lacrimal drainage (lacrimal duct) consists of the upper and lower lacrimal dots, the upper and lower lacrimal ducts, the common lacrimal duct, the lacrimal sac, and the nasolacrimal duct, whose main function is to drain tears into the nasal cavity. Under normal conditions, the tears produced by the lacrimal gland disappear through evaporation, but a portion of the tears are discharged through the lacrimal duct by the “tear pump” of the orbicularis oculi muscle. When the eyelid is opened, the orbicularis oculi muscle relaxes and the lacrimal duct and the lacrimal sac dilate due to their own elasticity, creating a negative pressure in the lumen, and the tears that accumulate in the lacrimal lake are drawn into the lacrimal duct and the lacrimal sac through the open tear dots. The capillary action of the lacrimal duct also helps the tears to enter the lacrimal duct. During eyelid closure, the tear dots are temporarily closed and the orbicularis oculi muscle contracts, squeezing the lacrimal ducts and the lacrimal sac, forcing the tears in the lacrimal sac to drain into the nasal cavity through the nasolacrimal duct. Tear flow is one of the main symptoms of lacrimal disease and has two causes: first, the discharge is obstructed and tears cannot flow into the nasal cavity and overflow outside the eyelid, called tear overflow; second, tear secretion increases and the discharge system is too late to drain away and flow out of the eyelid, called tear flow. It is important to distinguish clinically between tear overflow due to tear duct obstruction and tear flow due to ocular surface disease stimulation. Nasolacrimal duct obstruction can often cause secondary infection of the lacrimal sac, resulting in chronic dacryocystitis. As a common lacrimal tract infection, chronic dacryocystitis is a potential threat to the eye. In addition, inadequate secretion of the lacrimal base is an important factor in causing ocular surface disease. Diseases of the lacrimal gland are relatively rare and are mainly inflammatory and neoplastic.