There are 4 main causes of eye tearing: 1. Excessive tear secretion caused by tissue lesions or foreign bodies, UV rays and chemicals stimulated by the conjunctiva, cornea, iris, ciliary body, etc. For example: severe viral and bacterial conjunctivitis; keratitis or corneal ulcer; corneal epithelial abrasion, corneal epithelial detachment, corneal foreign body, conjunctival sac foreign body, etc.; 2. Due to obstruction of the lacrimal system, the normally secreted tears cannot drain smoothly into the nasal cavity through the nasolacrimal duct, but instead reflux and overflow. For example: tear point obstruction, tear duct obstruction, nasolacrimal duct obstruction, chronic dacryocystitis, etc. 3. Due to eyelid deformity and lower lid ectropion, the tear dots located on the lower lid cannot be close to the eyeball, and tears cannot enter the tear dots, and tears cannot enter the nasal cavity by the tear ducts, thus overflowing. Because the normal tear dots are immersed in the tear lake and touch the bulbar conjunctiva, even if the patient is made to look upward, the lower tear dots will not be visible without wrenching the lower lid open. This close contact is a prerequisite for maintaining normal tear attraction. 4. Difficulties in eyelid closure, such as facial nerve palsy leading to relaxation of the orbicularis oculi muscle, epileptic shrinkage or weak expansion of the lacrimal sac, resulting in insufficient suction of the lacrimal sac, can also lead to tears not entering the tear duct properly and thus overflowing. Therefore, a variety of eye diseases can present with symptoms of watery eyes.