Babies don’t cry, but their eyes are always teary, even teary, as if they have an endless supply of tears. Why is this? The most common cause of this condition is congenital nasolacrimal duct obstruction in babies. So, what is the relationship between nasolacrimal duct obstruction and tearing? To better understand this condition, let’s first look at how tears are produced and drained. Tears are produced by an organ called the lacrimal gland, which is located in the upper part of the eye sockets and whose main function is to lubricate the cornea and the eye. The secretion of the lacrimal gland takes place every minute of every day, and the discharge of tears into the nasal cavity through the lacrimal ducts is also an ongoing process. The opening of the lacrimal duct is located in the inner canthus of the eye, from where tears enter the lacrimal duct and the common lacrimal duct, and then the common lacrimal duct enters the lacrimal sac, which is a temporary storage pool for tears, and when the tears are stored to a certain extent, they are then discharged into the nasal cavity through the nasolacrimal duct. Congenital nasolacrimal duct obstruction is due to congenital abnormal development of the nasolacrimal duct. Usually the nasolacrimal duct is closed at the opening of the nasal cavity by a layer of undegraded membrane-like structures, so that the normal channels of tear drainage are blocked, so that the baby is always teary-eyed all day long. Over time, the skin at the inner canthus often has tear marks. The water does not rot, and the door is not worm-eaten. Failure to excrete tears properly can lead to tear sac infections. Most children with congenital nasolacrimal duct obstruction suffer from dacryocystitis. The main manifestation is the flow of purulent fluid in addition to tears. When the lacrimal sac is squeezed, a large amount of purulent tears return to the inner canthus and the entire conjunctival sac. At this point, the eye is in a conjunctival sac environment that contains a lot of bacteria, and the entire eye is surrounded by bacteria, which can lead to keratitis in the event of minor ocular trauma or corneal scratches, and severe keratitis often affects vision. It is reassuring to know that congenital nasolacrimal duct obstruction may still open on its own after 6 months of life, but it requires frequent doses of antibiotic eye drops, as well as assisted tear sac massage to prevent dacryocystitis. If after 6 months of age the duct does not open on its own, lacrimal duct probing is possible. However, because the opening of the nasolacrimal duct created by this procedure is small, it is often blocked again. In some cases of refractory congenital nasolacrimal duct obstruction, it is still difficult to be cured after several lacrimal duct explorations. For these cases, the traditional treatment is to remove part of the nasal bone through a facial skin incision and perform a nasolacrimal duct anastomosis. However, because the nasal bones of children are not fully developed, this surgical method is more traumatic and will leave scars on the face, affecting the appearance, and therefore is not suitable. To date, the treatment of refractory congenital nasolacrimal duct obstruction remains a clinical challenge for ophthalmologists. Nowadays, pediatric ophthalmology uses a new surgical method, namely: using a nasal endoscope to make a normal-sized nasolacrimal duct opening from the bottom up in the normal opening of the nasolacrimal duct, and the postoperative tear drainage is unobstructed. Since this procedure does not make a surgical incision from the face, no scar is left on the external view and the trauma is minimal, so better clinical results are received. It is important to note that if the child is only tearing in the wind and there is no abnormality indoors, the child is usually suffering from conjunctivitis rather than nasolacrimal duct obstruction. Congenital nasolacrimal duct obstruction is a common and frequent disease in pediatric ophthalmology clinics. With timely treatment, there is usually a better outcome. If treatment is delayed, there are serious dangers. Therefore, young parents are advised: if you find any of these conditions in your child, you should go to the hospital promptly to get early diagnosis and timely treatment.