In the ophthalmology clinic of Beijing Children’s Hospital, parents often see newborns who are just 10 days old or even less than 10 days old, and some of them will obviously see a greenish-purple lump bulging in one or both lacrimal sac areas, and it is also hard. What is this disease? Why are they only found in such young babies? The ophthalmologists at Beijing Children’s Hospital tell us that this disease is called “congenital tear sac protrusion”. So, how did this disease come about? Studies have shown that 35-73% of fetuses in the second trimester have atresia of the Hasner valve at the end of the lacrimal duct, and that crying, breathing movements and tears can help the Hasner valve to rupture spontaneously after birth. When the Hasner valve continues to rupture without rupture, it can cause secretions to accumulate in the nasolacrimal duct and the lacrimal sac and increase the pressure, which then leads to functional atresia of the Rosenmuller valve at the junction of the common lacrimal duct and the lacrimal sac, which results in dilation of the lacrimal sac and the membranous nasolacrimal duct, forming congenital lacrimal sac protrusion. The main clinical manifestations of congenital lacrimal sac protrusion include: tearing, bulging of the lacrimal sac area on the affected side, nasal congestion on the affected side and, in the case of bilateral disease, breathing difficulties and breath-holding during suckling, which are the reasons why most parents bring their children to the hospital. It is important to note that up to 60-70% of cases of this disease develop into acute dacryocystitis and orbital cellulitis due to secondary infection, which can endanger the life of the newborn. Therefore, the treatment of this disease should be treated with an aggressive attitude and should not be ignored!