A drain is a widely used surgical instrument that drains fluid from a closed system to a specific location. They are commonly used in the treatment of glaucoma and in chest and abdominal surgeries to drain fluids out of the body. 1. Glaucoma treatment: Glaucoma often leads to high intraocular pressure (IOP), which can be effectively controlled with fewer side effects by inserting specific drains. 2. Abdominal drain: Thoracic and abdominal trauma, cancer, inflammation and other diseases may cause fluid accumulation in the thoracic and abdominal cavities, and then a drain is needed to drain the fluid out of the body. Sometimes abdominal surgery involving the cavity organs, in order to have a better prognosis after the operation, it is necessary to put a drain inside the cavity organs to drain the secretion fluid to the outside, and then take off the drain after the wound heals after the operation. Patients can observe the color of the fluid in the drain to determine the development of the disease, and if there is any abnormality, they should contact the doctor in time to avoid adverse consequences.