The natural anatomy of the eye allows for our tears to drain into the nose through two small tubes (canalicula) which are connected to the lacrimal sac. Dacryocystitis refers to an infection of this lacrimal sac.
The cause of dacryocystitis is usually a blockage of the nasolacrimal duct, which leads from the lacrimal sac into the nose. The area around the lacrimal sac usually becomes painful, red, and swollen. The eye may become red and watery and may ooze pus. Slight pressure applied to the lacrimal sac may push pus through the lacrimal punctum, the opening at the inner corner of the eye, near the nose. On rare occasions, an abscess may form, which can rupture through the skin, creating a passage for drainage. Dacryocystitis is usually treated with an antibiotics taken orally or intravenously, but applying Eye-presses to the area several times a day also helps expedite recovery, reduce the symptoms from the swelling and the inflammation, help fight the infection by recruiting more white blood cells to the area, and may also help drain the backed up duct. The following reputable links all present detailed information and literature about Dacryocystitis and guidance regarding how to best treat it with warm compresses:
The Merck Manual
The British Journal of Ophthalmology
American Academy of Ophthalmology