The lacrimal sac or lachrymal sac is the upper dilated end of the nasolacrimal duct, and is lodged in a deep groove formed by the lacrimal bone and frontal process of the maxilla. It connects the lacrimal canaliculi, which drain tears from the eye's surface, and the nasolacrimal duct, which conveys this fluid into the nasal cavity. Lacrimal sac occlusion leads to dacryocystitis. 
It is oval in form and measures from 12 to 15 mm. in length; its upper end is closed and rounded; its lower is continued into the nasolacrimal duct.
Its superficial surface is covered by a fibrous expansion derived from the medial palpebral ligament, and its deep surface is crossed by the lacrimal part of the orbicularis oculi, which is attached to the crest on the lacrimal bone.
Like the nasolacrimal duct, the sac is lined by stratified columnar epithelium with mucus-secreting goblet cells, with surrounding connective tissue. The Lacrimal Sac also drains the eye of debris and microbes.
It serves as a reservoir for overflow of tears, in which the lacrimal sac pumps inward and outward driven by the orbicularis muscle during blinking.
The lacrimal apparatus. Right side. (Lacrimal sac visible at upper right.)
- Dr. Johannes Sobotta (1909). Sobotta's Atlas and Textbook of Human Anatomy. Philadelphia.
- Sacks, Raymond; Naidoo, Yuresh (2019-01-01). Endoscopic Dacryocystorhinostomy. ScienceDirect. pp. 143–148.e1. doi:10.1016/B978-0-323-47664-5.00017-1. ISBN 9780323476645. Retrieved 2020-05-08.
Anatomy: The lacrimal sac extends approximately 10 mm above the axilla of the middle turbinate.
- Remington, Lee Ann (2012). "Ocular Adnexa and Lacrimal System". Clinical Anatomy and Physiology of the Visual System. Elsevier. pp. 159–181. doi:10.1016/b978-1-4377-1926-0.10009-8. ISBN 978-1-4377-1926-0.
The lacrimal sac lies within a fossa in the anterior portion of the medial orbital wall. This fossa is formed by the frontal process of the maxillary bone and the lacrimal bone. The sac is surrounded by fascia, continuous with the periorbita, which runs from the anterior to the posterior lacrimal crests.
- Beare, Nicholas A.V.; Bastawrous, Andrew (2014). "Ophthalmology in the Tropics and Sub-tropics". Manson's Tropical Infectious Diseases. Elsevier. pp. 952–994.e1. doi:10.1016/b978-0-7020-5101-2.00068-6. ISBN 978-0-7020-5101-2.
Tears drain through the canaliculi, lacrimal sac and naso-lacrimal duct into the nose. Blockage of the naso-lacrimal duct prevents drainage of the lacrimal sac, which may lead to infection, causing a painful swelling at the side of the nose below the medial canthus. This may present as a chronically watery, discharging eye, or as an acutely inflamed abscess. This should be treated with oral broad-spectrum antibiotics. The problem may recur unless drainage into the nose is re-established.