Lacrimal sac

The lacrimal sac (Latin: saccus lacrimalis) is the upper dilated segment of the nasolacrimal duct that is a part of the tear drainage system of the lacrimal apparatus.

Structure of the lacrimal sac

The lacrimal sac is situated in the inferomedial aspect of the orbit, embedded in a deep lacrimal fossa located at the beginning of the nasolacrimal canal formed by the lacrimal bone and the frontal process of the maxilla. 

The lacrimal sac is enclosed by the lacrimal fascia and the lacrimal part of the orbicularis oculi muscle.

The size of the lacrimal sac is about 1.5 cm in length and 0.5 cm in width, and it is oval in form. It is approximately 12 mm long. Its dome-shaped upper margin is called the fornix of the lacrimal sac. The lower part of the lacrimal sac continues directly into the nasolacrimal duct. 

The lacrimal sac connects the superior and inferior lacrimal canaliculi, which drain tears from the eye surface, with the nasolacrimal duct, which opens into the nasal cavity. The lacrimal sac drains into the nasolacrimal duct via the valve of Krause, which is a fold of mucous membrane at the junction between the lacrimal sac and the nasolacrimal duct.

Function of the lacrimal sac

The main function of the lacrimal sac is to serve as a reservoir for the overflow of tears. The excess tears are pumped inward and outward by the lacrimal sac during blinking with the help of contractions of the lacrimal part of the orbicularis oculi muscle.

Vasculature and innervation of the lacrimal sac

The lacrimal sac receives blood from the branches of:

  • The medial palpebral artery from the ophthalmic artery
  • The facial artery
  • The infraorbital artery from the maxillary artery
  • The sphenopalatine arteries from the maxillary artery

The lacrimal sac is innervated by the infratrochlear nerve from the ophthalmic division of the trigeminal nerve (CN V), and by the anterior superior alveolar nerve from the maxillary division of the trigeminal nerve.