Overview

The lacrimal system has two functional components: the secretory system (which produces tears) and the excretory system (which drains them). The two components must be in balance — inadequate drainage causes overflow, while inadequate production causes dry eye.

Tears flow across the ocular surface from lateral to medial with each blink, collecting in the medial lake (lacus lacrimalis) near the inner corner of the eye. They then enter the drainage system through small openings at the inner edge of each lid margin.

Tear Film & Production

The tear film is a three-layer structure essential for optical clarity and corneal nutrition:

The Complete Drainage Pathway

Tears drain through a series of structures from the ocular surface into the nasal cavity:

1. 1
   Puncta

   Two small oval openings — one on the upper lid and one on the lower lid — located at the medial end of each lid margin on a small elevation called the lacrimal papilla. Each is approximately 0.3 mm in diameter. Punctal stenosis (narrowing) is a common cause of tearing.

2. 2
   Canaliculi

   Narrow tubular channels leading from each punctum to the lacrimal sac. Each canaliculus has a short vertical portion (2 mm) then turns medially for a horizontal portion (8–10 mm). The upper and lower canaliculi typically join into a common canaliculus (90% of people) before entering the lacrimal sac.

3. 3
   Valve of Rosenmuller

   A mucosal fold at the junction of the common canaliculus and lacrimal sac that acts as a one-way valve, preventing reflux of tears back from the sac into the canaliculi.

4. 4
   Lacrimal Sac

   A small reservoir (12–15 mm tall, 4–8 mm wide) lying in the lacrimal fossa — a groove in the medial orbital wall formed by the lacrimal bone and frontal process of the maxilla. The sac sits anterior to the orbital septum, between the anterior and posterior limbs of the medial canthal tendon.

5. 5
   Nasolacrimal Duct

   A bony canal approximately 12–18 mm long running inferolaterally within the maxillary bone to open into the inferior nasal meatus. Its lower end is guarded by the valve of Hasner — a mucosal fold that prevents nasal air from blowing back up the duct. This valve fails to open in congenital NLDO.

6. 6
   Valve of Hasner

   The distal valve of the nasolacrimal duct at its opening into the inferior nasal meatus. Failure of this valve to fully canalize before birth is the cause of congenital nasolacrimal duct obstruction (CNLDO) — affecting approximately 6% of newborns.

Puncta & Canaliculi — Detailed Anatomy

Lacrimal Sac

The lacrimal sac lies in the lacrimal fossa at the medial orbital wall. It is the target structure in dacryocystorhinostomy (DCR) surgery, in which a new bony window is created between the sac and the nasal cavity.

Nasolacrimal Duct

The nasolacrimal duct (NLD) runs inferiorly within the bony nasolacrimal canal, angled slightly laterally and posteriorly. It is entirely enclosed in bone for most of its length before opening into the inferior meatus of the nasal cavity.

The Lacrimal Pump

Tear drainage is not passive — it depends on an active pumping mechanism powered by the orbicularis oculi muscle with each blink.

Clinical Relevance