Tears enter the lacrimal drainage system through puncta located medially on the margin of the upper and lower eyelids (Fig 14-2). Each punctum appears at the apex of a fleshy papilla that protrudes slightly above the eyelid margin and is slightly inverted and apposed to the globe to rest within the tear lake. The inferior punctum is slightly more lateral than the superior. The puncta are approximately 0.3 mm in diameter and lead to a vertical segment of the lacrimal canaliculi known as the ampulla. The canaliculi then turn 90°, continuing 8–10 mm medially to join at the common canaliculus and connect with the lacrimal sac through the valve of Rosenmüller. Less commonly, the canaliculi connect directly to the lacrimal sac without a common portion. The canaliculi are lined with nonkeratinized, non–mucin-producing stratified squamous epithelium. This epithelium transitions to a stratified columnar epithelium in the distal portion of the canaliculi, which continues through the lacrimal sac and nasolacrimal duct (NLD). For reasons that are not completely understood, the Na+/I (sodium/iodide) symporter (NIS) is present in this epithelium, which can lead to stenosis during treatment with high-dose radioactive iodine for thyroid cancer.
Figure 14-2 Normal anatomy of the lacrimal drainage system. The measurements given are for adults.
(Illustration by Mark Miller.)
The valve of Rosenmüller (see Fig 14-2) is a fold of mucosal tissue that has traditionally been described as the structure that prevents reflux of tears from the sac into the canaliculi. However, studies suggest that the common canaliculus consistently bends from posterior to anterior behind the medial canthal tendon before entering the lacrimal sac at an acute angle. This bend, in conjunction with the fold of mucosa, may play a role in blocking reflux.
The lacrimal sac lies within a bony fossa bordered by the anterior and posterior lacrimal crests (see BCSC Section 2, Fundamentals and Principles of Ophthalmology, Fig 1-1, for an illustration of this fossa). Wrapping around the anterior and posterior aspects of the lacrimal sac, the medial canthal tendon is a complex structure composed of anterior and posterior crura. The superficial head attaches to the anterior lacrimal crest; the deep head (with the Horner muscle), to the posterior lacrimal crest. The medial wall of the fossa is composed of the lacrimal bone posteriorly and the frontal process of the maxillary bone anteriorly. Medial to the fossa is the middle meatus of the nose, sometimes with intervening ethmoid air cells. From an intranasal view, the location of the lacrimal sac corresponds to the lateral nasal wall just anterior to the middle turbinate (Fig 14-3). The fundus of the sac, which is more fibrous than the rest of the sac, extends several millimeters above the medial canthal tendon. Inferiorly, the lacrimal sac transitions into the NLD. When performing an external dacryocystorhinostomy, the surgeon may encounter the angular artery and vein medial to the medial canthal angle, which may cause bleeding. Additionally, distal fibers of the zygomatic and buccal branches of the facial nerve may be affected, resulting in temporary lagophthalmos.
In adults, the NLD measures 12–18 mm in length. The intraosseous portion of the duct is typically 12 mm long, and the meatal duct extends 5–6 mm inferior to the bony ostium. The NLD travels through bone within the nasolacrimal canal, which initially curves in an inferior and slightly lateral and posterior direction from the lacrimal sac. The NLD opens into the nose through an ostium under the inferior turbinate (the inferior meatus), which is usually partially covered by a mucosal fold (the valve of Hasner; see Fig 14-2). The mucosal ostium in adults is typically located 30–35 mm from the external naris.
Figure 14-3 Endoscopic intranasal anatomy (left side). Note the septum (A), middle turbinate (B), and area of mucosa and bone to be removed to expose the lacrimal sac (C). The superior portion of the inferior turbinate is visible at the bottom (D).
(Courtesy of Eric A. Steele, MD.)
Morgenstern KE, Vadysirisack DD, Zhang Z, et al. Expression of sodium iodide symporter in the lacrimal drainage system: implication for the mechanism underlying nasolacrimal duct obstruction in I131-treated patients. Ophthalmic Plast Reconstr Surg. 2005;21(5):337–344.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.