Functional and Surgical Anatomy of the Lacrimal System
Sanja G. Cypen, MD
AFFERENT LACRIMAL SYSTEM
The afferent lacrimal system is responsible for tear production. Tears are produced constantly at a very small rate. Basal tears are a complex composition of growth factors and antibodies. They serve to lubricate and nourish the ocular surface and provide both specific and nonspecific immunity. Reflex tears are produced in very large quantities — up to 100× the basal tear production. They are produced in response to ocular irritation or emotional stimuli. Reflex tears have a different chemical composition from basal tears and serve to remove irritants from the ocular surface.
Lacrimal gland
Located in the lacrimal gland fossa in the anterior superotemporal orbit just posterior to the orbital rim
Bilobed with orbital and palpebral lobes separated by the lateral horn of the levator aponeurosis
Accessory lacrimal glands
Glands of Krause are located in the forniceal conjunctiva:
Approximately 40 glands in the upper fornix
Approximately six to eight glands in the inferior fornix
Glands of Wolfring are located in the conjunctival surface at the superior tarsal border. They are slightly larger than the glands of Krause, and there are usually two to five glands (Figure 3.1).
EFFERENT LACRIMAL SYSTEM
The efferent lacrimal system is responsible for tear drainage. Tears are spread across the ocular surface with each blink. Some tears are removed through evaporation, whereas the remainder drain into the efferent lacrimal system located medially. The total length of the efferent system is approximately 35 mm (Figure 3.2). Some tears transit the system and drain into the posterior nasopharynx, whereas some tears are absorbed across the lining of the nasolacrimal duct (NLD).
 FIGURE 3.1. Schematic of the afferent lacrimal system, which includes the orbital and palpebral lobes of the lacrimal gland and the accessory lacrimal glands of Krause in the conjunctival fornices and Wolfring at the superior tarsal border. |
 FIGURE 3.2. Schematic of the efferent lacrimal system, which functions to drain tears from the ocular surface into the nasal cavity. |
Punctum — seated within the ampulla of the medial eyelid. The puncta average 0.3 mm in diameter. The lower eyelid punctum is located just lateral to the upper eyelid punctum.
Canaliculus — consists of a 2 mm vertical component proximally. The canaliculus then turns 90° and runs medially and parallel to the lid margin for a distance of 8 to 10 mm (longer in the lower lid because of the more lateral position of the punctum). The canaliculi are lined by stratified squamous epithelium and serve a transit role in the passage of tears. It is theorized that contraction of the orbicularis oculi muscle compresses the canaliculi, creating a negative pressure that draws tears into the efferent lacrimal system.
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