Anatomy of the Nasolacrimal System

  • The purpose of the nasolacrimal system is to:
    • Drain tears from the ocular surface to the lacrimal sac and, ultimately, the nasal cavity
    • Blockage of the nasolacrimal system:
      • Can cause tears to flow over the eyelid and down the cheek:
        • This condition is epiphora
  • Structure and Function:
    • Both the upper eyelid and the lower eyelid have a small opening on the surface of the eyelid margin near the medial canthus:
      • These are called puncta:
        • Each puncta leads to a drainage canal that eventually flows into the lacrimal sac and then the nasal cavity
    • The drainage canal connecting the ocular surface to the nasal cavity consists of multiple parts:
      • Within the lower eyelid:
        • The punctum leads to a 2 mm long ampulla:
          • Which runs perpendicular to the eyelid margin
        • The ampulla turns 90 degrees medially:
          • Becoming the inferior canaliculus and travels 8 to 10 mm before reaching the common canaliculus
        • The upper canaliculus travels 2 mm superiorly in the eyelid before turning 90 degrees medially and moving 8 to 10 mm before connecting to the common canaliculus
      • The common canaliculus:
        • Drains into the lacrimal sac
      • Within the junction between the common canaliculus and the lacrimal sac:
        • Is the valve of Rosenmuller:
          • This apparatus is a one-way valve that prevents reflux from the lacrimal sac to the puncta
    • The lacrimal sac drains:
      • Inferiorly to the nasolacrimal duct:
        • Which is bordered:
          • Medially by:
            • Palatine bone and the inferior turbinate in the nose
          • Laterally by:
            • Maxillary bone
      • The nasolacrimal duct:
        • Opens at the inferior meatus:
          • Located underneath the inferior nasal turbinate
      • The lacrimal sac is:
        • Approximately 10 to 15 mm in axial length and 13 to 20 mm in corneal length
      • The nasolacrimal duct is:
        • 12 to 18 mm long
      • The inferior nasal meatus is partially covered by a mucosal fold:
        • Known as the valve of Hasner
  • Embryology:
    • The nasolacrimal duct:
      • Starts forming around five weeks of gestation
      • It starts out as a linear thickening of ectoderm:
        • Located in a groove between the nasal and maxillary prominences
      • This thickening:
        • Eventually separates into a solid cord and sinks into the surrounding mesenchyme
        • Over time the cord canalizes:
          • Forming the lacrimal sac and the beginning of the nasolacrimal duct
      • The nasolacrimal duct extends:
        • Intranasally until it exits under the inferior turbinate
      • The lacrimal sac extends caudally:
        • To complete the canalicular system
      • The inside of the canal breaks down and forms a lumen:
        • So that the nasolacrimal system is patent:
          • This process is generally complete by the time of birth
  • Blood Supply and Lymphatics:
    • Blood supply to the nasolacrimal area of the face:
      • Is generally from the angular artery:
        • The angular artery is considered a branch of the facial artery:
          • However, some studies have shown that it can originate from the ophthalmic artery in some individuals
        • It terminates in anastomosis with the dorsal nasal branch of the ophthalmic artery
        • The angular artery and vein:
          • Appear alongside the nose near the medial orbit
        • A correlating angular vein drains this region
    • The medial and lateral portions of the eyelids have different lymphatic drainage systems:
      • The medial one-third of the upper eyelid and the medial two-thirds of the lower eyelid:
        • Drain to the submandibular lymph nodes
      • The lateral two-thirds of the upper eyelid and the lateral one-third of the lower eyelid:
        • Drain to the pre-auricular lymph nodes
  • Nerves:
    • Cranial nerve VII:
      • Supplies the motor innervation to the muscles of the face
    • The movement of these muscles:
      • Aid in proper drainage of the tears through the nasolacrimal system:
        • By what is known as the lacrimal pump mechanism
    • Cranial nerve III and cranial nerve VII:
      • Innervate the muscles that control the blinking of the eyelids:
        • This action is the primary driver of the lacrimal pump mechanism
    • Irritation of the ocular surface:
      • Stimulates the ophthalmic branch of cranial nerve five:
        • Which begins the reflex tear arc pathway:
          • The efferent pathway involves cranial nerve VII and parasympathetic fibers
        • The role of the sympathetic nervous system in tear production:
          • Is not well understood
  • Muscles:
    • The action of the orbicularis muscle and surrounding tissues:
      • Helps propel the flow of tears from the canaliculi to the nasolacrimal duct:
        • Via the lacrimal pump mechanism
  • References:
    • Computed tomography dimensions of the lacrimal gland in normal Caucasian orbits., Tamboli DA,Harris MA,Hogg JP,Realini T,Sivak-Callcott JA,, Ophthalmic plastic and reconstructive surgery, 2011 Nov-Dec.
    • An Unusual Case of Nasolacrimal Obstruction Caused by Foodstuffs., Matsumoto H,Matsumoto A,, Case reports in ophthalmology, 2015 Sep-Dec.
    • Lacrimal Gland Volume Changes in Unilateral Primary Acquired Nasolacrimal Obstruction., Yazici A,Bulbul E,Yazici H,Sari E,Tiskaoglu N,Yanik B,Ermis S,, Investigative ophthalmology & visual science, 2015 Jul.
    • Incidence of neoplasia in patients with unilateral epiphora., Bewes T,Sacks R,Sacks PL,Chin D,Mrad N,Wilcsek G,Tumuluri K,Harvey R,, The Journal of laryngology and otology, 2015 Jul.
    • Ducasse A,Arndt C,Brugniart C,Larre I, [Lacrimal traumatology]. Journal francais d’ophtalmologie. 2016 Feb.
    • Modified External Dacryocystorhinostomy in Primary Acquired Nasolacrimal Duct Obstruction., Sharma HR,Sharma AK,Sharma R,, Journal of clinical and diagnostic research : JCDR, 2015 Oct.

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