Lacrimal Anatomy

 

• Lacrimal Gland
  • separated from orbit by fibroadipose tissue
  • divided by LPS aponeurosis, smaller palpebral portion visible, larger orbital half hidden
  • blood vessels, lymph, nerve, and excretory ducts pass from orbital part through palpebral section
    • don’t biopsy or remove palpebral lobe which might significantly reduce tearing
  • ducts empty 5mm above superior tarsal border
  • reflex tear arc: afferent from V stimulates tear production from lacrimal gland; efferent complicated (with parasympathetics from VII, sympathetics not understood)
  • exocrine gland, acinar and myoepithelial cells, lacrimal artery
• Accessory Glands of Krause and Wolfring
  • no neural control, basal tear production (BST)
  • located in sup fornix & above sup border of tarsus
• Canalicular System
  • puncta sit in tear lake, approx 6mm from canthus, then 2 mm ampulla, then canaliculi extend medially 8-10 mm to common canaliculus (in 90% of population), then to lat wall of tear sac
  • dilation prior to sac: sinus of Maier, enters sac superior and posterior
  • valve of Rosenmuller prevents reflux from sac into common canaliculus during tear pump
  • sac lies btw ant and post crura of med canthal tendon in lacrimal sac fossa
  • puncta/lids move medially with lid closure
  • deep heads of preseptal orbicularis (Horner’s muscle) inserts on post lacrimal crest, lateral half of superior lacrimal sac, encircles canaliculi to help pump
• Bony System
  • interosseos direction of Nasolacrimal Duct = inferior and slightly. lateral, posterior
  • Nasolacrimal Duct is approx 12 mm long, intranasal ostium high up in inf turbinate, covered by valve of Hasner, approx 2.5 cm post to naris on lat wall
  • lacrimal bone very thin, therefore aim posteriorly in DCR
  • ethmoid air cells are at superior and deeper parts of fossa, but may extend under entire fossa
  • mucosa of ethmoid cells gray, thin, and friable
• Lacrimal Pump Model
  • orbicularis actively pumps tears from lake
  • Rosengren-Doane model: orb m contraction > pressure in lacrimal sac > tears forced into nose > lids open, move laterally > - pressure in sac helped by closed valve of Hasner > lids open fully and puncta pop open, with - pressure drawing tears into ampulla and canaliculi
  • Jones model: closure--lateral move = negative pressure
  • Becker model: closure--upper half lateral move = lower pressure, lower half medial move with higher pressure
  • fistulas develop inferior to medial canthal tendon b/c tendon itself is tough