Lacrimation

1. Physiology
   1. Layers of tears
      1. Inner: Mucin produced by goblet cells of Conjunctiva
      2. Mid: Aqueous layer by lacrimal glands (90% of tears)
         1. Water (largest component)
         2. Glucose
         3. Lysozyme
         4. Lactoferrin
         5. Secretory Immunoglobulin (IgA)
      3. Outer: Lipids produced by meibomian glands
         1. Prevents evaporation
   2. Function of tears
      1. Maintains smooth eye surface for visual clarity
      2. Lubricates eye surface to facilitate blinking
      3. Barrier to infection
   3. Function of Blinking
      1. Normally, blinking occurs every 5 seconds
      2. Spreads tear film and directs toward lacrimal duct
2. Causes: Increased Tear Secretion
   1. Emotion
   2. Foreign body irritation
   3. Corneal Ulcer
   4. Conjunctivitis
   5. Coryza
   6. Measles
   7. Hay fever
   8. Cluster Headache (unilateral tearing)
   9. Toxin
      1. Chronic iodine toxicity (Iodism)
      2. Chronic bromide toxicity (Bromism)
      3. Arsenic
3. Causes: Absent or decreased Tear Secretion
   1. See Dry Eyes
   2. See Schirmer's Test
4. Causes: Obstruction of the Lacrimal Ducts
   1. Dacryocystitis
   2. Lacrimal calculus
   3. Congenital obstruction
   4. Cicatrix
   5. Eyelid edema
5. References
   1. Rheinstrom in Yanoff (1999) Ophthalmology, Mosby, 14.1