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