3.1.7 Flashcards
What are the functions of the tear film
Optical- provides smooth (not flat) refractive surface. Inconsistent vision if affected. Smooth optical system as it provides good wetting.
Immune system- bactericidal, chemical and cellular components. Susceptible to infection if affected. Some proteins have anti microbial properties with bathes cells of the cornea and conjunctiva to keep them healthy
Nutritional- source of oxygen from atmosphere and ions to epithelial surface.
Surface maintenance- remove debris from environment and epithelial cells with blinking and constant replenishment.
Protective
Explain the structure of the tear film
Secretory system, distribution system, excretory system.
Lipid, aqueous and mucus phase
Explain the lipid phase
0.2 micro metres
Polar and non polar layer
Major components- cholesterol and phospholipid
Retards evaporation
Maintains optically smooth surface
Meibomium glands
Ciliary glands ( of mol)
Sebaceous glands (of Zeiss)
Explain the aqueous phase
3 micro metres
Proteins, soluble mucins, lipids, electrolytes and other organic components (water, protein and salts)
Lacrimal gland- wolf ring and Krause
Lysozyme (adheres easily to negatively charged substrates), lipocalin, lactoferin
Bacteriostasis, flushing debris, epithelial hydration
Explain the mucus phase
0.5 micro metres
Membrane bound and secreted
Renders epithelial surface
Hydrophilic for aqueous to wet
Goblet cells ( conjunctiva)
MUC1, MUC4, MUC16, produced by superficial corneal and conjunctival epithelial cells
Soluble mucins MUC7 and MUC8 small molecules produced by lacrimal gland
Glycoproteins ( membrane bound or secretory)
Non invasive techniques of assessing the tear film
Stability - NITBUT using keratometer, placido disc
Structure and quality- tearscope (hand held system on the SL, once see areas of break up hit stop button and do it 3 times)
Quantity/ volume- tear meniscus/ tear prism height
Invasive techniques of assessing the tear film
These tests alter the nature and structure of the tear film
Quantity/volume - Schirmer test, phenol red thread
Stability- TBUT with fluorescein
Anterior surface integrity- fluorescein, rose bengal and lissamine green
LIPCOF (lid parallel conjunctival folds) seen temporally and nasally to lower eye . Single to multiple folds. Frictional (CLs) or mechanical. Managed by lubricaton. More folds, more likely to have dry eye.
Lid wiper epitheliopathy- seen by appearance of Marx line- use lissamine green a thin line/ no staining is normal- thicker the staining the greater indication of dryness.
Tear film osomolarity - detection and grading of dry eye disease, normal 302, 315 mod 336 severe
OCT- can see tear meniscus and tear film thickness in cross section
