Tears Flashcards
What are the 7 functions of the tear film?
Moisture/Hydration to ocular surface
Lubrication between the globe and eyelids
Traps and eliminate debris (e.g. sloughed epithelial cells, fb’s)
Oxygen for cornea (primary source)
Primary refractive surface
Antibacterial
Growth factors and peptides (wound healing)
What are the components of the tear film?
Proteins (peptides, removal of epithelial cellular debris, antimicrobial)
Growth factors (promote healing)
Immune mediators
Cytokines
What is the total volume of tears on the ocular surface?
How much tears are produced per min?
What is the max volume the eye/lids can hold?
Total volume = 7-10 mL
Normal tear production ~1mL/min
The eye/lids can hold ~20-30 mL
What is the tonicity of the tear film?
Isotonic
Describe the pH and buffering ability of tears?
Average pH is 7.45
Tears have good buffering ability (eye can tolerate pH 3.5-10.5)
During sleep the tears become more acidic
Most eye drops are weak bases to allow better absorption
Osmolarity of the tear film.
Electrolytes are responsible for the osmolarity
Highly variable measurements
Measured from lower meniscus
What are the different compartments of the tear film?
Behaves as a single dynamic functional unit
Fornical (occupies the fornix and retrotarsal space)
Tear Menisci
Preocular Tear Film (overlies the exposed
conjunctiva and cornea)
What are the components of the tear film?
Primarily composed of lipids, aqueous, and mucins Organized, generally into 2 component layers:
• Lipid component
• Mucoaqueous component
Spreading of tears
Respreadability, Fluidity, Incompressible structure
Describe the lipid component of the tear film.
High evaporation resistance
Respradabiliy
Fluidity
Gel-like incompressible structure
Lowers surface tension at air interface
Derived from Meibomian gland secretions (2nd Zeiss)
Describe the anatomy of the meibomian glands.
Parallel rows through the length of the tarsal plates in the upper and lower lids
Single gland with clusters of secretory acini arranged around a long duct connected by short ductules (Brussel sprouts)
Describe secretion by meibomian glands.
Continuous production of meibum
Hormonal and neural regulation
Mechanical forces of muscle contraction during the eye blink
Glands open anterior to mucocutaneous junction, oily secretion delivered onto precorneal tear film
Meibomian gland histology
The internal ductal system is lined by stratified squamous
epithelium
Incipient keratinization
What kind of secretion do acinus have? What type of cells are they filled with?
Holocene secretion
Filled with secretory cells (meibocytes)
Describe meibocytes
Proliferating progenitor cell population
4 days to generate new cells
Progressive accumulation of lipids in the cytoplasm
Oily secretory product termed meibum
