TEARS

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TEARS: TEARS Protective layer Watery liquid-Bathes/Nourishes Three layers: Lipid, Aqueous and Mucin Tear – secreted by glands around the eyelid

TEAR PRODUCTION: TEAR PRODUCTION Lipid layer – Meibomian glands & Glands of Zeis Aqueous layer – Lacrimal glands, Glands of Krause & Wolfring Mucin Layer Goblet cells

PHYSICAL CHARACTERISTICS OF TEAR FILM: PHYSICAL CHARACTERISTICS OF TEAR FILM Surface tension :40-50 dynes/cm2 pH :6.9 -7.4 Osmolarity :290-310 mOsm/l Viscosity :1.9-2 centipoises

FUNCTIONS OF TEAR FILM: FUNCTIONS OF TEAR FILM Lubricates and moistens eye surface Provides nutrients & oxygen to cornea Washes away foreign bodies Protects against bacteria and viruses (with help of enzyme Lysozyme)

COMPOSITION OF TEAR FILM: COMPOSITION OF TEAR FILM Lipid layer Proteins (albumin, globulin) Lysozyme (antibacterial) Aqueous layer Nutrients (minerals,Vitamins, electrolytes) Mucin layer Glycoproteins make the corneal surface more hydrophilic

FUNCTIONS OF THE TEAR FILM LAYERS: FUNCTIONS OF THE TEAR FILM LAYERS Lipid layer Prevents evaporation of aqueous layer. Aqueous layer Nourishes and moisturizes the cornea and sclera. Protects against micro-organisms Mucin layer Helps in the even spreading of the tear film over the ocular surface

TEAR SECRETION : TEAR SECRETION Two types of secretors :- basic and reflex Basic secretors Supply tears at constant rate – gland of Krause and wolfring Reflex secretors Supply tears when there is a stimulus like foreign body, emotions, bright light.

BLINKING: BLINKING Provides regular rewetting Ensures normal tear film function Tear Break Up Time (TBUT) – 10 seconds Compromised blinking – leads to SSS (Screen Stare Syndrome)

TEAR DRAINAGE: TEAR DRAINAGE PUNCTA CANALICULI LACRIMAL SAC NASO LACRIMAL DUCT EVAPORATION