CONTACT LENSES

1. TEAR FILM
CONTENTS
1 ANATOMY
2. PHYSIOLOGY

2. ANATOMY OF TEARFILM
Wolf firstly describedthe structureand called it as “PRE CORNEAL TEARFILM”
From posterior to anterior, it consists of three layers
■ Mucin Layer
■ Aqueous Layer
■ Lipid Layer

3. Mucin Layer
■ It is the innermostlayer
■ Thickess-0.2mm
■ Secreted by conjunctival goblet cells and gland of manz

4. Aqueous Layer
■ Middle layer
■ Thickness-7mm
■ Secreted by main and accessorylacrimal gland
■ It contains proteins,immunoglobulin,urea,glucoseetc....

5. Lipid Layer
■ Outermostlayer
■ Thickness-0.1mm
■ Secreted by Zeis and Moll gland
■ This layer prevents overflow of tears and evaporation

7. FUNCTIONS OF TEAR FILM
■ Keeps the cornea and conjunctivamoist
■ Maintain corneal surfaceoptically uniform
■ Provide oxygen to the corneal epithelium
■ Washes away the debris and irritants
■ Prevent infection due to the presence of lysozyme
■ Facilitate the movementof lid over the globe

8. PHYSIOLOGY OF TEAR FILM
Tear film dynamics mainly consists of two stages;
■ Secretion of tears
■ Elimination of tears

9. Secretion of tears
There are mainly two types of secretions produced by main and accessorylacrimal
gland;
■ Basal secretion(Accessorylacrimal gland)
■ Reflex secretion(Main lacrimal gland)
MECHANISM
■ Afferent pathway for secretion of tearfilm is contributedby fifth nerve
■ Efferent pathway for secretion is contributed by parasympathetic nerve fibers

11. When the eyelid close;
■ Contraction of pretarsal orbicularis oculi
■ Compression of ampulla and shorteningof canaliculi
■ Result in movementof tear fluid from here to lacrimal sac
■ Contraction of presentation fibers of orbicularis distend the sac and create a
negative pressurewhich draws tear from canaliculi to lacrimal sac

12. When eyelids are open;
■ Relaxation of pretarsal orbicularis allow canaliculi and ampulla reopens and draws
tear from lacus lacrimalis and marginal tear strips
■ Relaxation of preseptal fibers (Horner’s muscle)resulting in the collapse of sac and
a positive pressureis created which forces the tear down to NLD into the nose
■ Gravity also helps to the draining of tears to nose

13. THANK YOU
Have a nice day