Tear Film Components

Question 1

Name the tear film components.

Answer 1

Lipid layer - outermost
Aqueous Layer - middle
Mucin Layer - innermost

Question 2

List the functions of the tear film.

Answer 2

1. Protect and lubricate the eye
2. Washes away foreign particles
3. Reduces risk of infection
4. Keeps the surface of the eye smooth and clear

Question 3

What does the lipid layer consist of ?

Answer 3

Free fatty acids
Cholesterol
Phospholipids
Wax esters

Question 4

What are the components of the lipid layer secreted by?

Answer 4

Mainly the Meibomian gland , but also the glands of Zeis and Moll.

Question 5

Where is the Meibomian Gland located?

Answer 5

Tiny oil glands which line the margin of the eyelids.

Tarsal plate of the upper and lower eyelids

Question 6

List the functions of the lipid layer .

Answer 6

1. Provide lubrication for smooth eyelid movement
2. Seal the tear film to reduce / prevent evaporation of natural tears
3. Lowers surface tension

Question 7

What does the Aqueous layer consist of ?

Answer 7

Inorganic salts
Glucose
Enzymes
Antibacterial substances such as lysosomes

Question 8

What is the function of lysosomes?

Answer 8

Destroy invading viruses and bacteria .

If cell is damaged or beyond repair , lysosomes help it self destruct - a process called apoptosis

Question 9

List the functions of the aqueous layer.

Answer 9

1. Oxygen supply to the cornea
2. Removes debris and washes it away
3. Creates an optically smooth surface by eliminating minor surface irregularity

Question 10

What is the aqueous layer secreted by?

Answer 10

Lacrimal glands and accessory lacrimal glands

Question 11

Where is the lacrimal gland located?

Answer 11

Under bony bit of eyebrow towards temporal side

Question 12

What is attached to the lacrimal glands ?

Answer 12

Excretory lacrimal ducts

Question 13

Explain how the mucin layer is attached to the corneal epithelial surface

Answer 13

Corneal layer - hydrophobic
It consist of microvilli which project outwards from the surface
Goblet cells from the conjunctiva produce mucous , which migrate across the epithelial surface . The mucous coats and bonds to the epithelial microvilli comprising of glycocalyx
Once the mucous layer has dispersed across the surface the cornea becomes hydrophilic ( water attracting )

Question 14

List functions of the mucin layer

Answer 14

Provides lubrication

Creates hydrophilic surface

Question 15

What does a normal tear function require ?

Answer 15

Normal blink reflex
Normal lid aposition
Normal corneal epithelium