Tear film, the globe and cornea

Question 1

What are the 3 components to tear film?

Answer 1

Aqueous layer
Mucin layer
Lipid layer

Question 2

What produces the lipid layer of tear film? Where are these located?

Answer 2

Meibomian/tarsal glands

Tarsal plate in eyelids

Question 3

What is the function of the lipid layer of tear film?

Answer 3

Reduces evaporation

Hold tears within palpebral fissure

Question 4

The mucin layer is mixed into which other layer? What does it do?

Answer 4

Mixed into aqueous layer

Helps stabilise it

Question 5

What produces the mucin layer of tear film?

Answer 5

Goblet cells in conjunctiva

Question 6

What produces the aqueous layer of tear film?

Answer 6

Lacrimal and nicititans gland

Question 7

What is the function of the aqueous layer?

Answer 7

Lubricate, protect and provide nutrition

For corneal, limbal and conjunctival epithelium

Question 8

What control is tear film under? (Nervous system)

Answer 8

Autonomic

Question 9

What nerve mainly supplies tear film production?

Answer 9

Lacrimal nerve of ophthalmic branch of trigeminal

Question 10

Where is the main lacrimal gland located?

Answer 10

Dorsolateral orbit

Question 11

What do the lacrimal puncture open into?

Answer 11

Lacrimal canaliculi

Question 12

What encircles the lacrimal canaliculi and why?

Answer 12

Obicularis oculi

Pumps tears along tear duct system

Question 13

Where do the lacrimal canaliculi meet? Where is this located? Which species is this poorly developed?

Answer 13

Lacrimal sac
Located in lacrimal fossa of lacrimal bone
Poorly developed lacrimal bone in cat and dog

Question 14

Where does the lacrimal sac empty into? Where does this empty into?

Answer 14

Nasolacrmal duct

Nasal cavity

Question 15

The obicularis oculi muscle controls blinking. What is the function of blinking?

Answer 15

Spread tear film

Help drain nasolacrimal gland (pumps tears along duct system)

Question 16

Give 3 reasons why rabbits have a vulnerable lacrimal drainage system

Answer 16

Runs over cheek teeth (dental disease damages nasolacrimal duct)
Only one lacrimal punctual
2 sharp bends in the duct = block easily

Question 17

The globe/eyeball shape varies between species. What shape globe do cattle and horses have?

Answer 17

Slightly flattened

Question 18

What are the 3 layers to the globe/eyeball?

Answer 18

Fibrous layer
Uvea
Neural layer

Question 19

What is the function of the fibrous layer of the globe?

Answer 19

Supports shape of eyeball

Question 20

What is the function of the uvea?

Answer 20

Provides nutrition

Alters light transmission

Question 21

What is within the neural layer of the globe?

Answer 21

Retina = light detection

Question 22

What divides the eye into anterior and posteior segments?

Answer 22

Lens

Question 23

The anterior segment of the globe is further divided into anterior and posterior chambers. What divides these?

Answer 23

Iris

Question 24

What is the outermost layer of the front of the eye? What does it do? Does it have conjunctiva?

Answer 24

Cornea

Dome shape focuses vision No

Question 25

What are the 4 layers of the cornea?

Answer 25

Anterior epithelium Stroma Descemet's membrane Endothelium

Question 26

What does the anterior epithelium of the cornea contain?

Answer 26

Squamous cells at surface Columnar cell at base Lots of pain receptors

Question 27

What does the stroma of the cornea contain?

Answer 27

Collagen fibrils - form lamellae Keratocytes Proteoglycans Pressure receptors

Question 28

What gives the cornea its clarity?

Answer 28

Collagen fibrils that form lamellae in the stroma

Question 29

What produces Descemet's membrane?

Answer 29

Endothelium

Question 30

What dess the endothelium of the cornea do?

Answer 30

Produces Descemets membrane | Maintains stromal hydration

Question 31

Is the endothelium of the cornea able to regenerate?

Answer 31

No | Except in rabbit

Question 32

Damage to the cornea is painful as it is highly innervated. What nerve innervates it?

Answer 32

CN V (trigeminal)

Question 33

Where are pain receptors and pressure receptors in the cornea?

Answer 33

Pain receptors in anterior epithelium | Pressure receptors in stroma

Question 34

How does damage to the epithelium or endothelium cause prevention of light transmission and cause ulcers?

Answer 34

Allows fluid to enter the stroma | Corneal oedema disrupts lamellae

Question 35

Does the epithelium of the cornea heal well after damage? How?

Answer 35

Yes | By neighbouring cells, stem cells at limbus and mitosis

Question 36

What happens when the cornea is damaged?

Answer 36

Neovascularisation = blood vessels grow from limbus to aid healing

Question 37

When the cornea is damaged, neovascularisation occurs. It can be superficial or deep. Where do these new vessels come from?

Answer 37

``` Superficial = from conjunctiva blood vessels Deep = ciliary plexus ```

Question 38

What happens to blood vessels from neovascularisation after corneal damage has healed?

Answer 38

Vessels narrow Leave ghost vessels May cause pigmentation