Introduction to the nervous system - eye

Question 1

Name the 5 layers of the cornea histologically

Answer 1

epithelium - stratified non keratinised squamous 
bowman's membrane 
stroma 
descmet's layer
single layer of squamous endothelium

Question 2

Describe the stroma

Answer 2

regularly arranged collagen fibres

no blood vessels

Question 3

How does the cornea get nutrition?

Answer 3

tear film, aqueous humor and sclera

Question 4

List the 3 ways in which corneal transparency is maintained

Answer 4

histologically - regular collagen arrangement
no blood vessels
endothelial layer pump actively keeps aqueous humor out

Question 5

A break in which layer of the cornea will mean it will heal with scar tissue?

Answer 5

bowman’s membrane

Question 6

What is the advantage of the cornea being avascular?

Answer 6

corneal grafts from donors are less likely to be rejected as the foreign antigens will not be recognised

Question 7

Due to the avascularity of the cornea what is the cornea said to be?

Answer 7

immune privileged

Question 8

How many layers of the retina is there?

Answer 8

10

Question 9

What are layers 1,2 and 9?

Answer 9

1 - pigment endothelium
2 - rods and cones very far back
9 - nerve fibres

Question 10

blood supply - outer and inner layers of the retina

Answer 10

outer - choroid

inner - central retinal artery

Question 11

What about the lens predisposes it to become opacified in later life?

Answer 11

avascular

Question 12

opacification of the lens is called…

Answer 12

cataract

Question 13

How many layers does the tear film have?

Answer 13

3

Question 14

Name the 3 layers of the tear film

Answer 14

mucinous layer
aqueous layer
oily layer

Question 15

What produces each of the 3 layers of the tear film?

Answer 15

mucinous - conjunctiva
aqueous - lacrimal gland
oily - meibomian glands in the tarsal plate

Question 16

What dye can be used to see the tear film?

Answer 16

fluorescein

Question 17

4 functions of the tear film

Answer 17

keeps the cornea moist and prevents drying
washes away foreign bodies
antibodies and lysozymes to kill microbes
smooths outer surface of cornea for refraction

Question 18

What nerve innervates the tear film and is it sympathetic or parasympathetic?

Answer 18

parasympathetic by facial nerve secretes tears into conjunctival sac

Question 19

What causes us to blink?

Answer 19

aqueous layer evaporates and when the oily and mucinous layer come into contact when the tear film breaks down this irritates the eye and causes blinking

Question 20

How often on average do humans blink?

Answer 20

every 7 seconds