Applied anatomy & physiology of the eyes

Question 1

Staring at the green box, identify each part of the eye

Answer 1

Note the ‘Fovea’ is part of the Macula (but the names are used interchangeably)

Question 2

What are the 3 coats (Tunics) of the eye?

What parts of the eye make up each layer

Answer 2

Fibrous coat:

• Cornea, sclera

Vascular coat

• Iris, Ciliary body, choroid

Sensory coat

• Retina

Question 3

What is the cornea?

Answer 3

The transparent front part of the eye that covers the iris, pupil, and anterior chamber.

The cornea, with the anterior chamber and lens, refracts light, with the cornea accounting for approximately two-thirds of the eye’s total optical power.

Question 4

What is the sclera?

Answer 4

The opaque, fibrous, protective, outer layer of the human eye containing mainly collagen and some elastic fibres

Question 5

Briefly describe each of the layers that make up the vascular coat of the eye

Answer 5

Iris:

• Thin contractile diaphragm which regulates the amount of light reaching the retina

Ciliary body:

• Part of the eye that includes the ciliary muscle, which controls the shape of the lens, and the ciliary epithelium, which produces the aqueous humor

Choroid:

• Dark red/brown layer between the sclera and retina
• Basically just where all the blood vessels are
• Continous anteriorly with Ciliary body

Question 6

What is aqueous humor?

Answer 6

A transparent, watery fluid similar to plasma, but containing low protein concentrations.

It is secreted from the ciliary processes

Contained in both anterior and posterior chambers of the eye (but not the vitreous humour bit)

Question 7

What is vitreous humor?

Answer 7

Clear gel that fills the space between the lens and the retina

Question 8

Shown below is the histology of the cornea

Identify and describe the layers numbered

Answer 8

1) - Non-keratinised stratified squamous epithelium
2) - Bowman’s membrane (basement membrane)
3) - Stroma

• Regularly arranged collagen
• No blood vessels

4) - Descemet’s layer
5) - Endothelium (single layer) - 2500 cells mm^-2

Question 9

What is this method of investigation shown below

Identify the labels if you please

Answer 9

Slit lamp

Question 10

How does the cornea maintain its transparency?

Answer 10

Stroma (3):

• Regularly arranged collagen = more transparent than irregular
• No blood vessels to get in the way of light

Endothelium cell layer (5):

• Has pumps to actively keep aqueous humor out
  
  • Damage to epithelium = AH gets in and cornea becomes swollen & opaque

Question 11

Why is the cornea described as ‘immune-privileged’ and how does this benefit corneal transplant surgery?

Answer 11

Cornea is avascularised (nae blood vessels)

As blood is such an important transport route for WBCs n stuff = lesser chance of foreign antigens from a corneal graft being recognised by the recipient, so lesser chance of a graft rejection

Question 12

What is Schlemm’s canal?

Answer 12

Circular lymphatic-like vessel in the eye that collects aqueous humor from the anterior chamber and delivers it into the episcleral blood vessels via aqueous veins

Found where the cornea & sclera join

(remember the eye doesn’t have lymph)

Question 13

What is trabecular meshwork?

Answer 13

Area of tissue at the base of the cornea (beside Schlemm’s canal)

Responsible for draining the aqueous humor from the eye (via the anterior chamber) by yeeting it to Schlemm’s canal

Question 14

Identify le stuff

Answer 14

Question 15

Describe the innervation of the cornea

Answer 15

Innervated through the Ophthalmic nerve (CN V₁)

Incredibly sensitive to touch

Responses to foreign bodies (dust etc) will elicit blinking, tears, pain

Question 16

Shown below is the Retina

Identify the boxes and identify the section of the eye below the retina in the diagram

Answer 16

Layer below is the Choroid

Question 17

What is the purpose of the pigmented epithelial layer?

Answer 17

Reinforces the light-absorbing function of the Choroid by reducing the scattering of light

It is a single layer of cells

Question 18

Shown below are a rod and cone

1 - Describe their functional difference.

2 - Identify which one is which.

3 - Identify the labels.

Answer 18

Rods:

• provide vision during dim light or night also known as scotopic vision
• much more sensitive to photons

Cones:

• provide vision during day time or at bright light also known as photopic vision

Question 19

Describe the vasculature of the Choroid and the retina

Answer 19

Choroid is made up of fenestrated blood vessels of varying diameter.

These supply the outer layers of the retina with blood by diffusion.

(The inner layers of the retina get blood from branches of the central retinal artery.)

Question 20

This photo was taken through an ophthalmoscope

Which eye is this?

What is the arrow pointing at?

Answer 20

Left eye (optic disc is on left)

Fovea centralis

Question 21

How is the Fovea Centralis different from the rest of the retina?

Answer 21

Its packed with Cones so has maximum visual acuity

Question 22

What is the Lens of the eye?

Answer 22

Transparent, crystalline biconvex structure

Suspended by zonules from the ciliary body.

It can change shape (i.e. become less or more convex.)

Question 23

As we know, for many structures in the eye, they are avascular in order to be as transparent as possible

The lens is an example of this.

What problems are linked to the lens being like this?

Answer 23

avascularity is one of the factors that predispose it to become opaque later in life

(Cataracts)

Question 24

What thingy is this?

Answer 24

Lacrimal sac

the upper dilated end of the nasolacrimal duct, and is lodged in a deep groove formed by the lacrimal bone and frontal process of the maxilla

Question 25

Describe how tears are formed and drained from the eye

Identify the labels for extra points

Answer 25

Lacrimal gland produces tears

Tears drained into the puncta and move through canaliculi into lacrimal sac

Question 26

What is the tear film?

Answer 26

Thin fluid layer that covers the outer mucosal surfaces of the eye

Question 27

What is the structure of the tear film?

Answer 27

Composed of 3 layers

• Outer, Oily layer (smallest <1%)
• Middle, aqueous layer (largest 69% hehe)
• Inner, mucinous layer that overlies the corneal epithelium (30%)

Question 28

What are the functions of the tear film?

Answer 28

• Keep cornea MOIST
• Wash away particulate foreign bodies
• Contain antibodies and lysozymes to kill microbes
• Smooths outer surface of cornea providing smooth surface for refraction

Question 29

How is secretion of tears into conjunctival sac controlled?

Answer 29

Parasympathetic control via CN VII (facial nerve)

Question 30

Describe how the state of the tear film will stimulate blinking?

Answer 30

Eyes open:

• Middle watery layer of tear film evaporates
  
  • Oily layer gets close to mucinous layer
    
    • When they touch, the film breaks
      
      • This stimulates blinking