OAP - Cornea 1: Shape & Curvature - Topic 4

Question 1

Describe the shape of the cornea

Answer 1

• Cornea is the transparent structure overlaying the iris
• Cornea transmits 95% of light hitting it
  • Protective • Avascular • Highly sensitive

Question 2

Explain why the cornea is the main

refractive structure of the eye

Answer 2

• Transparent
• Transmits light
• Powerful refractive medium
• High optical power
• Shape and topography of cornea is
essential
• Difference in refractive indices

Question 3

How important is the cornea as

a refractive medium?

Answer 3

Most (75%) of the refractive
power in the eye comes from the
cornea
• Cornea optical power = 45D
• Lens optical power = 15D

Question 4

Cornea is composed of 5 layers?

Answer 4

From anterior to posterior the layers of the cornea are:

1. Epithelium
2. Bowman’s layer
3. Stroma
4. Descemet’s membrane
5. Endothelium

Question 5

Describe the purpose of the stratified corneal epithelium

Answer 5

• Barrier function and protection
• protective against chemical and mechanical damage, and water loss

-Together with the tear film, provides optically smooth front surface to cornea

Question 6

How does the anatomy and physiology of the corneal epithelium relate to its purpose?

Answer 6

5-7 cells thick - protection
- Epithelial layer is thicker in the periphery of cornea (near limbus)

Cell Junctions - protection

Stratified non-keratinised epithelium - smooth

Question 7

Explain how the (corneal) epithelium renews itself.

Question 8

What are Basal cells and what are its functions?

Answer 8

• A single layer of columnar cells
• Basal surface attaches to basement membrane (secreted by the basal cells)
• Mitotic layer of cells (REGENeration occurs here)

Question 9

What is the function of the Limbal stem cells?

Answer 9

• a.k.a corneal epithelial stem cells
• Limbal stem cell proliferation has the role of maintaining the cornea; for example, by replacing cells that are lost via tears.

Question 10

Explain how the epithelium renews itself

Answer 10

1) Basal cells transform into wing cells
2) Senescence (deterioration with age)
3) Wing cells transform into squamous cells

4) Shedding,
1. Shed in tear film
2. Apoptosis

5) Proliferation
- Basal
- Limbal Stem cells