Cornea

Question 1

What is the power of anterior corneal surface?
Posterior? Total

Answer 1

Anterior 48.8D
Posteiror -5.8D
Total 43 D

Question 2

What meridian has the shorter radius of curvature?

Answer 2

Vertical meridianWhat are teh layers of the cornea?

Question 3

Where is the cornea steepest?

Answer 3

Centrally

Question 4

refractive index?

Answer 4

1.376

Question 5

What are the layers of the cornea?

Answer 5

EPithelium
Bowman’s membrane
Stroma
Descemet’s
Endothelium

Question 6

How thick is Descemet’s

Answer 6

10um

Question 7

Are junctions tight or loose between endothelium?

Answer 7

Tight to control corneal hydration

Question 8

Where does corneal epithelium get glucose? Oxygen

Answer 8

Oxygen from tear film
Glucose from the stroma

Question 9

Where is most carbohydrate catabolism done in cornea?

Answer 9

Endothelium - rich in mitochondria

Question 10

What happens to lactic acid produced in the cornea?

Answer 10

Diffuses slowly from the stroma and endothelium into the aqueous

Question 11

What % of cornea is water?

Answer 11

75-80%

Question 12

How does IOP affect corneal hydration?

Answer 12

Above 55mmHg can cause corneal oedema

Question 13

What is the predominant type of collagen in thecorneal stroma?

Answer 13

Type I

Question 14

What prvides collages stregth?

Answer 14

Intermolcular cross-links

Hydroxylysineorleucine is the major reducible cross link

Question 15

How does diamater of collagen fibril and spacing change throughout the cornea

Answer 15

Constant

Question 16

What are proteoglycans?

Answer 16

Glycosylated proteins - repeated disaccharides

Bind to collagen fibrils and regulate spacing

Question 17

What is the most common conreal proteoglycan?

Answer 17

Keratan sulphate - 60%

Dermatan - 40%

Question 18

What happens to collagen in corneal scarring?

Answer 18

Width decreases and number of glycoside residues increase - opacity is reduced

Ratio of keratan:dermatan decreases in scars - distortion of regular arrangement of collagen fibrils

Question 19

What are MMPs? What metal?

Answer 19

Matrix metalloproteinases - break down components of extracellular matrix - remodelling after injury

Zn 2+

Question 20

Which MMP is found in helathy cornea? What do they do?

Answer 20

MMP2 - active against Type IV, V, VII collagen

MMP1, 3, 9 after corneal injury

Question 21

What does lactic acid accumulation in the cornea manifest as?

Answer 21

Corneal oedema

SLActatebuilds up due to anaerobic respiration e.g. over wearing of ill fitting contact lenses preventing O2 from tear film

Only small amount of lactate removed through tears, most must diffuse through stroma and endothelium to aq = build up

Osmotic shift pulling water into corneal strome = oedema

Lactate pumped into aq - by H+ lactate pump - increaseed acidification of cornea - potassium loss, cell shrinkage, apoptosis

Question 22

Corneal endothelial cell density in adult

Answer 22

3000cell/mm2

Question 23

How deos the cornea change overnight?

Answer 23

4-8% thicker due to relative hypoxia resulting in swelling

Question 24

What joins the basal columnar layer of the corneal epithelium to the basal lamina?

Answer 24

Hemidesmosomes