Theory

Question 1

Why the cornea is transparent?

Answer 1

lattice arrangement of collagen fibrils producing destructive intereference. tight epi cells with uniform index of rectraction

Question 2

Water content of stroma

Answer 2

78%

Question 3

Average thickness of epithelium

Answer 3

50 microns

Question 4

residual stromal bed - how much to leave

Answer 4

300 microns

Question 5

average endothelial cell count of a young adult

Answer 5

3000 cells per square mm2

Question 6

Manual keratometer reads

Answer 6

4 points of the central 3.2 mm zone

Question 7

Minimal acceptable endothelial cell density for KP

Answer 7

2000 cells per square mm2

Question 8

Endothelial cells count at birth

Answer 8

4000 cells per square mm2

Question 9

Endothelial cells count at 60yo

Answer 9

2500 cells per square mm2

Question 10

Endothelial cells count - trouble for cataract surgery

Answer 10

1000 cells per square mm2

Question 11

How many limbal stem cell population must be intact to maintain normal ocular surface

Answer 11

25-33%

Question 12

What is responsible for increased immune response in corneal transplants?

Answer 12

increased production and secretion of VEGF

Question 13

instantaneous map - other name, feature

Answer 13

tangential/meridional. better estimation of peripheral cornea

Question 14

better estimation of peripheral cornea

Answer 14

instantaneous/tangential/meridional map

Question 15

axial power map - other name, feature

Answer 15

sagittal curvature map. better estimation of central corneal power

Question 16

By what percentage does the corneal thickness have to increase before Descemet’s folds are seen?

Answer 16

10%

Question 17

Corneal thickness when epithelial edema occurs

Answer 17

700 microns

Question 18

Central corneal thickness - greater risk for symptomatic edema after intraocular surgery

Answer 18

640 microns

Question 19

Specular microscopy - mean cell size

Answer 19

150-350 microns2

Question 20

Specular microscopy - coefficient of variation (CV)

Answer 20

SD of mean cell area divided by mean cell area. how variable cell size is

Question 21

Polymegathism

Answer 21

CV>0.4

Question 22

Pleomorphism

Answer 22

lower percentage of hexagonality. <50%

Question 23

What are the major proteoglycans of the cornea? And where are they?

Answer 23

dermatan and keratan sulfate. More in posterior than anterior stroma

Question 24

What is the average dioptirc power of the cornea?

Answer 24

43.25

Question 25

Which cells produce lactoferrin?

Answer 25

lacrimal gland acinar cells

Question 26

What part of the cornea is abnormal when Waite-Beetham lines are present?

Answer 26

deep stroma. it’s in early edema

Question 27

Point located at the intersection of the line of fixation and the corneal surface

Answer 27

Corneal vertex

Question 28

Corneal vertex

Answer 28

Point located at the intersection of the line of fixation and the corneal surface

Question 29

Highest point of the cornea

Answer 29

Corneal apex

Question 30

Corneal apex

Answer 30

Highest point of the cornea