Cornea physiology

Question 1

Normal tear volume?

Answer 1

7-10 ul

Question 2

Average volume of eye drop?

Answer 2

50 ul

Question 3

Normal daily tear production?

Answer 3

2 ml/day (1-2 ul/min)

Question 4

Which is least likely to be found in aqueous component of tears?
A. Lactoferrin
B. Lysozyme
C. MUC5AC
D. Keratoepithelin
E. Secretory IgA

Answer 4

Keratoepithelin

Question 5

3 major components and their sources of tear film

Answer 5

1. Lipid layer: Meibomian glands
2. Aqueous layer: Lacrimal gland
3. Mucin layer: Goblet cells

Question 6

What type of glands are Meibomian glands?

Answer 6

Holocrine glands

Question 7

Components of Mucin tear layer?

Answer 7

1. Large glycoproteins, including MUC5AC (= secreted mucin, from goblet cells)
2. Glycocalyx (membrane bound)

Question 8

Function of glycocalyx

Answer 8

• Converts corneal surface from hydrophobic to hydrophilic
• Prevents bacterial adhesion
• Lubrication

Question 9

Normal corneal endothelial cell count:

1) At birth?
2) In adult?
3) In corneal edema

Answer 9

1) 4000 cells/mm2 (birth)
2) 2000-3000/mm2 (adult)
3) <500-1000 cells/mm2 (corneal edema)

Question 10

Which is least likely to cause superior corneal staining?
A. Sup limbic keratocjitis
B. FB under upper lid
C. Floppy eyelid
D. Neurotrophic keratitis
E. Trichiasis

Answer 10

Neurotrophic (interpalpebral staining)

Question 11

All are true about Rose Bengal except:
A. Stains areas of epi defects and dead epithelial cells
B. Stains epi cells without mucin covering
C. Useful for diagnosing dry eye
D. Useful in diagnosing carcinoma-in-situ
E. Better staining of cornea than conjunctiva

Answer 11

Not diagnostic in carcinoma-in-situ