Corneal Transparency

Question 1

Which three tissues are the only transparent tissues in the body

Answer 1

Cornea, crystalline lens, vitreous.

Question 2

7 contributions to corneal transparency

Answer 2

1. Avascular- Lack of blood vessels
2. Amelanotic- Lack of melanocytes centrally and mid-peripherally
3. Lack of myelin sheath surrounding nerves in the cornea
4. Smooth epithelial surface- overlying tear film fills in slight irregularities between cells.
5. Large amounts of water soluble proteins (crystalline) in corneal cells enables cytoplasm to appear homogenous.
6. Highly organized stroll collagen fibrils.
7. Maintenance of 78% water content in the storm. Allows for uniform spacing between collagen fibrils.

Question 3

Difference between Goldman and Bendek’s theory of corneal transparency and Maurice’s lattice theory of corneal transparency

Answer 3

Goldman and Bendek- They think the clarity of the cornea is due to uniform SPACING between fibrils.

Maurice’s- Think the clarity of the cornea is due to uniform DIAMETER.

Question 4

How does the direction of collagen change per layer?

Answer 4

Adjacent layers have perpendicular collagen layers.

Question 5

Factors that increase water content in the stroma

Answer 5

1. Desmosomes between endothelial cells
2. Stromal swelling pressure
3. Intraocular pressure

Question 6

How do desmosomes between endothelial cells increase water content in the stroma?

Answer 6

Desmosomes are found between adjacent cells and allow the entrance of nutrients between. Nutrients from the aqueous humor will flow through the desmosomes to enter the corneal stroma.

Question 7

How does the stromal swelling pressure (SP) affect water content in the stroma?

Answer 7

SP increases water content in the stroma.
SP is the pressure exerted when GAGs/proteoglycans pull water into the corneal stroma. GAGs and proteoglycans are water loving and want more of it inside the stroma!
SP= 55mmHg

Question 8

SP in mmHg

Answer 8

55mmHg

Question 9

How does IOP alter water levels in the stroma?

Answer 9

IOP increases water in the stroma. Pressure exerted from the aqueous humor in the anterior chamber.
Avg is 10-21mmHg

Question 10

Avg IOP

Answer 10

10-21 mmHg

Question 11

Factors that decrease water content in the stroma

Answer 11

1. Tight junctions between epithelial cells.
2. Metabolic pumps in the cell membranes of endothelial cells
3. Metabolic pumps in the cell membranes of epithelial cells
4. Tear film osmolarity

Question 12

How do tight junctions between epithelial cells alter water content in the stroma?

Answer 12

Prevents excessive flow of water from the tear film into the stroma. Forces all molecules, including water, to pass THROUGH the cell membranes.

Question 13

How do metabolic pumps in the cell membranes of epithelial cells alter water content in the stroma?

Answer 13

Ion channels move Na+, Cl- , and K+ in and out of epithelial cells to aid in fluid balance. They will pump ions out of the stroma, into the aqueous fluid, through ATP pumps and water will follow through aquaporins.

Question 14

How does tear film osmolarity alter water content of the stroma?

Answer 14

If your tear film contains a lot of ions, your tear film will be hypertonic (salty tears). This will cause water to exit the corneal epithelium, causing dry eye.

Question 15

Cornea is located between which two fluids

Answer 15

Tear film and aqueous humor