cornea sclera part 2

Question 1

what are macula occludens, and what is its function?

Answer 1

they are tight junctions, acts as a leaky barrier between aqueous and stroma.

Question 2

What two factors contribute to the prevention of stromal swelling?

Answer 2

The barrier function of the endothelium,

The pump function of the endothelium

Question 3

What happens to the cornea in cool temperatures?

Answer 3

the cornea swells

Question 4

What inhibits the Na+K+ATPase Pump? and what are its effects?

Answer 4

Ouabain. Stops sodium transport, causes corneal swelling, prevents temperature reversal, and eliminates the transendothelial potential difference

Question 5

True or False: In a wound the endothelial cells do not regenerate.

Answer 5

True. Defects are covered by the spreading of cells from adjacent areas.

Question 6

What is needed for proper corneal function?

Answer 6

Adequate endothelial cell density,

Endothelial cells of uniform size and shape

Question 7

True or False: Pleomorphism is the change in cell size.

Answer 7

False. Pleomorphism is a change in cell shape. Polymegathism is a change in cell size.

Question 8

True or False: LASIK has a significant effect on endothelial cell density.

Answer 8

False. LASIK has NO significant effect on endothelial cell density or percent of hexagonal cells

Question 9

What is CLUE syndrome?

Answer 9

contact lens-use endotheliopathy. Polymegathism reported with long-term use of contact lenses.

Question 10

What innervates the cornea?

Answer 10

ophthalmic division of the trigeminal nerve (via anterior ciliary nerves)

Question 11

What part of the cornea is NOT innervated?

Answer 11

Descemet’s membrane and the endothelium

Question 12

what does the stimulation of nociceptors cause?

Answer 12

stimulation results in the perception of pain

Question 13

What leads to sensory denervation?

Answer 13

Stroke, diabetic neuropathy, and herpes simplex

Question 14

What does sensory denervation cause?

Answer 14

High incidence of epithelial erosions and neurotrophic ulcers

Question 15

Where does the oxygen for corneal metabolism come from? (3 locations)

Answer 15

Atmosphere (mostly),
Aqueous humor,
Limbal vasculature

Question 16

How much oxygen does the epithelium consume compared to the stroma?

Answer 16

Epithelium consumes 10x more O2 compared to the stroma.

Question 17

How much oxygen is delivered to the cornea with eyelids open? closed?

Answer 17

21% with the eyelid open,

8% with the eyelid closed

Question 18

In hard contact lens wearers, how much of the glycogen reserve is used after 8 hrs?

Answer 18

80% of reserve used up in 8 hours of wear

Question 19

What are three symptoms of epithelial edema?

Answer 19

Halo and rainbow formation,
Increased glare sensitivity,
Decreased contrast sensitivity

Question 20

What does lack of vitamin A cause?

Answer 20

Xerophthalmia. Keratinization of the epithelium

Question 21

What is the max amount of cul-de-sac fluid?

Answer 21

20-39 microliters

Question 22

What does the epithelium limit the absorption of?

Answer 22

Limit adsorption of hydrophilic, ionized substances

Question 23

What are ways you can increase drug penetration?

Answer 23

Press on the lacrimal sac;
Use viscous drops, suspensions, ointments;
Slow-release delivery systems;
Contact lenses;
Porcine collagen corneal shields

Question 24

What are Pro and Cons of drug preservatives?

Answer 24

Detergent property:
Pro: Breaks down bacterial cell walls.
Cons: Causes the epithelium and endothelium to be susceptible to damage.

Question 25

What makes up the sclera?

Answer 25

70% water

30% dry weight: collagen fiber, fibroblasts, proteoglycans

Question 26

The sclera is avascular except for what?

Answer 26

superficial vessels of the episclera and the intrascleral vascular plexus

Question 27

Where does the sclera thickness decrease and increase?

Answer 27

decreases towards the equator and increases near the optic nerve

Question 28

how much of the total surface area of the globe is made up of the sclera?

Answer 28

95%

Question 29

Compare scleral fiber diameter and arrangement with the corneal fiber diameter and arrangement.

Answer 29

Scleral fiber diameter ranges from 25-230 nm. Arranged in bundles.

Corneal fiber diameter is uniform at 25 nm. Arranged parallel

Question 30

Form vision deprivation results in what type of refractive error?

Answer 30

Myopia, due to axial elongation of the ocular globe

Question 31

List 3 effects aging has on the sclera.

Answer 31

Progressive degeneration of collagen and elastic fibers,
Loss of GAGs,
Scleral dehydration

Question 32

Name 3 factors that control diffusion rates of drugs to the sclera.

Answer 32

Tissue hydration,
Tissue thickness,
Size and volume fraction of proteoglycans present

Question 33

True of False. Sclera permeability is altered by age.

Answer 33

False. Age, cryotherapy, and diode laser treatment do NOT alter sclera permeability.

Question 34

True or False. Surgical thinning increases permeability of sclera.

Answer 34

True.

Question 35

True or False. the stroma of the sclera is highly innervated.

Answer 35

False. Stroma of the sclera is devoid of innervation, but does allow the passage of nerves.