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OD1 - Integrated Ophthalmic Sciences & Preclinical Optometry > BS - Cornea Structure and Metabolism Part 1 - Week 2 > Flashcards

BS - Cornea Structure and Metabolism Part 1 - Week 2 Flashcards

1
Q

What effect does aging have on transmittance?

A

Decreases with age.

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2
Q

Are corneal nerve myelinated?

A

Not entirely, they are unmyelinated within the avascular region.

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3
Q

Does the cornea have blood vessels?

A

No, it will is certain diseased corneas, transplant needed if so.

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4
Q

Define transparency.

A

Quality or state of transmitting light without appreciable scatter.

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5
Q

At what wavelength of light does transmittance increase rapidly?

A

300nm

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6
Q

Is the epithelium of the cornea pigmented?

A

No, unpigmented.

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7
Q

Does the cornea have cells?

A

Very few cells are present here.

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8
Q

How is transparency achieved in the cornea?

A

Precise organisation and separation of stromal collagen fibres in the ECM.

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9
Q

How is precise fibre separation in the corneal ECM maintained?

A

A highly specialised inter-fibrillar matrix is used to maintain it.

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10
Q

Do the collagen fibril diameters vary in the cornea?

A

No, there is minimal variation.

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11
Q

What three factors affect corneal refraction?

A

A stable pre-ocular tear film

Corneal shape - thickness and hydration

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12
Q

Define the layers of the cornea from most superficial, to deepest.

A 
Epithelium
Bowman's layer
Stroma
Dua's layer
Descemet's membrane
Endothelium
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13
Q

How many cells thick is the corneal epithelium?

A

5-6

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14
Q

What is the corneal epithelium continuous with, and where?

A

With the conjunctival epithelium at the limbus.

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15
Q

Describe the cell types of the corneal epithelium.

A

Superficial cells are flattened, non-keratinised squamous cells.
Deepest (basal) cells are columnar.
Wing cells are between basal and superficial cells.

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16
Q

How can one tell between keratinised and non-keratinised epithelial cells?

A

Keratinised cells lack a nucleus, which non-keratinised cells do.

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17
Q

Describe the cycle of a typical corneal epithelial cell, beginning with a basal cell. Define the turnover time for the entire corneal epithelium.

A

As basal epithelial cells age, they migrate upward to the surface, becoming wing cells, then flattened, non-keratinised, squamous cells.
Eventually they lose attachment, and are sloughed off.
Entire corneal epithelium turnover is ~7 days.

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18
Q

What shape do the corneal flattened, non-keratinised, squamous cell nuclei have?

A

They are horizonal.

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19
Q

What is the ery surface of the corneal epithelium like? Why is this so?

A

Surface consists of microvilli and microplicae (folds).

Increases surfae area, which increases tear film stability.

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20
Q

What does the epithelium secrete?

A

Mucins, which contribute to the tear film.

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21
Q

Describe the three kinds of connections that corneal epithelium cells have.

A

Tight junctions - seals with neighbouring cells so water soluble molecules dont leak between cells
Desmosomes - at the apical/basal surfaces of epithelial cells (attach them vertically)
Gap junctions - allows communications between cells.

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22
Q

Does mitosis occur in the epithelium?

A

Very little occurs in the germinal layer.
Only place it occurs in a normal epithelium.
Most mitosis occurs at the limbus.

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23
Q

Is the epithelium stratified?

A

Yes.

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24
Q

What is the corneal epithelium anchored to? What molecules are responsible for this? Which of these molecules form bowmans layer?

A

A basement membrane, and bowmans layer.
Hemidesmosomes anchor the basal layer to the lamina densa via fibrils called lamina lucida.
Anchoring fibrils attach the lamina densa to anchoring plaques.
Bowmans layer is formed of lamina densa, anchoring fibrils, and anchoring plaques.

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25
Q

Are the fibrils within the bowmans layer obviously ordered?

A

No

26
Q

What makes up the basal lamina of bowmans layer, and what can be found deep to it?

A

Lamina lucida, connecting to the lamina densa.

Deep to it are anchoring fibrils and anchoring plaques, which form bowmans zone.

27
Q

What percentage of corneal thickness does the corneal stroma represent?

A

90%

28
Q

What kind of connective tissue is the stroma?

A

Fibrous, dense, reguar

29
Q

Are fibroblasts found within the corneal stroma?

A

Yes, as keratocytes.

30
Q

How are collagen fibril bundles arranged within the corneal stroma?

A

They run parallel to each other.

31
Q

What are collagen bundles within the cornea called?

A

Lamellae

32
Q

How many collagen bundles can be found within the corneal stroma?

A

200-300

33
Q

How are adjacent collagen bundles arranged?

A

Lamellae lie at ordered angles to each other, but collagen fibrils within are parallel.

34
Q

Describe collagen fibril diameter and density within the corneal stroma, limbus, and conjunctiva.

A

Diameter and density are uniform within the stroma.

As the limbus is approached, it rises sharply, and at the conjunctiva, it varies greatly.

35
Q

What maintains the regular arrangement of fibre bundles within the corneal stroma? Are these bundles at orthogonal angles?

A

Keratocytes maintain the order. They are not neccessarily orthogonal.

36
Q

What are corneal stromal collagen fibrils associated with?

A

Proteoglycans.

37
Q

What are collagen fibril diameter and seperation like compared to the wavelength of light, and why?

A

They are both small, to prevent scattering.

38
Q

What is the main type of collagen within the corneal stroma? Name two more types found here.

A

Main - I

Also found are III, V, and VI

39
Q

What hydrated volume do keratocytes compose the corneal stroma?

A

2.5%

40
Q

Are keratocytes evenly distributed throughout the corneal stroma?

A

No, there is a linear reduction going anterior to posterior.

There is evidence of a clockwise spiral of cell bodies from anterior to posterior.

41
Q

What function do keratocytes have?

A

Active contro of stromal remodelling.

42
Q

What happens to fibroblasts/keratocytes if trauma occurs?

A

They can turn into myofibroblasts.

43
Q

Name 2 factors contributing to corneal swelling, and 3 factors contributing against it.

A 
Contribution
-GAGs attracting water with their negative charge
-Intraocular pressure
Against swelling
-Epithelial and endothelial barriers
-Endothelial pumps
-Evaporation
44
Q

Describe the Donnan effect.

A

Major mechanism of water uptake in a charged gel is due to ionic imbalances. Major cause of water uptake into the corneal stroma.

45
Q

Describe volume exclusion, and compare it to the Donnan effect.

A

Small holes within a matrix allow passage of water, but not anything larger. Is slow and minor form of water uptake in the corneal stroma.
Donnan effect is much 600 times faster, and is the major mechanism.

46
Q

Descirbe Descemet’s membrane in terms of the endothelium.

A

It is the basement membrane of the endothelium.

47
Q

What produces Descemet’s membrane, and what happens to it with age?

A

Produced constantly with age, and thickens with age.

48
Q

Describe Descemet’s membrane in terms of its layer thicknesses.

A

Anterior 1/3rd

Posterior 2/3rds

49
Q

What collagen type forms Descemet’s membrane?

A

Made of a lattice of type IV and VIII

50
Q

Describe Descemet’s membrane anterior/posteriorly in terms of appearance.

A

Anterior - granular

Posterior - homogenous

51
Q

Describe the corneal endothelium, their shape, thickness, and major function.

A

Single layer of flattened hexagonal cells.

Critical to corneal hydration

52
Q

Do corneal endothelial cells have gap junctions?

A

Yes.

53
Q

How does the corneal endothelium contribute to conreal hydration? Is it a permeable membrane?

A

It is a permeable membrane that controls inflow of ions/solutes from the aqueous humour into the stroma.
Has leaky barriers compared to superficial epithelial cells.

54
Q

What happens to the cornea if the endothelium is damaged?

A

It swells

55
Q

Do endothelial cells divide?

A

No, they are lost with age, disease, contact lens wear, and surgery

56
Q

What happens to the corneal epithelium as the limbus is approached?

A

Thickness increases.

57
Q

What happens to lamellar organisation at the limbus?

A

Goes from being orderly to very irregular, forming the sclera.

58
Q

What are the Palisades of Vogt?

A

Radial projections of limbal eipthelium that extend into the cornea, and are spoke-like.
Within these depressions, are a stem cell population responsible for epithelium turnover.

59
Q

What nerve innervates the cornea, and how many branches per cornea? How are the nerves oriented, and are they myelinated?
What do they form when the nerves reach bowmans layer? What arrangement does it have?

A

70-80 branches of long ciliary nerves. They enter the limbus radially and lose their myelin sheath. Stromal nerve fibres turn abruptly 90 degrees and proceed towards the corneal surface.
They pierce bowmans layer, and form the subepithelial nerve plexus, which is whorl-like.

60
Q

Where are the majority of corneal nerves found? Describe their density throughout the entire scornea.

A

Majority found in the anterior stroma.

Few are in the posterior stroma, and none in Descemet’s membrane or the endothelium.

61
Q

Which collagen type is vital to corneal organisation?

A

Type V

OD1 - Integrated Ophthalmic Sciences & Preclinical Optometry (123 decks)

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