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272A > L5 Structure of Cornea > Flashcards

L5 Structure of Cornea Flashcards

1
Q

What are the roles of the cornea?

A
  • Major refractive surface of the eye
  • Interacts with the mucin later of the tear film to produce a smooth optical surface
  • Barrier between outside environment (pathogen) and inside
  • Corneal epithelium secretes fluid into tear film - contributes to the removal of fluid from stroma
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2
Q

Describe the structure of the cornea? (ABCDE)

A

Anterior epithelium
Bowman’s membrane
Central stroma
Descement’s membrane
Endothelium

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3
Q

What are the 3 layers of corneal epithelium?

A

Superficial cells, intermediate/wing cells, basal cells

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4
Q

What do the different layers of corneal epithelium represent?

A

Different stages of epithelial terminal differentation

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5
Q

What is the structure of basal cell layer?

A

Single layer of cuboidal cells that sit on bowman’s membrane, capable of division into wing cells

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6
Q

What is the structure of wing cell layer?

A

1-3 cells thick in an intermediate stage of differentation and gives rise to superficial cells.

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7
Q

What is the structure of superficial cells?

A

Terminally differentiated squamous cell that are sloughed off into tears

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8
Q

What is the rate of turnover of corneal epith?

A

7 days

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9
Q

What features of corneal epithelium allows it to carry out its function?

A

Has high resistance tight junctions between superficial cells

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10
Q

What is the X + Y = Z hypothesis

A

Process of differentiation which allows epithelium to turnover every 7 days. Corneal thickness is maintained by a balance between:
- Cell loss from surface (z)
- Proliferation of basal cells (x)
- Central migration of stem cells from limbus (Y)

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11
Q

What does the cornea consist of?

A

Primarily water, ECM, collagen fibrils (mainly 1 and some 5,6), keratocytes

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12
Q

What is the structure of ECM?

A

Made up of proteoglycans which are ladder like attachments along collagen fibrils.

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13
Q

What are the two classifications of proteoglycans in the ECM?

A

Chondroitin/dermatan sulphate and Keratin sulphate

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14
Q

What is the structure of chondroitin sulphate and where is it found?

A

Decorin which binds to type 6 collagen and is abundant in the posterior stroma

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15
Q

What is the structure of keratin sulphate and where is it found?

A

Lumican which is found in the central stroma

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16
Q

How does a high PG content cause high colloid osmotic pressure?

A

It attracts water, which results in the swelling of the stroma and disrupts the spacing of collagen fibrils, causing light to scatter

17
Q

How is the swelling of the stroma counteracted?

A

By active transport of ions by epithelium and endothelium, driving paracellular transport of water out of the stroma.

18
Q

What is the structure of corneal collagen?

A

Lamellar arrangements of collagen fibrils, 200 layers

19
Q

What are keratocytes?

A

Long thin stellate cells which run parallel to corneal surface

20
Q

What do keratocytes do in the cornea?

A

Secrete collagen and is associated with ECM

21
Q

What is the function of the stroma?

A

Transmit light which enters the eyes and scatters less than 10% of light

22
Q

What is the structure of stroma which allows it to scatter less light?

A

Due to arrangement and size of collagen fibrils, it has a lattice structure.

23
Q

Which model explains the non-scattering property of stroma?

A

Light scattering by individual fibrils is cancelled out by destructive interference with scattered light from adjacent fibrils.

24
Q

What does the distance between fibrils and fibril diameter need to be to maintain transparency?

A

Less than one half of the wavelength of light

25
Q

What is the structure of endothelium?

A

Single layer of haxagonal, cuboidal cells attached to the descement’s membrane

26
Q

What is the function of endothelium?

A

Maintain stroma hydration

27
Q

Why does the endothelium contain a high amount of ATP?

A

Contains lots of mitochondria which produce ATP for ion pumps to maintain hydrations

28
Q

Where does the endothelium receive nutrients and oxygen from?

A

Nutrients from aqueous humor, oxygen from tears

29
Q

How does the thickness of endothelium and descement’s membrane change with age?

A

Endothelium layer becomes thinner, descement’s membrane thickens

30
Q

What happens when the endothelium layer gets damaged?

A

Swells up to cover injured areas

31
Q

What is the number of corneal endothelium cells?

A

500,000 non-mitotic cells with limited replacement.

32
Q

Is the cornea supplied with nerves?

A

Yes, it is the most sensitive part of the body. But, deep stroma has no nerves

33
Q

Which ciliary nerves supply the cornea and where do they originate from?

A

Long ciliary nerve originates from opthalmic branch of trigeminal nerve
Short ciliary nerve formed by branches of ciliary ganglion

272A (13 decks)

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