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opb353-qut > cornea > Flashcards

cornea Flashcards

1
Q

what are the function of cornea

A
  • Protection – part of
    tough outer coat of eye
  • Optical – provides ~ 2/3rds of eye’s optical power
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2
Q

what is the dimension of cornea - verticala nd horizontal

A

Horizontal 11.7 mm
Vertical 10.6 mm

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3
Q

what is more curved? anterioir central or posterioir central of cornea

A

anterioir central

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4
Q

what is the corneal thickness central vs peropheral

A

central = 0.53mm, peripheral = 0.67mm

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5
Q

how thickness of cornea change overnight

A
  • Overnight corneal swelling of ~5%
  • Returns to baseline 1-2 hours after waking
  • Cornea relatively stable in thickness throughout day
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6
Q

how curvature (anterioir and posteroir is in the morning

A
  • Anterior curvature flattest in
    early morning (~ 0.03 mm)
  • Posterior curvature steeper in early morning (~0.03 mm)
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7
Q

what is the condition of corneal thining

A

keraoconus

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8
Q

give the overview of cornea layer *

A

-epithelium
-anterioir limiting lamina
-stroma
-posterior limiting lamina (descemet’s membrane)
-endothelium

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9
Q

layers of corneal epithelium

A

-squamous cells
-wing cells
-basal cell
-basement membrane

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10
Q

important feature of corneal squamous cell

A

-have tight junction (zonular occluden) near apical surface
-microvilli, microplicae to interact with tear

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11
Q

important feature of wing cell

A

-irregular shape
-concave inferioir surface
-lateral extension (wing!)

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12
Q

important feature of basal cell

A

-single columnar
-germinative layer -> mitotic activity
-produce more cell for epithelum
-synthesise basement membrane

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13
Q

how corneal epithelium proliferate*

A

-new cell produced by mitosis in stem cell in palisade of Vogt
-move from periphery to center of basal cell
-columnar -> squamous as migrate from basal layer to surface
-surface cell shed into tearfilm -> aid by blink
-every 10days

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14
Q

what are types of cell junctions

A

-tight junciton
-interdigitation
-desmosome
-hemidesmosome
-gap junction

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15
Q

where is tight junction and what for

A

-between adjoining squamous cells
-“barrier” to intercellular movement of substance

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16
Q

what is interdigitation, and what for

A

-infolding with adjacent cells
-for strong intercellular adhesion

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17
Q

what is desmosome for

A

-adhesion between adjacent cells

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18
Q

what is hemidesmosome for

A

-attachment fo basal cells to basement membrane +anterioir stroma

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19
Q

what is gap junciton for

A

-channels between cells -> allow passage of ions

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20
Q

what is basement membrane

A

-basal lamina of epithelium
-synthesised by basal epithelial

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21
Q

what are the component of basement membrane

A

lamina lucida (clear zone)
lamina densa (darker zone)

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22
Q

feature of anteriori limiting lamina

A

-acellular region
-randomly oriented fine collagen fibril
-formed and maintain by epithelial cell

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23
Q

feature of stroma

A

-90% corneal thickness
-have collagen (lamella), proteoglycan, keratocyte
-place for nerve innervation

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24
Q

what is lamella *

A

-arrangement of colagen fibril (250-300 layers)

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25
Q

how lamella makes cornea clear

A

-run parallel to corneal surface
-in lamellae, fibril parallel, uniform size, spacing -> destructive interference
-adjacent lamella is perpedicular to each other

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26
Q

how lamella is different in limbus

A

circumferentaial arrangement

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27
Q

what is proteoglycan

A

central core protein + glycosaminoglycan

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28
Q

why proteoglycan is important for cornea

A

-have strong negative charge + attracts water
-water + proteoglycan = gel

29
Q

what is keratocyte, role, location, density

A

-flat fibroblast cell
-maintain collagen fibril and proteoglycan
-between stromal lamella
-dense in superficial periphery

30
Q

what is pre-descemet’s membrane

A

-part of posterior stroma
-adjacent to descemet’s membrane
-acellular, tough, have lamella
-biochem strength of cornea

31
Q

what is descemet’s membrane

A

-highly elastic
-basement membrane for “endothelium”
-birth 3-4 micron
-adult 10-12 micron

32
Q

what is endothelium of cornea*

A

-only one layer of squamous cell
-mosaic polygonal cells

33
Q

what is the role of endothelium of stroma*

A

-secrete descemet’s membrane
-maintain hydration

34
Q

how endothelium change through life *

A

-decrease
-remaining cell slide and expand to maintain mosaic model
-not regular arrangement anymore

35
Q

what is the variation in cell size and cell shape caleld in endothelium

A

size: polymegthism
shape: pleomorphism

36
Q

what is corneal guttatta

A

age-related thickening of descemet’s membrane

37
Q

corneal innervation *

A

-sensory

-long ciliary nerve -> nasociliary nerve, ophthalmic nerve, trigeminal nerve

-some nerve enter mid stroma -> move anterioirly-> anterioir limiting lamina
-> basal epithelial (fine branch) -> surface epithelium

-loss of myelination

38
Q

coneal vasculature *

A

no blood supply - anti-angiogenic factors

39
Q

how cornea adjacent with other structures?

A

corneal epithelium - bulbar conj epi

corneal stroma - scleral stroma

40
Q

what is the termination of descemet’s membrane and endothelium

A

Schwalbe’s line

41
Q

what is palisade of Vogt and where

A

-ridges of epithelium + fibrovascular tissue
-have stem cell
-in superior and inferioir limbus

42
Q

overview function of epithelium, anterioir limiting lamina, stroma, posterior limiting lamina and endothelium

A

epithelium
-mechanical barrier
-optical surface
-barrier to diffusion of water and drug

anterior limiting lamina, stroma
-strength
-shape
-transparency

posterioir limiting lamina, endothelium
-barrier
-hydration

43
Q

cornea tissue mechanics*

A

tensile stregth (ยืดหด)
-high tensile strength bc stroma

extensibility
-no linear elastic

shear strength (sliding or bending)
-low shear strength

44
Q

what is the normal hydration of cornea

A

78%

45
Q

why maintaining hydration is important in cornea

A

to maintain thickness and transparency

46
Q

what pressure regulate stromal hydration*

A
  • Stromal swelling pressure
  • Epithelial and endothelial barriers
  • Endothelial pump
  • Evaporation
  • Intraocular pressure
47
Q

stroamal swelling pressure*

A

proteoglycan tend to draw water into stroma

48
Q

epithelial and endothelial barrier*

A

-opposite to stromal swelling pressure
-bc tight junction
-endothelium is leaky

49
Q

endothelial pump*

A

-enz make ion move from stroma to aqueous -> water go out of stroma
-active transport of HCO3-, Na+, K+
-hydration maintained: pump rate = leak rate

50
Q

evaporation*

A

draw water from cornea

51
Q

IOP*

A

influence only very high or low IOP

52
Q

what is the relationship of thickness and corneal hydration

A

more hydration, thicker

53
Q

why measuring corneal thickness is important

A

assessing cornea metabolic integrity

54
Q

what are three metabolic pathway in cornea*

A

-anaerobic glycolysis
-kreb cycle
-hexose monophosphate shunt

55
Q

how does corneal swelling occur and what is the consequence

A
  • Minimum oxygen requirement to prevent corneal swelling ~ 10%
  • Corneal swelling → stromal haze
  • Hypoxia -> endothelial blebs
56
Q

how waste travel in cornea

A
  • CO2 diffuses easily across epithelium and endothelium
  • Lactate diffuses slowly across endothelium
57
Q

what contribute to the transparency of cornea*

A

absorption
light scattering
Lattice theory
cellular layer

58
Q

transparency - absorption

A

-transmit 90% of light
-<300 and >1400 nm is absorbed

59
Q

transparency - light scattering

A

-no blood vessel, no nerve

60
Q

transparency - Lattice theory

A

-regular arrangement of lamella, spacing, and diameter -> destructive interference = Lattice theory

61
Q

transparency - cellular layer

A

-uniform refractive index bc cellular arrangement

62
Q

corneal innervation

A

sensory
-mechanical stimuli-> pain
-thermal

reflex blink and larimation

63
Q

what measure corneal sensitivity

A

aethesiometer

64
Q

where is the highest and lowest sensitivity

A

-corneal apex highest
-fornical conjunctiva lowest

65
Q

what can affect corneal sensitivity

A

age, dark iris color, contact lens wear

66
Q

how epithelium repair wound

A
  • Mitosis temporarily shuts down
  • sheet- like movement
  • Increased rate of mitosis resulting in landslide-like movement
67
Q

how stroma repair wound*

A

-heal slowly
* Newly synthesised collagen lacks regular arrangement of original collagen
-scarring

68
Q

how endothelium repair*

A
  • Cells have limited capacity to undergo mitosis
  • Repaired by cell expansion and migration

opb353-qut (5 decks)

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