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cornea Flashcards

(68 cards)

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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
how lamella makes cornea clear
-run parallel to corneal surface -in lamellae, fibril parallel, uniform size, spacing -> destructive interference -adjacent lamella is perpedicular to each other
26
how lamella is different in limbus
circumferentaial arrangement
27
what is proteoglycan
central core protein + glycosaminoglycan
28
why proteoglycan is important for cornea
-have strong negative charge + attracts water -water + proteoglycan = gel
29
what is keratocyte, role, location, density
-flat fibroblast cell -maintain collagen fibril and proteoglycan -between stromal lamella -dense in superficial periphery
30
what is pre-descemet's membrane
-part of posterior stroma -adjacent to descemet's membrane -acellular, tough, have lamella -biochem strength of cornea
31
what is descemet's membrane
-highly elastic -basement membrane for "endothelium" -birth 3-4 micron -adult 10-12 micron
32
what is endothelium of cornea*
-only one layer of squamous cell -mosaic polygonal cells
33
what is the role of endothelium of stroma*
-secrete descemet's membrane -maintain hydration
34
how endothelium change through life *
-decrease -remaining cell slide and expand to maintain mosaic model -not regular arrangement anymore
35
what is the variation in cell size and cell shape caleld in endothelium
size: polymegthism shape: pleomorphism
36
what is corneal guttatta
age-related thickening of descemet's membrane
37
corneal innervation *
-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
coneal vasculature *
no blood supply - anti-angiogenic factors
39
how cornea adjacent with other structures?
corneal epithelium - bulbar conj epi corneal stroma - scleral stroma
40
what is the termination of descemet's membrane and endothelium
Schwalbe's line
41
what is palisade of Vogt and where
-ridges of epithelium + fibrovascular tissue -have stem cell -in superior and inferioir limbus
42
overview function of epithelium, anterioir limiting lamina, stroma, posterior limiting lamina and endothelium
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
cornea tissue mechanics*
tensile stregth (ยืดหด) -high tensile strength bc stroma extensibility -no linear elastic shear strength (sliding or bending) -low shear strength
44
what is the normal hydration of cornea
78%
45
why maintaining hydration is important in cornea
to maintain thickness and transparency
46
what pressure regulate stromal hydration*
* Stromal swelling pressure * Epithelial and endothelial barriers * Endothelial pump * Evaporation * Intraocular pressure
47
stroamal swelling pressure*
proteoglycan tend to draw water into stroma
48
epithelial and endothelial barrier*
-opposite to stromal swelling pressure -bc tight junction -endothelium is leaky
49
endothelial pump*
-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
evaporation*
draw water from cornea
51
IOP*
influence only very high or low IOP
52
what is the relationship of thickness and corneal hydration
more hydration, thicker
53
why measuring corneal thickness is important
assessing cornea metabolic integrity
54
what are three metabolic pathway in cornea*
-anaerobic glycolysis -kreb cycle -hexose monophosphate shunt
55
how does corneal swelling occur and what is the consequence
* Minimum oxygen requirement to prevent corneal swelling ~ 10% * Corneal swelling → stromal haze * Hypoxia -> endothelial blebs
56
how waste travel in cornea
* CO2 diffuses easily across epithelium and endothelium * Lactate diffuses slowly across endothelium
57
what contribute to the transparency of cornea*
absorption light scattering Lattice theory cellular layer
58
transparency - absorption
-transmit 90% of light -<300 and >1400 nm is absorbed
59
transparency - light scattering
-no blood vessel, no nerve
60
transparency - Lattice theory
-regular arrangement of lamella, spacing, and diameter -> destructive interference = Lattice theory
61
transparency - cellular layer
-uniform refractive index bc cellular arrangement
62
corneal innervation
sensory -mechanical stimuli-> pain -thermal reflex blink and larimation
63
what measure corneal sensitivity
aethesiometer
64
where is the highest and lowest sensitivity
-corneal apex highest -fornical conjunctiva lowest
65
what can affect corneal sensitivity
age, dark iris color, contact lens wear
66
how epithelium repair wound
* Mitosis temporarily shuts down * sheet- like movement * Increased rate of mitosis resulting in landslide-like movement
67
how stroma repair wound*
-heal slowly * Newly synthesised collagen lacks regular arrangement of original collagen -scarring
68
how endothelium repair*
* Cells have limited capacity to undergo mitosis * Repaired by cell expansion and migration

opb353-qut (5 decks)

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