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Ocular Phys > Block 9 > Flashcards

Block 9 Flashcards

1
Q

3 main functions of cornea

A
  • refract light
  • transmit light
  • protect
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2
Q

Factors affecting refraction

A
  • ant curvature
  • ref index from air to TF
  • corneal thickness
  • post curvature
  • ref index from cornea to aqueous
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3
Q

Total power of eye

A

60D

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4
Q

How much of the power of the eye comes from the cornea

A

40-48D

- 2/3 to 3/4 of power

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5
Q

How does the cornea transmit light

A
  • little scattering
  • little distortion
  • max transmission
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6
Q

How much scatter is in the cornea

A

<1%

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7
Q

How does cornea protect long term vision

A
  • TF protect from infection
  • blocks UV light to protect retina
  • hard to penetrate
  • quick healing
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8
Q

How sensitive is the cornea

A

One of the most sensitive in the body

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9
Q

Innervation of cornea

A

Ophthalmic division of trigeminal nerve

- 60-80 long ciliary n.

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10
Q

The cornea is sensitive to

A
  • touch
  • cold
  • chemicals
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11
Q

Normal CV of endothelium

A

.25

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12
Q

Shape of majority of endothelial cells

A

Hexagonal

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13
Q

Does the endothelium regenerate

A

No

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14
Q

What happens as you lose endothelial cells

A

Cell density decreases and cells change shape, becoming less hexagonal

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15
Q

How much of the cornea is the stroma

A

90%

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16
Q

How does cornea maintain transparency

A

Uniform size and spacing of collagen

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17
Q

What is the optimal water level in stroma

A

75-80% water

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18
Q

Which layer is resistant to deformation, trauma and FB

A

Bowman’s layer

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19
Q

Will Bowman’s layer scar?

A

Yes

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20
Q

Thickness of bowman’s layer

A

8-14 microns

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21
Q

(New) Layer between stroma and descemet’s membrane

A

Dua’s layer

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22
Q

How thick is dua’s layer

A

15 microns thick

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23
Q

How does the epithelium help maintain a proper hydration

A

Tight junctions

- keep out water

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24
Q

How does the stroma help maintain a proper hydration

A

Proteoglycans

- pull water in

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25
Q

How does the endothelium help maintain a proper hydration

A

Leaks fluid into cornea

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26
Q

Driving forces of water transport in cornea

A

Cl- extrusion and Na+ absorption

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27
Q

Two ways water moves through cornea

A
  • stroma to endo to aqueous

- epi to TF

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28
Q

Bidirectional water transport channels

A

Aquaporins

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29
Q

What is lost during a minor corneal abrasion

A

Zonula occludens

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30
Q

2 things that happen with a minor abrasion

A
  • edema

- haziness

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31
Q

How does edema affect VA

A

Decrease VA

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32
Q

What happens when there is a more extensive corneal abrasion

A

Fluid gets into the stroma

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33
Q

Fastest healing tissue in the body

A

Cornea

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34
Q

The healing of the cornea relies on

A

Peptide growth factors

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35
Q

How quickly does the cornea heal (minor abrasion)

A

24-48 hours

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36
Q

How quickly can the entire cornea be replaced

A

2 weeks

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37
Q

Which layers of the cornea consume the most oxygen

A

Endo and epi

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38
Q

Which layer of cornea can store glycogen

A

Epi

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39
Q

Compromises the integrity of the epi

A

Corneal ulcer

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40
Q

The epi is impermeable to

A

Ions

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41
Q

Epi and endo are…

A

Hydrophobic

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42
Q

What type of material penetrates the cornea easier

A

Lipid soluble

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43
Q

3 conditions from loss of stability and structure of cornea

A
  • keratoconus
  • ectasia
  • high/low IOP
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44
Q

Corneal thickness at birth

A

Full thickness

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45
Q

Horizontal cornea diameter at birth

A

90% of full size

- 10mm

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46
Q

Axial length of eye at birth

A

2/3 of adult size

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47
Q

Why are kids typically more hyperopic

A

Bc the axial length is shorter at birth and must grow

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48
Q

At what age does the cornea bc adult size

A

3 years

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49
Q

Sclera is growing until what age

A

10-12

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50
Q

Most eyes are emmetropic by what age

A

6-8

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51
Q

When changes happen in central cornea, affecting transparency

A

Dec VA

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52
Q

Cornea aging changes: sensitivity

A

Decreased

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53
Q

Cornea aging changes: scatter

A

Increase

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54
Q

Cornea aging changes: curvature

A

Flattens

- becomes against the rule

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55
Q

Cornea aging changes: descemet’s thickness

A

Gets thicker

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56
Q

Most common aging change

A

Corneal arcus

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57
Q

White ring formed by cholesterol deposits in peripheral stroma

A

Corneal arcus

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58
Q

Corneal arcus is most common is what pt age range

A

60-80

59
Q

What is suspected if a pt under 40 has corneal arcus

A

Hyperlipidemia

60
Q

Corneal arcus: bi or unilateral

A

Bilateral

61
Q

What layer is affected in corneal arcus

A

Bowman’s

62
Q

What happens to the epi with age

A

Loss of intracellular junctions causing dec barrier function

63
Q

Horizontal pigmented line at lower lid margin

A

Hudson-stahli line

64
Q

What age does the hudson-stahli line appear

A

After 50

65
Q

What causes the Hudson-stahli line

A

Iron deposits in epi cytoplasm (basal cells)

66
Q

Degeneration of bowman’s

A

Limbal girdle of vogt

67
Q

Yellowish/white opacity at 3 and 9 o’clock

A

Limbal girdle of vogt

68
Q

What appear in the periphery due to changes in descemet’s membrane with age

A

Hassall-henle bodies

69
Q

Which illumination will you see descemet’s warts

A

Retro

70
Q

Endo cell density with age

A

Decreases

71
Q

Avg endo cell density in kids

A

4000 cell/mm^2

72
Q

Avg endo cell density in adults

A

2500 cell/mm^2

73
Q

How does the cell density change over times (numerically)

A

Dec .6-1% per year

74
Q

Greater than normal variation in size of endo cells

A

Polymegathism

75
Q

Increased variability in size and shape of endo

A

Pleomorphism

76
Q

Vertical line on posterior pole

A

Krukenberg’s spindle

77
Q

Why is there a dec in corneal sensitivity with age

A

Loss of corneal nerves

78
Q

Refractive error is due to what 2 factors

A
  • axial length

- corneal curvature

79
Q

Myopic eye length

A

Longer

80
Q

Hyperopic eye length

A

Shorter

81
Q

Development of myopia usually occurs around what age

A

8-14

82
Q

What is myopia caused by

A

Poor image quality sends signal to sclera to move to get the retinal in the proper spot for a clear image
- lengthening of posterior eye

83
Q

Increased outdoor activity does what to your chances of myopia

A

Reduced risk of myopia

84
Q

Closer to the equator – more or less myopia

A

Less myopia

85
Q

Scleral remodeling in myopia

A

Thinning

86
Q

As the sclera thins, mainly at posterior pole, tissue can bulge out

A

Ectasia

87
Q

Why can the sclera become yellow with age

A

Fatty deposits

88
Q

Why does sclera become thin and lose elasticity with age

A

Degeneration of collagen and elastic fibers

89
Q

3 biomolecules involved in corneal wound healing

A
  • integrins
  • cytokines
  • growth factors
90
Q

Sense changes in extracellular environment

A

Corneal integrins

91
Q

Control growth of corneal cells

A

Cytokines

92
Q

Maintain transparency and induce migration

A

Growth factors

93
Q

How many cells thick is the epi

A

5 - 7

94
Q

3 layers of epi

A

Surface
Wing
Basal

95
Q

How many cells thick is the surface layer of the epi

A

2

96
Q

How many cells thick is the wing layer of epi

A

2-3

97
Q

How many cells thick is the basal layer of epi

A

1

98
Q

Which layer of the corneal epi has cells that divide

A

Basal

99
Q

How does the epi replace itself

A
  • Stem cells from the periphery divide
  • cells move to become basal
  • then move to become wing, then surface
  • surface cells shed into TF

**7 day turnover

100
Q

Time frame for small corneal lesion to heal

A

24-48 hours

101
Q

If the basement membrane is damaged, how long does it take for corneal to heal

A

Several months

102
Q

Does the cornea scar

A

Usually not

103
Q

Corneal epithelium sloughs off bc of poor adhesion (between epi and basement or between basement and underlying tissue)

A

Recurrent corneal erosion

104
Q

Does bowman’s layer regenerate

A

No

105
Q

Bowman’s layer is composed of

A

Collagen

106
Q

90% of corneal thickness

A

Stroma

107
Q

Stroma is composed of what 3 things

A

Collagen, keratocytes, ground substance

108
Q

How long for stroma to reach full strength after wounded

A

Months

109
Q

How are wounds healed in stroma

A
  • Keratocytes become myofibroblasts
  • regenerated collagen is larger and less precisely organized
  • myofibroblasts back to keratocytes by apoptosis
110
Q

Descemet’s mem healing is regenerated by

A

Keratocytes and endo

111
Q

Single layer of flat cells

A

Endo

112
Q

Cells of endo are known as

A

Polyhedral

  • 70-80% hexagonal
  • 20-30% heptagonal
113
Q

Would healing of endo

A

Neighboring cells enlarge, cells remodel, inc number of ion pumps

–> doesn’t create new cells

114
Q

Most glucose comes from

A

Aqueous humor

115
Q

Minor glucose supply

A

TF and limbal capillaries

116
Q

Glycolysis - 1 glucose gives how much ATP (net)

A

2

117
Q

Krebs and ETC produce how much ATP

A

36

118
Q

Which 2 layers will consume oxygen

A

Endo and epi

119
Q

Where does the epi get oxygen

A

Limbal vasculature and TF (atmosphere - 155 mmHg)

120
Q

Where does endo get oxygen

A

Aqueous (40mmHg)

121
Q

Aerobic metabolism deals with which cycle

A

Krebs

122
Q

Anaerobic metabolism deals with which cycle

A

Glycolysis and HMP shunt

123
Q

Produces amino acids and intermediates for nucleotide prod (for DNA replication)

A

HMP shunt

124
Q

Important for the production of components required for rapid regeneration of corneal epithelial cells

A

HMP shunt

125
Q

In anaerobic conditions, what builds up

A

Pyruvate, which is converted to lactic acid

126
Q

What does lactate buildup do

A

Induces epi and stroma edema

127
Q

Situations that can cause too much time in anaerobic conditions

A
  • CLs wearers

- lots of sleep

128
Q

Painful condition caused by exposure to UV rays (natural or artificial sources)

A

Photokeratitis or UV Keratitis

129
Q

Low exposure to UV

A

Inhibited cell mitosis

130
Q

Medium to high exposure to UV

A

Swollen nuclei and cell death

131
Q

Extreme UV exposure

A

Complete sloughing of epi cells

132
Q

What also contributes to damage at the higher levels of UV damage

A

oxygen

133
Q

UV light damage causes what dimers

A

Thymine (pyramids)

- cant replicate DNA

134
Q

DNA repair enzyme

A

UV-specific endonuclease

exinuclease

135
Q

Process of DNA repair from UV damage

A
  • Exinucleause cuts DNA on both sides of damage
  • remove damage
  • gap filled by DNA Pol 1
  • DNA ligase complete the bond
136
Q

Deficiency in the excision endonuclease and a reduced ability to repair damage from UV light

A

Xeroderma pigmentosum

137
Q

Symptoms of xeroderma pigmentosum

A
  • skin damage and increased risk for cancer
  • eyelid scarring
  • corneal ulceration
138
Q

Perseverance structural integrity of epithelial sheet

A

Hemidesmosomes
Cytoskeleton structure
Cell to matrix adhesion

139
Q

Deposit iron in EPI

A

Hudson-stahli line

140
Q

Degeneration of BOWMANS

A

Limbal girdle of Vogt

141
Q

What layer does corneal arcus affect

A

Stroma

142
Q

Warts appear in DESCEMETS

A

Hassall-henle bodies

143
Q

Vertical line in ENDO

A

Krukenberg’s spindle

Ocular Phys (5 decks)

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