Block 9 Flashcards
(143 cards)
1
Q
3 main functions of cornea
A
- refract light
- transmit light
- protect
2
Q
Factors affecting refraction
A
- ant curvature
- ref index from air to TF
- corneal thickness
- post curvature
- ref index from cornea to aqueous
3
Q
Total power of eye
A
60D
4
Q
How much of the power of the eye comes from the cornea
A
40-48D
- 2/3 to 3/4 of power
5
Q
How does the cornea transmit light
A
- little scattering
- little distortion
- max transmission
6
Q
How much scatter is in the cornea
A
<1%
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
8
Q
How sensitive is the cornea
A
One of the most sensitive in the body
9
Q
Innervation of cornea
A
Ophthalmic division of trigeminal nerve
- 60-80 long ciliary n.
10
Q
The cornea is sensitive to
A
- touch
- cold
- chemicals
11
Q
Normal CV of endothelium
A
.25
12
Q
Shape of majority of endothelial cells
A
Hexagonal
13
Q
Does the endothelium regenerate
A
No
14
Q
What happens as you lose endothelial cells
A
Cell density decreases and cells change shape, becoming less hexagonal
15
Q
How much of the cornea is the stroma
A
90%
16
Q
How does cornea maintain transparency
A
Uniform size and spacing of collagen
17
Q
What is the optimal water level in stroma
A
75-80% water
18
Q
Which layer is resistant to deformation, trauma and FB
A
Bowman’s layer
19
Q
Will Bowman’s layer scar?
A
Yes
20
Q
Thickness of bowman’s layer
A
8-14 microns
21
Q
(New) Layer between stroma and descemet’s membrane
A
Dua’s layer
22
Q
How thick is dua’s layer
A
15 microns thick
23
Q
How does the epithelium help maintain a proper hydration
A
Tight junctions
- keep out water
24
Q
How does the stroma help maintain a proper hydration
A
Proteoglycans
- pull water in
25
How does the endothelium help maintain a proper hydration
Leaks fluid into cornea
26
Driving forces of water transport in cornea
Cl- extrusion and Na+ absorption
27
Two ways water moves through cornea
- stroma to endo to aqueous
| - epi to TF
28
Bidirectional water transport channels
Aquaporins
29
What is lost during a minor corneal abrasion
Zonula occludens
30
2 things that happen with a minor abrasion
- edema
| - haziness
31
How does edema affect VA
Decrease VA
32
What happens when there is a more extensive corneal abrasion
Fluid gets into the stroma
33
Fastest healing tissue in the body
Cornea
34
The healing of the cornea relies on
Peptide growth factors
35
How quickly does the cornea heal (minor abrasion)
24-48 hours
36
How quickly can the entire cornea be replaced
2 weeks
37
Which layers of the cornea consume the most oxygen
Endo and epi
38
Which layer of cornea can store glycogen
Epi
39
Compromises the integrity of the epi
Corneal ulcer
40
The epi is impermeable to
Ions
41
Epi and endo are...
Hydrophobic
42
What type of material penetrates the cornea easier
Lipid soluble
43
3 conditions from loss of stability and structure of cornea
- keratoconus
- ectasia
- high/low IOP
44
Corneal thickness at birth
Full thickness
45
Horizontal cornea diameter at birth
90% of full size
| - 10mm
46
Axial length of eye at birth
2/3 of adult size
47
Why are kids typically more hyperopic
Bc the axial length is shorter at birth and must grow
48
At what age does the cornea bc adult size
3 years
49
Sclera is growing until what age
10-12
50
Most eyes are emmetropic by what age
6-8
51
When changes happen in central cornea, affecting transparency
Dec VA
52
Cornea aging changes: sensitivity
Decreased
53
Cornea aging changes: scatter
Increase
54
Cornea aging changes: curvature
Flattens
| - becomes against the rule
55
Cornea aging changes: descemet's thickness
Gets thicker
56
Most common aging change
Corneal arcus
57
White ring formed by cholesterol deposits in peripheral stroma
Corneal arcus
58
Corneal arcus is most common is what pt age range
60-80
59
What is suspected if a pt under 40 has corneal arcus
Hyperlipidemia
60
Corneal arcus: bi or unilateral
Bilateral
61
What layer is affected in corneal arcus
Bowman's
62
What happens to the epi with age
Loss of intracellular junctions causing dec barrier function
63
Horizontal pigmented line at lower lid margin
Hudson-stahli line
64
What age does the hudson-stahli line appear
After 50
65
What causes the Hudson-stahli line
Iron deposits in epi cytoplasm (basal cells)
66
Degeneration of bowman's
Limbal girdle of vogt
67
Yellowish/white opacity at 3 and 9 o'clock
Limbal girdle of vogt
68
What appear in the periphery due to changes in descemet's membrane with age
Hassall-henle bodies
69
Which illumination will you see descemet's warts
Retro
70
Endo cell density with age
Decreases
71
Avg endo cell density in kids
4000 cell/mm^2
72
Avg endo cell density in adults
2500 cell/mm^2
73
How does the cell density change over times (numerically)
Dec .6-1% per year
74
Greater than normal variation in size of endo cells
Polymegathism
75
Increased variability in size and shape of endo
Pleomorphism
76
Vertical line on posterior pole
Krukenberg's spindle
77
Why is there a dec in corneal sensitivity with age
Loss of corneal nerves
78
Refractive error is due to what 2 factors
- axial length
| - corneal curvature
79
Myopic eye length
Longer
80
Hyperopic eye length
Shorter
81
Development of myopia usually occurs around what age
8-14
82
What is myopia caused by
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
Increased outdoor activity does what to your chances of myopia
Reduced risk of myopia
84
Closer to the equator -- more or less myopia
Less myopia
85
Scleral remodeling in myopia
Thinning
86
As the sclera thins, mainly at posterior pole, tissue can bulge out
Ectasia
87
Why can the sclera become yellow with age
Fatty deposits
88
Why does sclera become thin and lose elasticity with age
Degeneration of collagen and elastic fibers
89
3 biomolecules involved in corneal wound healing
- integrins
- cytokines
- growth factors
90
Sense changes in extracellular environment
Corneal integrins
91
Control growth of corneal cells
Cytokines
92
Maintain transparency and induce migration
Growth factors
93
How many cells thick is the epi
5 - 7
94
3 layers of epi
Surface
Wing
Basal
95
How many cells thick is the surface layer of the epi
2
96
How many cells thick is the wing layer of epi
2-3
97
How many cells thick is the basal layer of epi
1
98
Which layer of the corneal epi has cells that divide
Basal
99
How does the epi replace itself
- 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
Time frame for small corneal lesion to heal
24-48 hours
101
If the basement membrane is damaged, how long does it take for corneal to heal
Several months
102
Does the cornea scar
Usually not
103
Corneal epithelium sloughs off bc of poor adhesion (between epi and basement or between basement and underlying tissue)
Recurrent corneal erosion
104
Does bowman's layer regenerate
No
105
Bowman's layer is composed of
Collagen
106
90% of corneal thickness
Stroma
107
Stroma is composed of what 3 things
Collagen, keratocytes, ground substance
108
How long for stroma to reach full strength after wounded
Months
109
How are wounds healed in stroma
- Keratocytes become myofibroblasts
- regenerated collagen is larger and less precisely organized
- myofibroblasts back to keratocytes by apoptosis
110
Descemet's mem healing is regenerated by
Keratocytes and endo
111
Single layer of flat cells
Endo
112
Cells of endo are known as
Polyhedral
- 70-80% hexagonal
- 20-30% heptagonal
113
Would healing of endo
Neighboring cells enlarge, cells remodel, inc number of ion pumps
--> doesn't create new cells
114
Most glucose comes from
Aqueous humor
115
Minor glucose supply
TF and limbal capillaries
116
Glycolysis - 1 glucose gives how much ATP (net)
2
117
Krebs and ETC produce how much ATP
36
118
Which 2 layers will consume oxygen
Endo and epi
119
Where does the epi get oxygen
Limbal vasculature and TF (atmosphere - 155 mmHg)
120
Where does endo get oxygen
Aqueous (40mmHg)
121
Aerobic metabolism deals with which cycle
Krebs
122
Anaerobic metabolism deals with which cycle
Glycolysis and HMP shunt
123
Produces amino acids and intermediates for nucleotide prod (for DNA replication)
HMP shunt
124
Important for the production of components required for rapid regeneration of corneal epithelial cells
HMP shunt
125
In anaerobic conditions, what builds up
Pyruvate, which is converted to lactic acid
126
What does lactate buildup do
Induces epi and stroma edema
127
Situations that can cause too much time in anaerobic conditions
- CLs wearers
| - lots of sleep
128
Painful condition caused by exposure to UV rays (natural or artificial sources)
Photokeratitis or UV Keratitis
129
Low exposure to UV
Inhibited cell mitosis
130
Medium to high exposure to UV
Swollen nuclei and cell death
131
Extreme UV exposure
Complete sloughing of epi cells
132
What also contributes to damage at the higher levels of UV damage
oxygen
133
UV light damage causes what dimers
Thymine (pyramids)
| - cant replicate DNA
134
DNA repair enzyme
UV-specific endonuclease
***exinuclease***
135
Process of DNA repair from UV damage
- Exinucleause cuts DNA on both sides of damage
- remove damage
- gap filled by DNA Pol 1
- DNA ligase complete the bond
136
Deficiency in the excision endonuclease and a reduced ability to repair damage from UV light
Xeroderma pigmentosum
137
Symptoms of xeroderma pigmentosum
- skin damage and increased risk for cancer
- eyelid scarring
- corneal ulceration
138
Perseverance structural integrity of epithelial sheet
Hemidesmosomes
Cytoskeleton structure
Cell to matrix adhesion
139
Deposit iron in EPI
Hudson-stahli line
140
Degeneration of BOWMANS
Limbal girdle of Vogt
141
What layer does corneal arcus affect
Stroma
142
Warts appear in DESCEMETS
Hassall-henle bodies
143
Vertical line in ENDO
Krukenberg's spindle
