Cornea 1 Flashcards
(134 cards)
1
Q
The cornea is ______ shaped and is ____mm horizontally and ____mm vertically.
A) 12.6mm 11.7 mm
B) 11.6 mm 12 mm
C) 12.6 mm 12mm
D) 11.6 mm 11.7mm
A
oval, 12.6mm, 11.7mm
3
Q
T/F The posterior surface is the major refractive component of the eye.
A
False. The anterior surface is the major refractive component of the eye.
4
Q
The cornea has ____ diopters of ____ power.
A
48, plus
5
Q
The corneas radius of curvature of its outer aspect averages ____mm.
A
7.8mm
6
Q
What is the thickness of the central cornea in mm?What is the thickness of the peripheral cornea in mm? A) 0.72 mm 0.82mm B) 0.52mm 0.62 mm C) 0.52 mm 0.82mm D) 0.62mm 0.52mm
A
B)0.52 mm central cornea
0.62 mm peripheral cornea
7
Q
T/F The central third of the cornea has a spherical or toroidal (ring/donut shaped) contour.
A
True
8
Q
T/F The peripheral portion of the cornea is thinner than the central portion.
A
False, the peripheral portion is thicker than the central portion.
9
Q
What percentage of incident light above 400nm is transmitted through the cornea?
A
> 99%
10
Q
Name the 5 layers in the cornea.
A
- Epithelium
- Bowman’s layer
- Stroma
- Descemet’s membrane
- Endothelium
11
Q
The cornea transmits radiation from approximately ___nm in the ultraviolet to _____nm in the infrared.
A
310nm, 2500nm
12
Q
Name the 3 cell types found in the epithelium.
A
- Surface cells/Apical cells
- Wing cells
- Basal cells
13
Q
How many cells thick is the surface/apical layer of the corneal epithelium?How many cells thick is the wing cell layer of the corneal epithelium?How many cells thick is the basal cell layer of the corneal epithelium?
A
3-4 cells thick surface/apical layer
1-3 cells thick wing layer
1 cell thick basal layer
14
Q
The corneal epithelium is a ______, _________, ________ _______ epithelium that is ____ to ______ cells thick.
A
stratified, non-keratinized, non-secretory squamous, 5, 7
15
Q
T/F Basal cells are differentiated squamous cells that are sloughed from the corneal surface.
A
False. Surface/apical cells are the outermost corneal epithelial cells that are differentiated squamous cells that are sloughed at the surface.
16
Q
The wing cells of the corneal epithelium is known as the intermediate ____________ stage.
A
differentiation
17
Q
The basal cells are adhered to the ________ _______.
A
basement membrane
18
Q
in which corneal epithelial cell layer does mitosis occur?
A
Basal cell layer
19
Q
T/F As the cell division occurs, the basal daughter cells move toward the surface of the cornea and begin to differentiate, forming one to three layers of the surface/apical cell.
A
False. The basal daughter cells move towards the surface, differentiate and become Wing cells.
20
Q
The entire corneal ________ is turned over every ______ days.
A
epithelium, 7
21
Q
T/F Cell division occurs in all 3 corneal epithelial layers.
A
False, Cell division ONLY occurs in the BASAL layer.
22
Q
The basal cells originate from _____ _____ in the basal layer of the ______ epithelium.
A
stem cells, limbal
23
Q
T/F Basal cells have a higher level of metabolic activity and synthetic activity than the more superficial cells.
A
True
24
Q
The basal cells have more prominent _______, _____ _________ and Golgi apparatus. They also contain significant stores of ______.
A
mitochondria, endoplasmic reticulum, glycogen
25
Q
The corneal epithelium is maintained by a ______ cycle of shedding of _______ cells and proliferation of cells in the _____ layer.
A
constant, superficial, basal
26
The mitotic rate of the corneal epithelium is ___ to ____ per day.
10 to 15%
27
The ____ contains stem cells, which differentiate into ____ cells and migrate onto the ____ of the cornea, constantly ______the supply of basal cells.
limbus, basal, center, renewing
28
T/F The corneal epithelium is maintained by a balance among sloughing of cells from the corneal surface, cell division in the basal layer, and centripetal migration of cells from the limbus.
True
29
When examined with scanning electron microscopy the surface of the cornea is seen as an _____ array of ______ cells. These cells can be divided into populations of ____ and _____ cells or _____ and ______ cells.
irregular, polygonal cellssmall, large, dark, light
30
In electron microscopy, the smaller, light cells are _____ cells that have recently reached the _____ of the cornea.
younger, surface
31
In electron microscopy, the larger, dark cells are _____ cells that will be _____.
mature, sloughed
32
In electron microscopy, breaks in the epithelium, known as ______ ______ are present. These represent areas where a cell is in the process of peeling off the ______ ______, forming a ___ through which the underlying _____ cell can be seen.
exfoliation holes, corneal surface, hole, superficial
33
Basal cells adhere to the ______ ______ and stroma via ________.
basement membrane, hemidesmosomes
34
T/F Hemisdesmosomes are linked to anchoring fibrils (pass through Bowman's Layer into the stroma)
True
35
T/F Desmosomes are integral membrane protein complexes in the basal cell plasma membrane.
False Hemidesmosomes not desmosomes
36
T/F The maintenance of the well organized, stable epithelial structure does not require appropriate cell-substrate and cell to cell adhesion.
False. appropriate cell-substrate and cell-cell adhesion is required.
37
Anchoring fibrils are type ____ collagen and penetrate ___ micrometers into the stroma. The anchoring fibrils end in structures known as ____ ______.
VII, 2anchoring plaques
38
What adhesion complex is destroyed during photorefractive keratectomy surgery and must be reassembled during the healing process (post surgery)?
Basal cell adhesions to basement membrane via hemidesmosomes
39
What junctions are the greatest importance to the epithelial corneal barrier function and where are they found?
Zonula Occludens/tight junctions are found ONLY between the superficial cells of the epithelium and completely encircle the cells.
40
T/F The gap junctions represent an actual anastomosis of the lipid bilayer of the adjoining membranes.
False. Tight junctions/zonula occludens not gap junctions
41
In what layers of the corneal epithelium are gap junctions found?
Gap junctions are found in ALL layers and are more numerous in the basal layers than in the superficial cells.
42
______is pumped from tears to _____, while ______ is transported into the tears. The balanced net flux is ____.
Na, stroma,Cl, zero
43
What eye condition leads to painful recurrent epithelial erosions making the cornea susceptible to edema and infection?
Epithelial Basement Membrane Dystrophy (EBMD) caused by abnormal adhesion of the epithelium and a decreased number of hemidesmosomes in the basal cells.
44
Reduplication of the basement membrane is associated with an ______ incidence of epithelial _____ and occurs in ____ and ____ patients.
increased, erosions, aging, diabetic
45
T/F The abnormality of epithelial adhesion may be a result of a increased depth of penetration of anchoring fibrils through thickened basement membrane into the stroma.
False. reduced depth of penetration
46
T/F Reduplication of the basement membrane is thickening of basement membrane.
True
47
The basal cells of the epithelium rest on the _____ _____ and is approximately ___ to ___ nm thick.
basement membrane, 40, 60
48
Name the 5 types of tissues found in the epithelial basement membrane.
1. type IV collagen
2. laminin
3. proteoglycan perlecan
4. fibronectin
5. fibrin
49
Is the epithelial basement membrane similar in structure and composition to the basal laminas of other squamous epithelia.
yes, they have been analyzed histochemically and immunologically.
50
Basement membrane is also known as ______ _____.
Basal Lamina
51
The primary function of the corneal epithelium is to form a ____ to invasion of the eye by ______ and to _____ excess fluid by the _____.
barrier, pathogens, uptake, stroma
52
After abrasion, mitosis ____ and the cells at the wound edge ____, ____ and ___ their hemidesmosomal attachments to the basement membrane. The cells ____ and the epithelial sheet begins to ____ by _____ movement to cover the defect.
Why is this done?
ceases, retract, thicken, lose, enlarge, migrate, ameboid
to prevent infection
53
Abrasion of the corneal epithelium demands a ____ healing response to ____ the exposed ____ ____ with cells
prompt, recover, basement membrane
54
```
A 6mm diameter epithelial wound is closed within ___ hours, the rate is ___to ___ micrometer/hr.
a) 24 hrs 50-80
b) 24 hrs 60-80
C) 48 hrs 50-80
D) 48 hrs 60-80
```
48 hours
| 60, 80
55
After an abrasion and the wound has closed, mitosis ______ to restore the epithelium to its _____ configuration.
resumes, normal
56
T/F The corneal epithelial healing process occurs slowly.
False. The corneal epithelial healing process occurs rapidly.
57
T/F normal cornea maintians a constant thickness where IOP is below 40 mm Hg
F. normal cornea maintians a constant thickness (where IOP is bellow 50mmHg
58
T/F Protein synthesis by epithelial cells decreases during cell migration.
False. Increases
59
If there is a IOP higher than 50 mmHg or if there is abnormal endothelial function what happens to the cornea?
There is an epithelial edema and increased stromal thickness
60
why does a normal cornea maintain a constant thickness where the IOP is below 50mm Hg?
because stromal swelling pressure is in a similar range
61
IP (stromal imbibitions pressure) = IOP - _____?
SP (stroma sweeling pressure)
62
Cell migration requires _____.
energy
63
Stomal swelling pressure____ with _____ corneal thickness. Therefore mild corneal edema with _____ pressure can lead to ____ imbibition pressure and subsequent epithelial edema and Bullae.
decreases, increased.
| elevated, high.
64
During stromal wound healing, restoring tensile strength involves what three things?
Resynthesis and cross linking of collagen,
alterations in proteoglycan synthesis,
gradual wound remodeling
65
What are bullae?
Bullae are large blisters on the skin that are filled with clear fluid
66
What is imbibition ?
Imbibition is defined as the displacement of one fluid by another immiscible fluid.
67
During stromal wound healing within hours _________ cells appear around areas of cellular neccrosis in a penetrating corneal wound, followed thereafter by _______
polymorphonuclea, monocytes
68
Corneal epithelial cells are dependent on _____ ______ and glycolytic activity _______ during cell migration.
anaerobic glycolysis, increases
69
Tensil strenth increases gradually up to the ____ post-op year.
4th
70
T/F: Incisions in avascular cornea far from the limbus heal quickly than peripheral corneal wounds
F. incisions in avascualr cornea far from the limbus heal slowly than peripheral corneal wounds.
71
Why do wounds in the limbus heal quickly ?
becuase it has a greater blood supply
72
T/F: Use of potent topical steroid may delay the early phases of corneal wound healing.
T
73
T/F One of the earliest changes observed during the healing process is a decrease in the glycogen levels in the migrating cells.
True
74
Incisions in avascular cornea far form the limbus heal more slowly than peripheral cornea wounds or in chronically inflamed corneas with _____________
neovascularization
75
Which membrane is the basement membrane on which the corneal endothelium rests?
Descement's
76
How thick is Descemet's Membrane?
10-15v microns thick
77
_______ and _______ produce and maintain the ECM.
Keatocytes, fibroblasts (not to be confused with keratinocytes of the skin)
78
What three things are descemet;s membrane composed of?
type IV collagen, laminin, fibronectin
79
What type of enzyme is descemet's membrane highly resistant to?
proteolytic enzymes
80
The collagen fibers have a refractive index of _____ compared with the extrafibrillar matrix’s refractive index of _____.
1.411, 1.365 Despite this disparity, minimal light scattering occurs because of the highly uniform size and spacing of the collagen fibers.
81
T/F Maurice proposed that corneal transparency is not a consequence of a crystalline lattice arrangement of collagen fibrils within stromal lamellas and that light scattered by individual fibrils of uniform diameter is canceled by destructive interference with scattered light from adjacent fibers; therefore light is scattered only in the backward direction.
False. corneal transparency IS a consequence of a crystalline lattice arrangement of collagen fibrils within stromal lamellas therefore light is scattered only in the FORWARD direction
82
Compared to the cornea, in the scleraFibers are _____ with greatly ______ diameters and are not______ or ______ ______.
large, varying,
| orderly, closely spaced
83
Following wounding of rat corneas, _______ expression of glucose transporter GLUT1mRNA is detectable by ___ hours after wounding, and GLUT1 protein levels ____ by ___ hours, peaking at ___ hours after wounding and remaining elevated for at least ____ weeks.
increased, 2, increase, 4, 24, 2
84
In conditions such as basement membrane dystrophy, diabetes, persistent or recurrent epithelial defects and severe injuries(alkali burns) healing is _______ or normal epithelial adhesion is ___ __________.
delayed, not established
85
When are descementocele formed?
After destruction of the epithelium and stroma
86
Descementocele is what?
A hernia of Descemet's membrane.
87
With damage to epithelial or endothelial barrier, the cornea swells. How does this effect the cornea?
It will lead to a loss of corneal transparencyThe uptake of water causes formation of “lakes” devoid of collagen fibers within the stroma. This causes increased divergence of refractive index within the stroma, as well as an increase in distance between collagen fibrils, leading to a wavelength-dependent loss of light transmittance that increases with the amount of corneal swelling.
88
The fibril diameter is ______ in the anterior cornea than in the posterior cornea, and the density of fibrils is _____ in the anterior cornea than in the posterior cornea.
greater, lowerThis leads to a twofold (in humans) and threefold (in rabbits) increase in light scatter by the anterior cornea as compared with the posterior cornea.
89
T/F Growth factors and other signaling molecules are being studied for potential in promoting corneal healing,
True
90
What type of descemet's membrane is secreted in Fuch's dystrophy?
an abnormal descemet's membrane
91
After wound healing, the adhesion of the epithelium is ________ by formation of new ________ in the basal cell layer.
reestablished, hemidesmosomes
92
T/F Fuch's dystrophy is a disease of the epithelial cells
F Endothelial cells
93
what happens in the progression of Fuch's dystrophy?
endothelial cell function is decreased, cells are lost, and the cornea decompensates( loss of physiological compensation)
94
Waterlike excrescenses of colalgenous material known as _______ form on the _______ surface of the descemet's membrane.
Guttata, posterior
95
What does guttata cuase the endothelial cells to do?
thin and englarge
96
T/F Guttata apear like dark spots in pictures
True
97
T/F When a corneal abrasion is limited to the epithelium and the basement membrane is not damaged, a normal epithelium with adhesion complexes is not formed after healing.
False. , a normal epithelium with adhesion complexes is formed soon after healing.
98
In experimental keratectomy wounds of the cornea in which basement membrane is removed, the epithelium must lay down new ______ ______ after healing and development of normal adhesion complexes is _____ for more than ____ months.
basement membrane, delayed, 12
99
In the corneal endothelium Newborn cells density is greater______cells/mm^2Adult cells denstiy _____-______ cells/mm^2minimum cell density ____-______ cells/mm^2
5500
3000-2500
4000-700
100
the endothelium layer of the cornea is a ______ layer of ______ cells covering posterior surface of the cornea
single, polygonal
101
With age the endothelial cells density _______ in the endothelium of the cornea
decreases
102
```
Endothelial cells are approxiamatly ____ microns in diamter and __to___ microns thick
A)20 , 5-6
B)30, 4-6
C)20, 4-6
D) 20 -4-7
```
20
| 4to 6
103
Bowman’s layer, which among mammals is found only in _______, lies ______ the basement membrane and is approximately ____ µm thick.
primates, beneath, 12
104
In a typical patient with no histroy of coneal disease or surgery (Borne, Neison, and Hodge reported a ____% decrease in ____ _____ cell density per yearThis indicates that adequat cells are available for a lifetime of well over _____ years
0.6, central endothelial100
105
Bowman's layer is ______ and is made up of randomly arranged _____ ______.
acellular, collagen fibrils
106
T/F Bowman's layer appears to be structureless by light microscopy, but under the electron microscope it revealed to be made if randomly arranged collage fibrils.
True
107
T/F Bowman's layer can also be considered a modified superficial layer of Descemets membrane.
False. Bowman's layer can also be considered a modified superficial layer of the stroma
108
_______ and _______ produce and maintain the ECM.
Keatocytes, fibroblasts
109
Active endothlium cells are metabolically active in ______, __________ and _________
transport, synthesis, and secretory functions
110
In a typical active endothelium cells there will be what 4 things?
large nucleusnumerous mitochondriaprominent endoplasmic reticulumgolgi apparatus
111
it has been shown that there is a significant correlation of histologic _______ endothelial cells counts with _________ microscopic high power field cell density
corneal, specular
112
What is the correlation in endothelial mophometry between density and age and number of cells per high power field vs age?
There is a decrease in density of corneal endothelial cells with increase in age There is a decrease in number of cells per high-power field with increase in age
113
Corneal endothelial cells are interconnected by what two juncitons?
tight and gap juncitons
114
T/F tight juncitonal complexes are zonula occludens rather than macula occludens in that they completely encircle the cells
F tight juncitonal complexes are macula occludens rather than zonlua occludens in that they do not completetly encirlce the cells
115
The stroma is made up of ____ to ____ lamellas of collagen fibers.
The lamellas are formed by ____ of collagen fibers approximately ___ µm thick and ___ to ____ µm wide.
200, 250
bundles
2.0
9, 260
116
The stroma is__________ an ECM comprised of a ______ arrangement of collagen fibrils running _____ to the corneal surface, with the individual collagen fibrils are ______ by a matrix of proteoglycans
predominantly, lamellar, parallel, separated
117
At the ____, the collagen fibers turn and run ________ forming an annulus ___ to ___ mm wide around the cornea. The fibers are approximately ____ nm in diameter and are spaced about ___ to ___ nm apart.
```
limbus
circumferentially
1.5, 2.0
30,
42, 44
```
118
T/F The collagen fibers of the stroma stretch from limbus to limbus, lying obliquely to one another in the anterior stroma and orthogonally in the posterior stroma.
True
119
T/F the corneal endothelium forms a leaky barrier between the aqueous humor and the stroma
T. Although it impeds the free flow of water and solutes ,
120
Gap junctions are ______ and are observed primarily on the ______ membranes of the corneal endothelial cells
numerous, lateral
121
What other membrane are gap juncitons present in besides the lateral?
apicolateral membranes
122
T/F Gap junctions do not contribute to the endothelial barrier, but they function in intercellular communication
T
123
The collagen fibers have a refractive index of _____ compared with the extrafibrillar matrix’s refractive index of _____.
1.411, 1.365
124
The collagen fibers in the stroma are primarily made of what types of collagen?
primarily made of type I collagen, with lesser amounts of types V and VI.
125
T/F Maurice proposed that corneal transparency is a consequence of a crystalline lattice arrangement of collagen fibrils within stromal lamellas and that light scattered by individual fibrils of uniform diameter is canceled by destructive interference with scattered light from adjacent fibers; therefore light is scattered only in the forward direction.
True
126
Compared to the cornea, in the SCLERA:Fibers are _____ with greatly ______ diameters and are ___ ______ or ______ ______.Not orderly or closely spaced
large, varying,Not orderly, closely spaced
127
What is a reason that the sclera has a great deal of light scatter and is non-transparent?
Fibers in the sclera are large with greatly varying diameters and are not orderly or closely spaced.
128
The sizes of collagen fibers in the cornea ____, abeit within a relatively _____ range. Although the collagen fibers vary in _____, they remain ____ scatterers of light because their diameter is a ____ fraction of the wavelengths of visible light.
vary, small, diameter, weak, small
129
In the cornea to maintain transparency, it is _____ that the distance between the collagen fibrils be ____ than _____ ______ the wavelength of visible light.
required, less, one half
130
With damage to epithelial or endothelial barrier, the cornea swells. How does this effect the cornea?
It will lead to a loss of corneal transparency
131
The fibril diameter is ______ in the anterior cornea than in the posterior cornea, and the density of fibrils is _____ in the anterior cornea than in the posterior cornea.
greater, lower,
132
Water _______ from the corneal surface at a rate of ______. Evaporation accounts for a ___ thinning of the cornea during the ____, compared with the corneal thickness measured when the eyelids open in the morning after ______ closure.
evaporates, 2.5 µL/cm2/hr, 5%,daynightime
133
T/F In patients with comprised endothelial metabolic pump function, such as in Fuch’s endothelial dystrophy, epithelial edema is better in the morning when arising as a result of lack of evaporation at night when the lids are close.
False, worse in the morning
134
Localized areas of corneal drying and evaporation may result in focal corneal ______, known as _____.
drying, dellen
135
T/F The persistence of dellen may reflect the decrease in stromal fluid flow facility when stromal hydration is abnormal in addition to minimal lateral flow of water in the cornea..
True
