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OCULAR PHYSIOLOGY > Cornea 1 > Flashcards

Cornea 1 Flashcards

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

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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.

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4
Q

The cornea has ____ diopters of ____ power.

A

48, plus

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5
Q

The corneas radius of curvature of its outer aspect averages ____mm.

A

7.8mm

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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

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7
Q

T/F The central third of the cornea has a spherical or toroidal (ring/donut shaped) contour.

A

True

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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.

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9
Q

What percentage of incident light above 400nm is transmitted through the cornea?

A

> 99%

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10
Q

Name the 5 layers in the cornea.

A
  1. Epithelium
  2. Bowman’s layer
  3. Stroma
  4. Descemet’s membrane
  5. Endothelium
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11
Q

The cornea transmits radiation from approximately ___nm in the ultraviolet to _____nm in the infrared.

A

310nm, 2500nm

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12
Q

Name the 3 cell types found in the epithelium.

A
  1. Surface cells/Apical cells
  2. Wing cells
  3. Basal cells
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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

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14
Q

The corneal epithelium is a ______, _________, ________ _______ epithelium that is ____ to ______ cells thick.

A

stratified, non-keratinized, non-secretory squamous, 5, 7

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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.

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16
Q

The wing cells of the corneal epithelium is known as the intermediate ____________ stage.

A

differentiation

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17
Q

The basal cells are adhered to the ________ _______.

A

basement membrane

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18
Q

in which corneal epithelial cell layer does mitosis occur?

A

Basal cell layer

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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.

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20
Q

The entire corneal ________ is turned over every ______ days.

A

epithelium, 7

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21
Q

T/F Cell division occurs in all 3 corneal epithelial layers.

A

False, Cell division ONLY occurs in the BASAL layer.

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22
Q

The basal cells originate from _____ _____ in the basal layer of the ______ epithelium.

A

stem cells, limbal

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23
Q

T/F Basal cells have a higher level of metabolic activity and synthetic activity than the more superficial cells.

A

True

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24
Q

The basal cells have more prominent _______, _____ _________ and Golgi apparatus. They also contain significant stores of ______.

A

mitochondria, endoplasmic reticulum, glycogen

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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

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26
Q

The mitotic rate of the corneal epithelium is ___ to ____ per day.

A

10 to 15%

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27
Q

The ____ contains stem cells, which differentiate into ____ cells and migrate onto the ____ of the cornea, constantly ______the supply of basal cells.

A

limbus, basal, center, renewing

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28
Q

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.

A

True

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29
Q

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.

A

irregular, polygonal cellssmall, large, dark, light

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30
Q

In electron microscopy, the smaller, light cells are _____ cells that have recently reached the _____ of the cornea.

A

younger, surface

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31
Q

In electron microscopy, the larger, dark cells are _____ cells that will be _____.

A

mature, sloughed

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32
Q

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.

A

exfoliation holes, corneal surface, hole, superficial

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33
Q

Basal cells adhere to the ______ ______ and stroma via ________.

A

basement membrane, hemidesmosomes

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34
Q

T/F Hemisdesmosomes are linked to anchoring fibrils (pass through Bowman’s Layer into the stroma)

A

True

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35
Q

T/F Desmosomes are integral membrane protein complexes in the basal cell plasma membrane.

A

False Hemidesmosomes not desmosomes

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36
Q

T/F The maintenance of the well organized, stable epithelial structure does not require appropriate cell-substrate and cell to cell adhesion.

A

False. appropriate cell-substrate and cell-cell adhesion is required.

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37
Q

Anchoring fibrils are type ____ collagen and penetrate ___ micrometers into the stroma. The anchoring fibrils end in structures known as ____ ______.

A

VII, 2anchoring plaques

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38
Q

What adhesion complex is destroyed during photorefractive keratectomy surgery and must be reassembled during the healing process (post surgery)?

A

Basal cell adhesions to basement membrane via hemidesmosomes

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39
Q

What junctions are the greatest importance to the epithelial corneal barrier function and where are they found?

A

Zonula Occludens/tight junctions are found ONLY between the superficial cells of the epithelium and completely encircle the cells.

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40
Q

T/F The gap junctions represent an actual anastomosis of the lipid bilayer of the adjoining membranes.

A

False. Tight junctions/zonula occludens not gap junctions

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41
Q

In what layers of the corneal epithelium are gap junctions found?

A

Gap junctions are found in ALL layers and are more numerous in the basal layers than in the superficial cells.

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42
Q

______is pumped from tears to _____, while ______ is transported into the tears. The balanced net flux is ____.

A

Na, stroma,Cl, zero

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43
Q

What eye condition leads to painful recurrent epithelial erosions making the cornea susceptible to edema and infection?

A

Epithelial Basement Membrane Dystrophy (EBMD) caused by abnormal adhesion of the epithelium and a decreased number of hemidesmosomes in the basal cells.

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44
Q

Reduplication of the basement membrane is associated with an ______ incidence of epithelial _____ and occurs in ____ and ____ patients.

A

increased, erosions, aging, diabetic

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45
Q

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.

A

False. reduced depth of penetration

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46
Q

T/F Reduplication of the basement membrane is thickening of basement membrane.

A

True

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47
Q

The basal cells of the epithelium rest on the _____ _____ and is approximately ___ to ___ nm thick.

A

basement membrane, 40, 60

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48
Q

Name the 5 types of tissues found in the epithelial basement membrane.

A
  1. type IV collagen
  2. laminin
  3. proteoglycan perlecan
  4. fibronectin
  5. fibrin
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49
Q

Is the epithelial basement membrane similar in structure and composition to the basal laminas of other squamous epithelia.

A

yes, they have been analyzed histochemically and immunologically.

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50
Q

Basement membrane is also known as ______ _____.

A

Basal Lamina

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51
Q

The primary function of the corneal epithelium is to form a ____ to invasion of the eye by ______ and to _____ excess fluid by the _____.

A

barrier, pathogens, uptake, stroma

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52
Q

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?

A

ceases, retract, thicken, lose, enlarge, migrate, ameboid

to prevent infection

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53
Q

Abrasion of the corneal epithelium demands a ____ healing response to ____ the exposed ____ ____ with cells

A

prompt, recover, basement membrane

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54
Q 
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
A

48 hours

60, 80

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55
Q

After an abrasion and the wound has closed, mitosis ______ to restore the epithelium to its _____ configuration.

A

resumes, normal

56
Q

T/F The corneal epithelial healing process occurs slowly.

A

False. The corneal epithelial healing process occurs rapidly.

57
Q

T/F normal cornea maintians a constant thickness where IOP is below 40 mm Hg

A

F. normal cornea maintians a constant thickness (where IOP is bellow 50mmHg

58
Q

T/F Protein synthesis by epithelial cells decreases during cell migration.

A

False. Increases

59
Q

If there is a IOP higher than 50 mmHg or if there is abnormal endothelial function what happens to the cornea?

A

There is an epithelial edema and increased stromal thickness

60
Q

why does a normal cornea maintain a constant thickness where the IOP is below 50mm Hg?

A

because stromal swelling pressure is in a similar range

61
Q

IP (stromal imbibitions pressure) = IOP - _____?

A

SP (stroma sweeling pressure)

62
Q

Cell migration requires _____.

A

energy

63
Q

Stomal swelling pressure____ with _____ corneal thickness. Therefore mild corneal edema with _____ pressure can lead to ____ imbibition pressure and subsequent epithelial edema and Bullae.

A

decreases, increased.

elevated, high.

64
Q

During stromal wound healing, restoring tensile strength involves what three things?

A

Resynthesis and cross linking of collagen,
alterations in proteoglycan synthesis,
gradual wound remodeling

65
Q

What are bullae?

A

Bullae are large blisters on the skin that are filled with clear fluid

66
Q

What is imbibition ?

A

Imbibition is defined as the displacement of one fluid by another immiscible fluid.

67
Q

During stromal wound healing within hours _________ cells appear around areas of cellular neccrosis in a penetrating corneal wound, followed thereafter by _______

A

polymorphonuclea, monocytes

68
Q

Corneal epithelial cells are dependent on _____ ______ and glycolytic activity _______ during cell migration.

A

anaerobic glycolysis, increases

69
Q

Tensil strenth increases gradually up to the ____ post-op year.

A

4th

70
Q

T/F: Incisions in avascular cornea far from the limbus heal quickly than peripheral corneal wounds

A

F. incisions in avascualr cornea far from the limbus heal slowly than peripheral corneal wounds.

71
Q

Why do wounds in the limbus heal quickly ?

A

becuase it has a greater blood supply

72
Q

T/F: Use of potent topical steroid may delay the early phases of corneal wound healing.

A

T

73
Q

T/F One of the earliest changes observed during the healing process is a decrease in the glycogen levels in the migrating cells.

A

True

74
Q

Incisions in avascular cornea far form the limbus heal more slowly than peripheral cornea wounds or in chronically inflamed corneas with _____________

A

neovascularization

75
Q

Which membrane is the basement membrane on which the corneal endothelium rests?

A

Descement’s

76
Q

How thick is Descemet’s Membrane?

A

10-15v microns thick

77
Q

_______ and _______ produce and maintain the ECM.

A

Keatocytes, fibroblasts (not to be confused with keratinocytes of the skin)

78
Q

What three things are descemet;s membrane composed of?

A

type IV collagen, laminin, fibronectin

79
Q

What type of enzyme is descemet’s membrane highly resistant to?

A

proteolytic enzymes

80
Q

The collagen fibers have a refractive index of _____ compared with the extrafibrillar matrix’s refractive index of _____.

A

1.411, 1.365 Despite this disparity, minimal light scattering occurs because of the highly uniform size and spacing of the collagen fibers.

81
Q

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.

A

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
Q

Compared to the cornea, in the scleraFibers are _____ with greatly ______ diameters and are not______ or ______ ______.

A

large, varying,

orderly, closely spaced

83
Q

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.

A

increased, 2, increase, 4, 24, 2

84
Q

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 ___ __________.

A

delayed, not established

85
Q

When are descementocele formed?

A

After destruction of the epithelium and stroma

86
Q

Descementocele is what?

A

A hernia of Descemet’s membrane.

87
Q

With damage to epithelial or endothelial barrier, the cornea swells. How does this effect the cornea?

A

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
Q

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.

A

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
Q

T/F Growth factors and other signaling molecules are being studied for potential in promoting corneal healing,

A

True

90
Q

What type of descemet’s membrane is secreted in Fuch’s dystrophy?

A

an abnormal descemet’s membrane

91
Q

After wound healing, the adhesion of the epithelium is ________ by formation of new ________ in the basal cell layer.

A

reestablished, hemidesmosomes

92
Q

T/F Fuch’s dystrophy is a disease of the epithelial cells

A

F Endothelial cells

93
Q

what happens in the progression of Fuch’s dystrophy?

A

endothelial cell function is decreased, cells are lost, and the cornea decompensates( loss of physiological compensation)

94
Q

Waterlike excrescenses of colalgenous material known as _______ form on the _______ surface of the descemet’s membrane.

A

Guttata, posterior

95
Q

What does guttata cuase the endothelial cells to do?

A

thin and englarge

96
Q

T/F Guttata apear like dark spots in pictures

A

True

97
Q

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.

A

False. , a normal epithelium with adhesion complexes is formed soon after healing.

98
Q

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.

A

basement membrane, delayed, 12

99
Q

In the corneal endothelium Newborn cells density is greater______cells/mm^2Adult cells denstiy _____-______ cells/mm^2minimum cell density ____-______ cells/mm^2

A

5500
3000-2500
4000-700

100
Q

the endothelium layer of the cornea is a ______ layer of ______ cells covering posterior surface of the cornea

A

single, polygonal

101
Q

With age the endothelial cells density _______ in the endothelium of the cornea

A

decreases

102
Q 
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
A

20

4to 6

103
Q

Bowman’s layer, which among mammals is found only in _______, lies ______ the basement membrane and is approximately ____ µm thick.

A

primates, beneath, 12

104
Q

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

A

0.6, central endothelial100

105
Q

Bowman’s layer is ______ and is made up of randomly arranged _____ ______.

A

acellular, collagen fibrils

106
Q

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.

A

True

107
Q

T/F Bowman’s layer can also be considered a modified superficial layer of Descemets membrane.

A

False. Bowman’s layer can also be considered a modified superficial layer of the stroma

108
Q

_______ and _______ produce and maintain the ECM.

A

Keatocytes, fibroblasts

109
Q

Active endothlium cells are metabolically active in ______, __________ and _________

A

transport, synthesis, and secretory functions

110
Q

In a typical active endothelium cells there will be what 4 things?

A

large nucleusnumerous mitochondriaprominent endoplasmic reticulumgolgi apparatus

111
Q

it has been shown that there is a significant correlation of histologic _______ endothelial cells counts with _________ microscopic high power field cell density

A

corneal, specular

112
Q

What is the correlation in endothelial mophometry between density and age and number of cells per high power field vs age?

A

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
Q

Corneal endothelial cells are interconnected by what two juncitons?

A

tight and gap juncitons

114
Q

T/F tight juncitonal complexes are zonula occludens rather than macula occludens in that they completely encircle the cells

A

F tight juncitonal complexes are macula occludens rather than zonlua occludens in that they do not completetly encirlce the cells

115
Q

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.

A

200, 250
bundles
2.0
9, 260

116
Q

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

A

predominantly, lamellar, parallel, separated

117
Q

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.

A 
limbus
circumferentially 
1.5, 2.0
 30, 
42, 44
118
Q

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.

A

True

119
Q

T/F the corneal endothelium forms a leaky barrier between the aqueous humor and the stroma

A

T. Although it impeds the free flow of water and solutes ,

120
Q

Gap junctions are ______ and are observed primarily on the ______ membranes of the corneal endothelial cells

A

numerous, lateral

121
Q

What other membrane are gap juncitons present in besides the lateral?

A

apicolateral membranes

122
Q

T/F Gap junctions do not contribute to the endothelial barrier, but they function in intercellular communication

A

T

123
Q

The collagen fibers have a refractive index of _____ compared with the extrafibrillar matrix’s refractive index of _____.

A

1.411, 1.365

124
Q

The collagen fibers in the stroma are primarily made of what types of collagen?

A

primarily made of type I collagen, with lesser amounts of types V and VI.

125
Q

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.

A

True

126
Q

Compared to the cornea, in the SCLERA:Fibers are _____ with greatly ______ diameters and are ___ ______ or ______ ______.Not orderly or closely spaced

A

large, varying,Not orderly, closely spaced

127
Q

What is a reason that the sclera has a great deal of light scatter and is non-transparent?

A

Fibers in the sclera are large with greatly varying diameters and are not orderly or closely spaced.

128
Q

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.

A

vary, small, diameter, weak, small

129
Q

In the cornea to maintain transparency, it is _____ that the distance between the collagen fibrils be ____ than _____ ______ the wavelength of visible light.

A

required, less, one half

130
Q

With damage to epithelial or endothelial barrier, the cornea swells. How does this effect the cornea?

A

It will lead to a loss of corneal transparency

131
Q

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.

A

greater, lower,

132
Q

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.

A

evaporates, 2.5 µL/cm2/hr, 5%,daynightime

133
Q

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.

A

False, worse in the morning

134
Q

Localized areas of corneal drying and evaporation may result in focal corneal ______, known as _____.

A

drying, dellen

135
Q

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..

A

True

OCULAR PHYSIOLOGY (13 decks)

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