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Anatomy and Biochemisty > Exam 1 Remington- Cornea > Flashcards

Exam 1 Remington- Cornea Flashcards

1
Q

What are the two functions of the cornea?

A

Transmission and Refraction

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2
Q

What is refraction of the cornea dependent on?

A

Curvatures, length, different indices

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3
Q

Anterior diameter of the cornea

A

12 mm horizontal, 11 mm vertical

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4
Q

Posterior diameter of the cornea

A

Horizontal and vertical diameters of 11.7 mm, sclera impinges inferiorly into cornea

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5
Q

Central thickness of the cornea

A

0.53 mm

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6
Q

Peripheral thickness of the cornea

A

0.71 mm

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7
Q

Anterior radius of curvature of the cornea

A

7.8 mm

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8
Q

Posterior radius of curvature of the cornea

A

6.5 mm

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9
Q

_____ radius of curvature means a steeper curve

A

Shorter

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10
Q

What is regular astigmatism?

A

Principle meridians 90 degrees apart

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11
Q

What are 3 types of regular astigmatism?

A

WTR, ATR, and oblique

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12
Q

What is WTR astigmatism?

A

Vertical meridian is steepest (shortest radius of curvature) think football

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13
Q

What is ATR astigmatism?

A

Horizontal meridian is steepest

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14
Q

What is oblique astigmatism?

A

Steepest meridian at 45 or 135 degrees

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15
Q

What is irregular astigmatism?

A

Principle meridians are not 90 degrees apart

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16
Q

How is irregular astigmatism corrected?

A

Contact lenses

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17
Q

What is the function of the plasma membrane lipid bilayer?

A

Controls molecular entrance and exit

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18
Q

What is the function of the cytoskeleton?

A

Structure and intercellular transport

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19
Q

What is the function of ribosomes?

A

Manufactures protein

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20
Q

What is the function of the endoplasmic reticulum?

A

Protein/lipid synthesis

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21
Q

What is the function of the Golgi apparatus?

A

Package proteins

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22
Q

3 types of cellular transport

A

Diffusion, facilitated diffusion, active transport

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23
Q

What do aquaporins do?

A

Move water

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24
Q

What type of channels are aquaporins?

A

Bidirectional in the cornea and lens

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25
Q

3 types of cell surfaces

A

Apical, lateral, and basal

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26
Q

What is a basal cell surface?

A

Sits on basement membrane, connective tissue

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27
Q

The basement membrane consists of what 2 types of lamina?

A

Basal and reticular

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28
Q

Basal lamina is secreted by what cell?

A

Epithelial

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29
Q

Reticular lamina secreted by what cell?

A

CT layer

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30
Q

What are the 2 shapes of intercellular junctions?

A

Zonular and macular

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31
Q

Zonular

A

Belt-like goes all the way around cell

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32
Q

Macular

A

Spot-like

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33
Q

What are the 2 types of intercellular junctions?

A

Adhering and occluding

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34
Q

Adhering intercellular junction

A

Narrow intercellular space, transmembrane adhesion molecules, and contributes to cell stability

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35
Q

Occluding intercellular junction

A

Focal fusion of outer leaflet of plasma membranes, seals off intercellular space (NOTHING gets through)

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36
Q

What is a terminal bar?

A

Adjacent ZO + ZA

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37
Q

Desmosomes

A

Circular attachment plaque, filaments extend into cellular cytoplasm, adhesive mucoprotein fills intercellular space

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38
Q

Hemidesmosomes

A

Attachment of basal surface to underlying CT, filaments join intercellular plaque to plaque in CT

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39
Q

Gap junctions

A

Kind of tube, sends from one cell to the next rapidly

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40
Q

Connexon

A

Transmembrane channel or pore

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41
Q

What does a connexon do?

A

Joins cytoplasm of adjoining cells

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42
Q

A connex___ is composed of 6 protein connex___

A

-on, -in

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43
Q

What do gap junctions do?

A

Permits passage of small molecules, nutrients, and ions

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44
Q

Glycocalyx

A

Gycoprotein covering surface of the cell

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45
Q

The corneal epithelium consists of what kind of cells?

A

Stratified squamous

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46
Q

What does the surface layer of the corneal epithelium consist of?

A

Non-keratinized, microvilli, glycocalyx, intercellular junctions (desmosomes and zonular occludens)

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47
Q

What is the function of zonular occludens in the intercellular junctions?

A

Semi-permeable membrane

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48
Q

What is the purpose of fluorescein straining in evaluating the corneal epithelial surface?

A

Evaluates the barrier function of the surface layer

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49
Q

What happens when fluorescein is instilled in the tear film?

A

Flurescein will not penetrate the epithelial tissue as long as ZO are intact. If disrupted, dye can pass through Bowman’s layer into the anterior stroma.

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50
Q

What is in the wing cell layer of the corneal epithelium?

A

Intercellular junctions ( desmosomes and gap junctions), DOES NOT contain ZO

51
Q

What is known as the transition layer of the corneal epithelium?

A

Wing cell layer

52
Q

What is known as the germinative layer of the corneal epithelium?

A

Basal layer

53
Q

What intercellular junctions are in the basal layer of the corneal epithelium?

A

Desmosomes, gap junctions, hemidesmosomes

54
Q

What secretes the basal lamina portion of the BM?

A

Basal layer

55
Q

In hemidesmosomes, fibrils attach to _____ in stroma

A

Plaques

56
Q

What do plaques contain?

A

Laminin

57
Q

What are two causes of recurrent corneal erosion?

A

EBMD ( epithelial basement membrane dystrophy) and incomplete healing of abrasion

58
Q

Dystrophy

A

Condition caused by defective nutrition or metabolism, also malformed hemidesmosomes

59
Q

What are signs and symptoms of recurrent corneal erosion?

A

Areas of sloughed epi, pain

60
Q

What is the treatment of recurrent corneal erosion?

A

Bandage contact lens and corneal puncture

61
Q

What does corneal puncture do?

A

Stimulates BM adhesion

62
Q

Epithelial replacement is _______

A

Constant

63
Q

Where does cell division occur in the corneal epithelium?

A

Basal layer

64
Q

The basal cells in the corneal epithelium is replenished from what?

A

Stem cells in the limbus

65
Q

How do cells move in epithelial replacement?

A

Basal layer to wing cell layer to surface, barrier function maintained

66
Q

Where are surface cells sloughed?

A

Into tear film

67
Q

What is the cellular composition of Bowman’s layer?

A

Dense irregular CT, acellular

68
Q

Bowman’s layer is considered a ______ layer

A

Transition

69
Q

How is Bowman’s layer compared to the stroma?

A

Smaller and less regular fibers than stroma

70
Q

Bowman’s layer is produced _____ and cannot be _______

A

Prenatally, regenerated

71
Q

What is a pterygium?

A

Conj invades corneal tissue, Bowman’s layer is lysed

72
Q

What is another name for stroma?

A

Substantia propria

73
Q

What is the cellular composition of stroma?

A

Regular dense CT, collagen fibrils, fibroblasts, ground substance

74
Q

What is lamellae?

A

Bundles of collagen

75
Q

What is the orientation of lamellae?

A

Fibers are parallel to surface

76
Q

What is the extent of fibers for the lamellae?

A

Fibers extend from limbus to limbus

77
Q

The _____ stroma has a higher incidence of cross liniing among collagen fibers than ______. Why?

A

Anterior, posterior. Creates more rigidity helping to maintain corneal curvature

78
Q

What are two names (same cell) for the cells in stroma?

A

Fibroblasts= keratocytes

79
Q

What junctions are fibroblasts joined by in the stroma?

A

Gap junctions (can get between cells quickly)

80
Q

What is ground substance composed of?

A

Proteoglycans and glycosaminoglycans (GAGs)

81
Q

What do proteoglycans so?

A

Increase tensile strength

82
Q

What are GAGs?

A

Negatively charged side chains

83
Q

Are GAGs hydrophilic or hydrophobic?

A

Hydrophilic

84
Q

What do GAGs do?

A

Maintain component spacing

85
Q

What is the theory of transparency?

A

Light should pass straight through the cornea, scattered light causes glare

86
Q

How are fibers arranged in the theory of transparency?

A

Fibers arranged in a regular lattice pattern

87
Q

_____ interference occurs in the theory of transparency

A

Destructive

88
Q

What is reduced in the theory of transparency due to destructive interference?

A

Light scattering is reduced, as long as the distance between different refractive indices is less than 1/2 wavelength of light

89
Q

What is the relationship between destructive interference and light scatter?

A

Inverse

90
Q

When does the cornea lose transparency?

A

If the spacing is disrupted

91
Q

What is keratoconus?

A

Corneal dystrophy, caused is nutritional or metabolic

92
Q

What is the initial disruption in keratoconus?

A

BM and Bowman’s

93
Q

Keratoconus eventually involves what?

A

Significant stromal thinning

94
Q

What type of astigmatism does keratoconus produce?

A

Irregular astigmatism, cannot be corrected with spectacles

95
Q

What may slow the progression of keratoconus?

A

RGP CL

96
Q

What is Munson’s sign in keratoconus?

A

Lower lid conforms to conic shape on down gaze

97
Q

Currently clinical trials are evaluating collagen cross linking to what?

A

Slow disease progression

98
Q

What is collagen cross linking?

A

Riboflavin saturates the cornea and is then activated by ultraviolet light, this increase cross linking between collagen fibrils thus strengthening the cornea and may arrest the progression of keratoconus

99
Q

What is the cellular composition of Descemet’s membrane?

A

Dense CT, acellular

100
Q

What is the BM of corneal endothelium?

A

Descemet’s membrane

101
Q

Descemet’s membrane is highly resistant to ______ ______

A

Proteolytic enzymes

102
Q

Descemet’s membrane has ________ properties

A

Elastic

103
Q

What is the termination of Descemet’s membrane in the corneal periphery?

A

Schwalbe’s line

104
Q

How are the cells in the endothelium arranged?

A

Regular arrangement = endothelial mosaic

105
Q

What % of cells are hexagonal in the endothelium?

A

70-80%

106
Q

The endothelium does not _______; cells just spread out. Cells appear to be in ______ state.

A

Replicate, arrested

107
Q

What are the 4 intercellular junctions in the endothelium?

A

Lateral interdigitations, gap junctions, occluding junctions, and modified hemidesmosomes

108
Q

What are occluding junctions?

A

“Slightly leaky” barrier

109
Q

What are Hassall-Henle bodies?

A

Thickenings in Descemet’s membrane, they are a normal physiological aging change

110
Q

Guttata

A

Deposits in Descemet’s membrane indicative of dysfunction

111
Q

Dua’s layer

A

Recent studies suggest that there is this collagenous layer between stroma and Descemet’s membrane

112
Q

What cells are Dua’s layer composed of?

A

Acellular and composed primarily of collagen type 1

113
Q

The presence of Dua’s layer might be important for what?

A

Current corneal transplant procedures

114
Q

Are there corneal BVs?

A

NO

115
Q

Why are there no corneal BVs?

A

There may be an antiangiogenic agent present

116
Q

What type of sensory innervation is in the cornea?

A

Dense

117
Q

The cornea has about ____ times as many sensory fibers in the tissue than anywhere else in the body

A

400

118
Q

How many bundles of axons enter the corneal periphery?

A

70-80

119
Q

Fibers lose the myelin sheath within ___ mm into cornea

A

1-2

120
Q

What is the innervation pattern of the cornea?

A

Stomal plexus, subepithelial plexus, intraepithelial plexus

121
Q

How many axons are in the stromal plexus?

A

900-1200

122
Q

What happens in the intraepithelial plexus?

A

Schwann cells covering loss as fibers pass through Bowman’s

123
Q

Most receptors in the cornea are what type?

A

Nociceptors

Anatomy and Biochemisty (15 decks)

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