Exam 1 Remington- Cornea Flashcards Preview

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Flashcards in Exam 1 Remington- Cornea Deck (123):
1

What are the two functions of the cornea?

Transmission and Refraction

2

What is refraction of the cornea dependent on?

Curvatures, length, different indices

3

Anterior diameter of the cornea

12 mm horizontal, 11 mm vertical

4

Posterior diameter of the cornea

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

5

Central thickness of the cornea

0.53 mm

6

Peripheral thickness of the cornea

0.71 mm

7

Anterior radius of curvature of the cornea

7.8 mm

8

Posterior radius of curvature of the cornea

6.5 mm

9

_____ radius of curvature means a steeper curve

Shorter

10

What is regular astigmatism?

Principle meridians 90 degrees apart

11

What are 3 types of regular astigmatism?

WTR, ATR, and oblique

12

What is WTR astigmatism?

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

13

What is ATR astigmatism?

Horizontal meridian is steepest

14

What is oblique astigmatism?

Steepest meridian at 45 or 135 degrees

15

What is irregular astigmatism?

Principle meridians are not 90 degrees apart

16

How is irregular astigmatism corrected?

Contact lenses

17

What is the function of the plasma membrane lipid bilayer?

Controls molecular entrance and exit

18

What is the function of the cytoskeleton?

Structure and intercellular transport

19

What is the function of ribosomes?

Manufactures protein

20

What is the function of the endoplasmic reticulum?

Protein/lipid synthesis

21

What is the function of the Golgi apparatus?

Package proteins

22

3 types of cellular transport

Diffusion, facilitated diffusion, active transport

23

What do aquaporins do?

Move water

24

What type of channels are aquaporins?

Bidirectional in the cornea and lens

25

3 types of cell surfaces

Apical, lateral, and basal

26

What is a basal cell surface?

Sits on basement membrane, connective tissue

27

The basement membrane consists of what 2 types of lamina?

Basal and reticular

28

Basal lamina is secreted by what cell?

Epithelial

29

Reticular lamina secreted by what cell?

CT layer

30

What are the 2 shapes of intercellular junctions?

Zonular and macular

31

Zonular

Belt-like goes all the way around cell

32

Macular

Spot-like

33

What are the 2 types of intercellular junctions?

Adhering and occluding

34

Adhering intercellular junction

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

35

Occluding intercellular junction

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

36

What is a terminal bar?

Adjacent ZO + ZA

37

Desmosomes

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

38

Hemidesmosomes

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

39

Gap junctions

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

40

Connexon

Transmembrane channel or pore

41

What does a connexon do?

Joins cytoplasm of adjoining cells

42

A connex___ is composed of 6 protein connex___

-on, -in

43

What do gap junctions do?

Permits passage of small molecules, nutrients, and ions

44

Glycocalyx

Gycoprotein covering surface of the cell

45

The corneal epithelium consists of what kind of cells?

Stratified squamous

46

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

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

47

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

Semi-permeable membrane

48

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

Evaluates the barrier function of the surface layer

49

What happens when fluorescein is instilled in the tear film?

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.

50

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

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

51

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

Wing cell layer

52

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

Basal layer

53

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

Desmosomes, gap junctions, hemidesmosomes

54

What secretes the basal lamina portion of the BM?

Basal layer

55

In hemidesmosomes, fibrils attach to _____ in stroma

Plaques

56

What do plaques contain?

Laminin

57

What are two causes of recurrent corneal erosion?

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

58

Dystrophy

Condition caused by defective nutrition or metabolism, also malformed hemidesmosomes

59

What are signs and symptoms of recurrent corneal erosion?

Areas of sloughed epi, pain

60

What is the treatment of recurrent corneal erosion?

Bandage contact lens and corneal puncture

61

What does corneal puncture do?

Stimulates BM adhesion

62

Epithelial replacement is _______

Constant

63

Where does cell division occur in the corneal epithelium?

Basal layer

64

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

Stem cells in the limbus

65

How do cells move in epithelial replacement?

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

66

Where are surface cells sloughed?

Into tear film

67

What is the cellular composition of Bowman's layer?

Dense irregular CT, acellular

68

Bowman's layer is considered a ______ layer

Transition

69

How is Bowman's layer compared to the stroma?

Smaller and less regular fibers than stroma

70

Bowman's layer is produced _____ and cannot be _______

Prenatally, regenerated

71

What is a pterygium?

Conj invades corneal tissue, Bowman's layer is lysed

72

What is another name for stroma?

Substantia propria

73

What is the cellular composition of stroma?

Regular dense CT, collagen fibrils, fibroblasts, ground substance

74

What is lamellae?

Bundles of collagen

75

What is the orientation of lamellae?

Fibers are parallel to surface

76

What is the extent of fibers for the lamellae?

Fibers extend from limbus to limbus

77

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

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

78

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

Fibroblasts= keratocytes

79

What junctions are fibroblasts joined by in the stroma?

Gap junctions (can get between cells quickly)

80

What is ground substance composed of?

Proteoglycans and glycosaminoglycans (GAGs)

81

What do proteoglycans so?

Increase tensile strength

82

What are GAGs?

Negatively charged side chains

83

Are GAGs hydrophilic or hydrophobic?

Hydrophilic

84

What do GAGs do?

Maintain component spacing

85

What is the theory of transparency?

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

86

How are fibers arranged in the theory of transparency?

Fibers arranged in a regular lattice pattern

87

_____ interference occurs in the theory of transparency

Destructive

88

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

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

89

What is the relationship between destructive interference and light scatter?

Inverse

90

When does the cornea lose transparency?

If the spacing is disrupted

91

What is keratoconus?

Corneal dystrophy, caused is nutritional or metabolic

92

What is the initial disruption in keratoconus?

BM and Bowman's

93

Keratoconus eventually involves what?

Significant stromal thinning

94

What type of astigmatism does keratoconus produce?

Irregular astigmatism, cannot be corrected with spectacles

95

What may slow the progression of keratoconus?

RGP CL

96

What is Munson's sign in keratoconus?

Lower lid conforms to conic shape on down gaze

97

Currently clinical trials are evaluating collagen cross linking to what?

Slow disease progression

98

What is collagen cross linking?

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

What is the cellular composition of Descemet's membrane?

Dense CT, acellular

100

What is the BM of corneal endothelium?

Descemet's membrane

101

Descemet's membrane is highly resistant to ______ ______

Proteolytic enzymes

102

Descemet's membrane has ________ properties

Elastic

103

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

Schwalbe's line

104

How are the cells in the endothelium arranged?

Regular arrangement = endothelial mosaic

105

What % of cells are hexagonal in the endothelium?

70-80%

106

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

Replicate, arrested

107

What are the 4 intercellular junctions in the endothelium?

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

108

What are occluding junctions?

"Slightly leaky" barrier

109

What are Hassall-Henle bodies?

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

110

Guttata

Deposits in Descemet's membrane indicative of dysfunction

111

Dua's layer

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

112

What cells are Dua's layer composed of?

Acellular and composed primarily of collagen type 1

113

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

Current corneal transplant procedures

114

Are there corneal BVs?

NO

115

Why are there no corneal BVs?

There may be an antiangiogenic agent present

116

What type of sensory innervation is in the cornea?

Dense

117

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

400

118

How many bundles of axons enter the corneal periphery?

70-80

119

Fibers lose the myelin sheath within ___ mm into cornea

1-2

120

What is the innervation pattern of the cornea?

Stomal plexus, subepithelial plexus, intraepithelial plexus

121

How many axons are in the stromal plexus?

900-1200

122

What happens in the intraepithelial plexus?

Schwann cells covering loss as fibers pass through Bowman's

123

Most receptors in the cornea are what type?

Nociceptors