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