Ocular: Cornea 1 And 2 Flashcards
1
Q
Major concepts of the cornea:
A
-part of fibrous tunic
-transparent
-tough
-highly innervated
-avascular
-major refractive component of the eye
2
Q
Cornea is the anterior ____th of the eye
A
1/6th
3
Q
Area of cornea:
A
1.3 cm2
4
Q
Is the cornea or the sclera steeper?
A
Cornea
5
Q
Radius of curvature of posterior cornea:
A
6.5 mm
6
Q
Radius of curvature of anterior cornea:
A
7.8mm
7
Q
Range of horizontal corneal dimensions anteriorly:
A
11.7-12.6mm
**appears elliptical
8
Q
Range of vertical corneal dimensions anteriorly:
A
10.6-11.7mm
9
Q
Vertical and horizontal dimensions of cornea posteriorly:
A
11.7 horizontally and vertically
*cornea appears circular
10
Q
Overall dioptric power ranges of the cornea:
A
+43.1D to +48.8D
-3/4th refractive power of eye
11
Q
Index of refraction of the cornea
A
1.376
12
Q
Astigmatism
A
Unequal curvature of the cornea that prevents light from being focused to a single point on the retina
13
Q
Regular astigmatism:
A
Flat and steep meridians are 90 degrees apart
14
Q
Types of regular astigmatism:
A
-with the rule
-against the rule
-oblique
15
Q
With the rule astigmatism
A
Steeper in vertical meridian
16
Q
Against the rule astigmatism
A
Steeper curvature in horizontal meridian
17
Q
Oblique astigmatism
A
Steeper curvature in oblique axis
18
Q
Irregular astigmatism
A
Steepest and flattest meridians are not 90 degrees apart
19
Q
Lenticular astigmatism
A
Unequal curvature of the lens
20
Q
Average central corneal thickness:
A
O.52mm
21
Q
Average peripheral corneal thickness:
A
0.70mm
22
Q
The thicker a persons cornea the _______ their IOP pressure measurement will be
A
Higher
23
Q
The thinner a persons cornea, the _________ their IOP measurement will be
A
Lower
24
Q
True IOP
A
the actual fluid pressure inside the eye measured by a tool that accounts for the biomechanical properties of the cornea
25
Pachymeter
Measures central corneal thickness using ultrasound
26
When might you want to use a Pachymeter on a patient ?
If the IOP measurement seems off, its used to measure true IOP esp if cornea is too thick or too thin
27
Bulbar limbus:
Fascia bulbi (tenon’s capsule) strongly adheres to episclera and conjunctiva
28
Corneoscleral limbus:
-Juncture of cornea and sclera
-1-2mm wide
29
Conjunctival limbus:
Conjunctiva extends 1mm beyond corneoscleral limbus
30
Optical zone of cornea is the central ___mm
4mm
31
5 layers of the cornea:
-anterior epithelium
-bowman’s layer
-stroma
-descemets membrane
-endothelium
32
The tear film sits ________ to the cornea and consists of ___ layers
Anterior, 3 layers
33
Three layers of the tear film:
-lipid/oily layer
-aqueous layer
-mucous layer
34
Where does lipid/oil layer of tear film come from?
Meibomian glands in the palpebrae and caruncle
35
Where does aqueous layer in the tear film come from?
Lacrimal gland
36
Where does mucous layer in the tear film come from?
Goblet cells in the conjunctiva
37
Why is the oily layer important?
Prevents the aqueous layer from evaporating
38
Why is the mucus layer important?
Decreases the surface tension and provides a smooth, wearable surface for the aqueous layer
39
Rate of tear production:
1.2 microliters/minute
40
Volume of tears:
6.2 +/- 2 microliters
41
Corneal epithelium is made up of what type of tissue? And how thick is it?
Stratified squamous epithelium, 50-60 microns thick
42
Corneal epithelium is continuous with the…..
Bulbar conjunctival epithelium
43
Corneal epithelium consists of ____________ and ______________cells and rests on a ______________membrane
Melanocytes and langerhan’s cells, basement membrane
44
Epithelium is composed of ___ - ___ layers and what type of tissue makes it up?
5-7 layers, non-keratinized, non-secretary stratified squamous epithelium
45
Apical (superficial) layer of epithelium is 1-2 layers of _________, ___________ cells near the surface
Flattened, squamous cells
46
2-3 layers of _____ cells attach to each other by desmosomes and gap junctions
“Wing” cells
47
The basal layer of cells in the epithelium are the only layer of cells in the corneal epithelium that undergo ________ __________ and are __________shaped
Mitotic division, columnar
48
Why are microvilli and microplicae important?
They pick up O2 from the air that is dissolved in the tears and assist in maintained the mucous lateral for adherence of aqueous layer
49
Loss of microvilli and microplicae can occur following…
Use of contact lenses
50
Loss of surface microvilli can lead to …
Transient dry eye symptoms until new cells reach the surface and develop microvilli
51
Where are tight junctions found on the apical surface of epithelium?
Between the lateral surfaces of apical cells!!
52
How to wing cells attach to adjacent cells?
They attach through desmosomes
53
How do wing cells communicate with adjacent cells?
Gap junctions
54
basal cells, like wing cells, also are attached to adjacent basal cells via _____________, and communicate via _____________
Desmosomes, gap junctions
55
How do basal cells attach to basement membrane?
Hemidesmosomes break, leaving anchoring fibrils form basal cells holds attachment
56
Why are anchoring fibrils important for basal cells?
They form the complex responsible for the firm attachment of the epithelium to underlying stroma
57
Corneal abrasion:
-scratch on the eye’s cornea
-usually painful but not severe
-commonly caused in sports by a scratch from fingernail
58
What are palisades of Vogt? Why are they important?
-Series of ridges in the corneoscleral limbus
-they house stem cells for corneal epithelium
59
Bowman’s layer is believed to provide ___________ _________ and is made up of ________ _________ ___________ ___________
Structural support, randomly arranged collagen fibrils
60
Is bowman’s layer acellular?
YES
61
How thick is bowman’s layer?
8-12 micrometer thick
62
Bowman’s layer contains ________ for passage of corneal nerve fibers
Channels (or pores)
63
Can the bowman’s layer be striped away from the stroma? Why or why not?
Cannot be because it is a continuous sheet
64
Can bowman’s layer regenerate?
NO
65
When is bowman’s layer formed?
Prenatally
66
If bowman’s layer is damaged, what replaces it?
Thickened epithelium (aka epithelial facet)
67
Does bowman’s layer contribute to bulbar conj?
NO
68
Why is bowman’s LAYER no longer called bowman’s MEMBRANE?
Because bowman’s “membrane” was found to be PAS negative, which is NOT a true basement membrane ….and no gags
69
What percent of corneal thickness is made up by the stroma?
90%
70
How thick is the stroma?
450-500 micrometers
71
What is the stroma made up of?
Collagen, keratocytes, and ground substance; where the collagen is organized in lamellae
72
In the stroma, what pulls aqueous humor into the cornea?
Glycosaminoglycans (GAGS)
73
In the stroma, what is interspaced between lamella and why?
Keratocytes, to maintain ground substance and collagen
74
How do keratocytes communicate with each other?
Gap junctions
75
Descemet’s membrane is the _____________ ____________ of endothelium
Basement membrane
76
Descemet’s membrane thickness throughout life from __micrometers to ___ micrometers
3 to 15 micrometers
77
Does descemets membrane regenerate if damaged?
YES
78
In Descemet’s membrane what is laid down before birth?
The anterior banded zone
79
In the Descemet’s membrane, what is laid down after birth?
Posterior unbanded zone
80
Where does Descemet’s membrane terminate?
At the schwalbe’s line ABRUBTLY
81
Hassall-Henle warts
transparent growths on the peripheral cornea and is normal with age
82
Corneal guttata
Transparent growths in the central cornea that indicate abnormal function of endothelium and can indicate endothelial dystrophy
83
Corneal endothelium is __-___micrometers thick
4-6
84
Corneal endothelium is a monolayer composed of about_________to _______cells
400,000 to 500,000 cells
85
Corneal endothelium cells appear ____ and ______ in shape and their apex faces the ________ chamber
Flat, hexagonal, anterior chamber
86
Corneal endothelium is linked together by ____________ and form ____________ to communicate with adjacent cells
Macula occludens, gap junctions
87
How does corneal endothelium maintain hydration?
By pumping aqueous humor out of the cornea
88
Loss of cells in the corneal endothelium can cause..
Change sin size and shape
89
If the pump action in corneal endothelium is not occurring what results?
Stroma edema
90
As corneal endothelial cells become stressed they __________
Dropout
91
When cells dropout from corneal endotheialium, the remaining cells compensate by…
Expanding in size and shape
92
When cells in corneal endothelium dropout, there is…
Less pump available to counterbalance leak of aqueous humor into corneal stroma
93
Is cornea vascular or avascular?
AVASCULAR
94
Where are nutrients derived from?
Tear film and aqueous humor, but also rely on nutrients from vasculature at peripheral cornea
95
Vasculature at peripheral cornea where we can get nutrients:
-superficial pericorneal plexus
-deep pericorneal plexus
96
Is cornea innervated?
YES! One of the most highly innervated structures in the body
97
Corneal sensitivity is ________ times greater than that of integument
300-600 times
98
Sensory innervation from the cornea is conveyed via:
Long posterior ciliary nerves
99
Where do the LPCN course and form?
In the suprachoroidal space and form an annular plexus of smaller branches within the corneoscleral limbus
100
Small radial branches extend into the middle and anterior stroma and form a _________________ below the bowman’s layer
Subepithelial plexus
101
If nerve fibers in the subepithelial plexus lose their myelin sheath they become naked and pass through the bowman’s layer to enter corneal epithelium where they form an ______________ ______________
Intraepithelial plexus
102
Where are sensory fibers not present within the cornea?
Posterior stroma, Descemet’s membrane, and corneal endothelium
