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Ocular Block 6 > Cornea > Flashcards

Cornea Flashcards

1
Q

Major concepts about the cornea

A
  • part of the fibrous tunic
  • transparent
  • tough
  • highly innervated
  • avascular
  • major refractive component of the eye
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2
Q

Cornea is the anterior _____ of the eye

A

1/6th

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3
Q

Which has steeper curvature, cornea or sclera?

A

Cornea

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4
Q

What does the merger of the cornea and sclera form?

A

External scleral sulcus

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5
Q

Where does vasculature abruptly end in eye

A

Corneoscleral limbus

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6
Q

Anterior view of cornea shape

A

Oval

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7
Q

Diameter of horizontal anterior cornea

A

11.7-12.6mm

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8
Q

Diameter of vertical anterior corneal

A

10.6-11.7mm

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9
Q

What is the shape of the cornea posteriorly

A

Perfect sphere

11.7

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10
Q

Radius of curvature of the posterior cornea

A

6.5mm

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11
Q

Radius of curvature of the anterior cornea

A

7.8mm

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12
Q

Overall power of cornea

A

Ranges from +43.1D to +48.8D

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13
Q

Index of refraction of cornea

A

1.376

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14
Q

Unequal curvature of the cornea that prevents light from being focused to a single point on the retina

A

Astigmatism

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15
Q

Flat and steep meridians are 90 degrees apart

A

Regular astigmatism

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16
Q

Steeper in vertical meridian, like a football laying on its side

A

With the rule astigmatism

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17
Q

Steeper curvature in the horizontal meridian, like a football standing on its tip

A

Against the rule astigmatism

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18
Q

Steeper curvature in oblique axis

A

Oblique astigmatism

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19
Q

Steepest and flattest meridians are not 90 degrees apart

A

Irregular astigmatism

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20
Q

Unequal curvature of the lens

A

Lenticular astigmatism

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21
Q

Average CCT

A

0.52mm

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22
Q

Average peripheral corneal thickness

A

0.70mm

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23
Q

Thicker corneas and IOP reading

A

Higher than normal IOP reading

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24
Q

Thinner corneas and IOP reading

A

Lower IOP reading

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25
Q

Measures central corneal thickness using ultrasound

A

Pachymeter

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26
Q

When might you use a pachymeter on a patient

A

Suspect glaucoma but getting normal IOP reading, or when someone looks normal but gets higher IOP readings

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27
Q

Fascia Bulbi (Tenon’s Capsule) strongly adheres to episclera and conjunctiva. Forms so key of eye

A

Bulbar limbus

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28
Q

Juncture of cornea and sclera

A

Corneoscleral limbus

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29
Q

Conjunctiva extends 1mm beyond corneoscleral limbus. Arcades stop here

A

Conjunctival limbus

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30
Q

Central 4mm of the cornea

A

Optical zone

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31
Q

What is the cornea predominantly made of

A

Extracellular material

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32
Q

How many layers to the anterior epithelium

A

4 layers

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33
Q

How many layers to the posterior epithelium

A

1

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34
Q

What is the bulk of the cornea

A

Stroma

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35
Q

Layers of cornea from front to back

A
  • tear film
  • anterior epithelium
  • bowmans layer
  • stroma
  • descemet’s membrane
  • endothelium
  • aqueous humor
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36
Q

How thick is tear film

A

7 microns

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37
Q

Volume of tear film

A

6.2 +/- 2 microliters

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38
Q

What is contained in the tear film

A

Electrolytes, metabolites, proteins, and lipids

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39
Q

What are the 3 layers of the tear film from anterior to posterior

A

Lipid layer
Aqueous layer
Mucous layer

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40
Q

Secreted by meibomian glands in the palpebrae and carbuncle. Prevents evaporation of aqueous layer

A

Lipid layer

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41
Q

Secreted by the lacrimal gland

A

Aqueous layer

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42
Q

Secreted by goblet cells in the conj. Helps aqueous stick

A

Mucous layer

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43
Q

How do the oily and the mucous layer help the aqueous layer

A

The oily layer prevents the aqueous layer from evaporating, while the mucous layer decreases surface tension and provides a smooth, wetable surface for the aqueous layer

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44
Q

What helps join the mucous layer of the tear film

A

Glycocalyx

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45
Q

Overflowing of tears

A

Epiphora

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46
Q

Why do people get epiphora

A

Overproduction of tears because lipid layers is absent and causes evaporation

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47
Q

What helps people who have problems with the lipid layer

A

Hot compress to help meibomian glands express lipid layer

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48
Q

What is the corneal epithelium composed of

A

Stratified squamous epithelium

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49
Q

How thick is the corneal epithelium

A

50-60 microns

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50
Q

What is the corneal epithelium continuous with

A

Bulbar conj

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51
Q

What layer of the cornea contains melanocytes and langerhans cells?

A

Peripheral part of the corneal epithelium

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52
Q

What does the corneal epithelium rest on

A

Basement membrane, allows for migration of basal cells

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53
Q

How many layers of cells is the corneal epithelium composed of

A

5-7, non keratinized, non secretory.

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54
Q

What are the cells from superficial to deep of the corneal epithelium

A

Apical
Wing
Basal

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55
Q

Apical layer of the corneal epithelium

A

1-2 layers of flattened, squamous cells near the surface

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56
Q

What are the wing cells of the corneal epithelium

A

2-3 layers

Attach to each other by desmosomes and gap junctions

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57
Q

Basal cells of the corneal epithelium

A

A single layer of columnar cells

-are the only cell of the corneal epithelium that undergo mitotic divsion.

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58
Q

What is the basal surface of the basal cells of the corneal epithelium attached to?

A

Held to the underlying bowmans layer by hemidesmosomes

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59
Q

What do the microvilli and microplicae on the surface of the corneal epithelium do?

A

Pick up O2 from the air that is dissolved in tears, assist in maintaining mucous layer for adherence of aqueous layer.

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60
Q

Loss of the microvilli and microplicae on the corneal epithelium

A

Can occur following regular use of CL, leading to transient dry eye symptoms until new cells reach the surface and develop microvilli

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61
Q

Where does the mucin layer of the tear film attach to the cornea

A

Microplicae on the corneal epithelium

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62
Q

What kind of junctions between the surfaces of apical cells in the corneal epithelium?

A

Tight junctions. Represent a semipermeable barrier of the corneal epithelium. Zone occludens take 1 hour to replace

This forms barrier, nutrients have to go through the cell

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63
Q

How many wing cells centrally (corneal epithelium)?

A

2-3 layers

64
Q

How many wings cells peripherally (corneal epithelium)?

A

4-5

65
Q

Shape of wing cells in corneal epithelium

A

Posterior surface is concave and hte anteiror surface is convex

66
Q

How are wing cells attached to each other

A

Desmosomes, also have gap junctions

67
Q

How does the shape of the wing cells change as they move towards surface

A

Beceom progressively flatter due to pressure from eyelids

68
Q

How do basal cells attach to wing cells

A

Desmosomes

69
Q

How do basal cells communicate with each other

A

Gap junctions

70
Q

How are basal cells attached to one another

A

Desmosomes

71
Q

This formed the complex responsible for the firm attachment of the epithelium to the underlying stroma

A

The hemidesmosomes and its associated anchoring fibrils

72
Q

What happens to the anchoring filaments that are attached to the basal cells of the epithelium during DM?

A

BM becomes thick, anchoring filaments cant hold on well and cause BM issues, sloughing issues

73
Q

Are there free nerve endings in the basal layer of the corneal epithelium?

A

Yes

74
Q

Herpes simplex keratitis

A
  • herpes hangs out in the DRG

- forms this dendritic structure because of gap junctions in epithelium via nerve

75
Q

Contact solutions and cornea

A

Preservatives in contact lens solutions can be toxic to the cornea

76
Q

A crutch on the eyes cornea, usually painful, but not severe. Commonly caused in sports by a scratch from the fingernail

A

Corneal abrasion

77
Q

Symptoms of corneal abrasion

A

Pain
Feeling that something is in the eye
Tearing
Discomfort when blinking

78
Q

First reaction for people when they get a corneal abrasion?

A

Rub their eye

79
Q

What to do for corneal abrasion

A

Rinse with clean water or saline, do not rub

80
Q

Treatment for corneal abrasion

A

See eye care prof
Aggressive lubrication
Antibiotic ointment or drops

81
Q

How deep does a corneal abrasion go?

A

Surface epithelium scratch only!

82
Q

What is used to assess the size and depth of he corneal abrasion?

A

Fluorescein dye

83
Q

Punctuate epitheliopathy

A

Lower 1/3rd of corneal stains with fluoroscein. Sleeping with eyes ope, looking down when reading

84
Q

Peripheral margin of cornea. Stem cell depot. Basal cells start here, move down and out

A

Palisades of Vogt

85
Q

What are some examples of corneal epithelial dystrophies

A

Meesmans dystrophy
Subepithelial mucinous dystrophy
Gelatinous drop-like dystrophy

86
Q

Is bowmans layer a basement membrnae?

A

No

87
Q

Role of bowmans layer

A

Believed to provide structural support

88
Q

Make up of Bowmans layer

A
  • Randomly oriented collagen fibers with no keratocytes (acellular)
  • 8-12 microns thick
  • contains channels for passage of nerve fibers
  • cannot be stripped away from the stroma as a continuous sheet
89
Q

Can bowmans layer regenerate?

A

No, it is formed prenatally. If damaged it is replaced by thickened epithelium

90
Q

Where does the bowmans layer end

A

At limbus

91
Q

Why is bowmans layer no longer called bowmans membrane?

A

Because it does not stain with periodic acid-Schiff.

PAS negative

92
Q

Corneal dystrophy of bowmans layer type 1

A

Confined to bowmans

93
Q

What is 90% of corneal thickness?

A

Stroma

94
Q

How thick is stroma

A

450-500 microns

95
Q

Make up of stroma

A
  • Collagen organized into layers (lamellae).
  • GAGs
  • keratocytes between lamella
96
Q

What do GAGs do in stroma

A

Pull aqueous humor into cornea

97
Q

What do keratocytes do in stroma

A

Maintina ground substance and collagen. Active in inflammation

98
Q

Flats cells, reside between stromal lamellae, and communicate via gap junctions

A

Keratocytes

99
Q

Light scattering and hte stromal lamella

A

1% of light gets scattered.
Spacing is 1/2 wavelnegth of visible light

damage/swelling causes more light scatter, appears opaque or white

100
Q

What is thinning of the stroma called

A

Keratocconus

101
Q

Keratoconus

A

Thinning of stroma. Causes irregular astigmatism, typically bilateral. Misshapen because the stroma cant resist IOP

102
Q

Munson’s sign

A

In advanced keratoconus the corneal protrusion may cause angulation of the lower lid on down gaze

103
Q

Difference between corneal abrasion and corneal ulcer

A

Abrasion is in epithelium and ulcer is in the stroma.

104
Q

How can you get herpes in the stroma as well as the epithelium?

A

Because herpes rides on the nerves and the nerve fibers pass through anteiror stroma

105
Q

Pseudomonas keratitis

A
  • CL wearers get it
  • penetrates though BM
  • corneal melt
  • goes through the epithelium and the stroma
106
Q

Corneal hydrops

A

Descemets membrane rupture

107
Q

Types of corneal stromal dystrophies

A
  • lattice dystrophy type I
  • granular dystrophy type II
  • schnyder’s dystrophy type I
  • congenital stromal dystrophy
108
Q

Arcus senilis

A

Lipid deposits in stroma. Usually around limbus

109
Q

What does it mean if the arcus senilis is monocular?

A

Carotid artery blockage on the side with the eye that does not have arcus senilis.

110
Q

Basement membrane of the corneal endothelium

A

Descemet’s membrane

111
Q

Descemet’s membrane and age

A

Thickens throughout life from 3 microns to 15 mictrons

112
Q

What happens if decemet’s membrane is damaged?

A

Regenerates

113
Q

Anterior banded zone of descemets membrane

A

Laid down before birth

114
Q

Posterior unbranded zone of descemet’s membrane

A

Laid down after birth

115
Q

How does descemet’s membrane terminate?

A

Abruptly as Schwalbe’s line

116
Q

Wilson’s disease

A

Liver disease, lenticulate nucleus of brain

-produces Kayser-Fleisher Ring (copper deposits in Descemet’s membrane)

117
Q

Hassall-Henle bodies

A

Occur in peripheral cornea and is a normal occurrence with age

118
Q

Corneal guttata

A

Occur in central cornea and indicate abnormal function of endothelium. Indicate endothelial dystrophy

119
Q

Difference between Hassall-henle bodies and Guttata?

A

Hassan-henle is in peripheral cornea and Normal with age

Guttata in central corneal and indicate endothelial dystrophy

120
Q

Thickness of corneal endothelium

A

4-6 microns thick

121
Q

How many cell layers is corneal endothelium

A

1

122
Q

Where does the apex of the corneal endothelium face

A

Anterior chamber

123
Q

Where does the basal portion of the corneal endothelium face?

A

Secreted Descemet’s membrane

124
Q

How are the cells of the corneal endothelium joined?

A

Macula occludens (leaky barrier), form gap junctions with neighboring cells

125
Q

What do the cells of the corneal endothelium do?

A

Pump aqueous humor out of the cornea to maintain hydration (pump leak system)

126
Q

Aqueous and the corneal endothelium

A
  • aqueous leaks in from anterior chamber

- cells pump aqueous humor out of the cornea to maintain hydration (pump leak system)

127
Q

Minimum number of cells in corneal endothelium to maintain normal function

A

400-700 cells/mm2

128
Q

Loss of cells in corneal endothelium

A

Can cause changes in size (polymegathism) and shape (pleiomorphism)

129
Q

No pump action in the corneal endothelium results in what

A

Stromal edema

130
Q

Do corneal endothelial cells regenerat?

A

No

131
Q

Breakdown of pump leak system in corneal endothelium

A

As corneal endothelial cells become stressed, they drop out. Remaining cells expand in size and shape to compensate. Less pump available to counterbalance leaks of aqueous humor into corneal stroma, causing chronic endothelial edema

132
Q

Types of corneal endothelial dystrophy

A
  • Fuch’s endothelial dystrophy
  • posterior polymorphous dystrophy
  • congenital hereditary endothelial dystrophy
133
Q

Vasculature of the cornea

A

None

134
Q

How does cornea get nutrients

A

Derived from the tear film and aqueous humor, and vasculature at peripheral cornea.

135
Q

What is the vasculature at the peripheral cornea

A

Superficial pericorneal plexus (conj)

Deep pericorneal plexus (episclera)

136
Q

Lymphatic of cornea

A

None

137
Q

How many anterior ciliary artery are there?

A

7

138
Q

What do anterior ciliary arteries give rise to

A

Anterior and posterior conj arteries

139
Q

Ciliary flush

A

If it is a more red color, its is the superficial pericorneal plexus of the cornea

If it is more pink, it is the deeper pericorneal plexus involving the iris

140
Q

Corneal neovascularization

A

Poor CL wearer

Eye becomes hypoxia, blood vessels grow forward in center of cornea

141
Q

Drain to muscular veins in the rectus muscles

A

Anteiror ciliary veins

142
Q

What is the most highly innervated structure in the body

A

Cornea

143
Q

Corneal sensitivity

A

300-600 times that of the skin

144
Q

Sensory innervation of cornea

A

Conveyed via the long posterior ciliary nerves

145
Q

How does the long posterior ciliary nerve course

A

In the subarachnoid space and forms an annular plexus of smaller branches within the region of the corneoscleral limbus

146
Q

Small radial branches extend into the middle and anteiror stroma and form a ____________ just below bowmans layer

A

Subepithalial plexus

147
Q

Where are the nerves of the cornea located

A

Anterior stroma, bowmans, and epithelium

148
Q

Photorefrctive keratectomy

A

-corneal epithelium is debriefed with surgical tool
-ablate anterior stroma
-bandage contact lens placed over cornea
-re-epitheliztion
=painful for first 24 hours

149
Q

Laser in situ keratomileusis (LASIK)

A
  • flap created and folded back
  • anterior stroma ablated using laser
  • flap replaced
150
Q

Radial incisions cut into stroma to flatten the cornea

A

Radial keratotomy

151
Q

Scleral contact lenses

A

Large diameter RGP CL that vaults the cornea and rests on the bulbar conj and underlying sclera

152
Q

Who could benefit from scleral CL?

A
  • irregular astigmatism
  • penetrating keratoplasty
  • keratoconus
  • pellucid marginal degeneration
  • high refractive error
  • dry eye
  • autoimmune disease
  • graft versus host disease
  • aphakia
153
Q

How do scleral CL work

A

Liquid reservoir (non preserved saline solution) neutralizes irregular corneal surface e

154
Q

Vault height in scleral lens

A

The proper sag height or vault is important to ensure teat lens reservoir adequately covers the entire cornea

155
Q

How do you assess vaulting of scleral lens

A

Fluorescein is mixed with saline to assess it and the clearance of scleral contact lens over the corneal surface and limbus

156
Q

Tear reservoir of scleral contact lenses

A

Must bathe the cornea from apex of the cornea to the limbus

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