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Ocular Anatomy > Lecture 4: Cornea > Flashcards

Lecture 4: Cornea Flashcards

1
Q

(corneal dimensions) Anterior horizontal diameter:

A

12 mm

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2
Q

(corneal dimensions) Anterior vertical diameter:

A

11 mm

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3
Q

(corneal dimensions) Posterior view:

A

cornea appears circular

H and V diameter: 11.7 mm

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4
Q

is the cornea flatter or steeper in the center?

A

steeper

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5
Q

is the cornea flatter or steeper near the periphery?

A

flatter

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6
Q

(Radius of curvature) Anterior central cornea:

A

7.8 mm

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7
Q

(Radius of curvature) Posterior central cornea:

A

6.5 mm

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8
Q

Central corneal thickness (CCT):

A

0.53 mm or 530 micron

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9
Q

Peripheral corneal thickness :

A

0.71 mm or 710 micron

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10
Q

why are corneal dimensions clinically relevant?

A

Astigmatism: Variation in corneal curvature in various meridians
contributes to astigmatism

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11
Q

Regular astigmatism:

A

steepest and flattest meridians lie

90 degree apart

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12
Q

Irregular astigmatism:

A

steepest and flattest meridian are

not 90 degrees apart (uncommon)

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13
Q

With the rule astigmatism:

A

the steepest curvature lies in V- meridian and the flattest curvature lies in H-meridian

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14
Q

Against the rule astigmatism:

A

the steepest curvature is in H- meridian (not common, ‘WTR to ATR’ in old age due to lens change)

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15
Q

what structure is the principal refracting surface of the eye?

A

cornea

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16
Q

why is the cornea transparent?

A
  1. Due to smooth and regular epithelium
  2. Regular arrangement of stromal fibrils and small
    fibril diameter
  3. Destructive interference of light minimizes light
    scattering (cornea scatter less than 1% of light)
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17
Q

is the cornea avascular or vascular?

A

avascular

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18
Q

the peripheral cornea is continuous with what?

A

The peripheral cornea is continuous with conjunctiva and sclera

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19
Q

Corneal haze:

A

the spacing of stromal fibrils is altered due to edema or due to activated fibroblast, myofibroblast cells (especially after PRK)

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20
Q

how many layers does the cornea have? what are they?

A
  1. Epithelium
  2. Bowman’s layer
  3. Stroma
  4. Descemet’s membrane
  5. Endothelium
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21
Q

how many cell layers thick is the epithelium layer of the cornea? microns?

A

5-7 cell layers thick, approx. 50 micron

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22
Q

the apical surface of the epithelium layer is the superficial layer. How many layers compose this layer and what is the tissue type?

A

2-3 layers of flattened,

squamous

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23
Q

In the epithelium layer of the cornea what layer comes after the apical layer? And how many layers compose that layer?

A

2-3 layers of “wing” cells

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24
Q

how are wing cells attached to each other?

A

Attach to each other by desmosomes and gap junctions.

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25
what layer of cells in the epithelium are the only cells to undergo mitotic division?
basal layer cells
26
The basal surfaces of these cells hold to the underlying Bowman’s layer by what?
hemidesmosome*
27
what 3 layers are in the first corneal layer: epithelium?
apical, wing, and basal
28
how thick is bowman's layer?
8-14 micron thick
29
is bowman's layer a true membrane?
- no it is transition layer to stroma -- not a true membrane (passive) - It’s an acellular membrane
30
what corneal layer is rigid and provides shape to the cornea?
bowman's layer
31
T or F: bowman's layer is resistant to damage by penetrating injury or infection
T
32
is bowman's layer regenerative or non-regenerative?
Non-regenerative: if injured it is replaced by epithelium | (PRK) or stromal scar tissue
33
If the corneal injury goes into Bowman’s layer or deeper, it will heal with what?
a scar
34
what is Keratoconus?
corneal dystrophy due to localized disruptions of Bowman’s layer, stroma thins and weakens and intraocular pressure causes cornea to bulge and take shape of a cone
35
what corneal layer is the thickest?
Stroma: 500 micron thick or 90% of corneal thickness
36
what is the stroma composed of?
Composed of collagen fibrils, keratocytes, extracellular matrix
37
what maintains stroma by synthesizing collagen and extracellular matrix?
Keratocytes
38
are WBC, Macrophage, lymphocytes, PMNs in the stroma normally active or dormant?
dormant - they may become active if the corneal injury is severe
39
Fibril bundles form lamellae, which are regularly spaced, runs where to where?
limbus to limbus, parallel to the corneal surface.
40
Glycosaminoglycans (GAGs):
carbohydrate molecules, hydrophilic, attract and bind water (cornea has 78% water)
41
what is corneal edema?
Over-hydration of cornea results in corneal edema loss of transparency = corneal haze
42
how thick is Descemet's membrane (4th layer)?
5-15 micron thick, in children 5 microns and thickens to 15 microns
43
is Descemet's membrane a true membrane with the ability to regenerate?
yes
44
where does Descemet's membrane terminate? and what does this form?
It terminates at the limbus and forms an important circular structure in angles called “Schwalbe’s line
45
is the Descemet's membrane firmly or weakly attached?
Weak attachments to the neighboring structures (stroma and endothelium) • Can be detached easily
46
how thick is the endothelium layer of the cornea?
5 micron thick
47
what layer is considered the Innermost layer of the cornea?
endothelium
48
what type of cells are covering the entire posterior cornea?
Hexagonal cells
49
do endothelial cells divide?
Endothelial cells do not divide or | replicate, stretch to cover a defect.
50
why does the endothelium layer receive nutrients from the aqueous humor?
The barrier is slightly leaky: allows nutrient flow from the aqueous humor e.g. glucose, amino acids as well as water
51
how is the excess water removed in the endothelium?
Excess water needs to be moved- out by an active metabolic endothelial pump (Na-K-ATPase pump)
52
what are the 3 Endothelial cells densities?
* 1000-2000 cells/mm sq at 80 years * 3000-4000 cells/mm sq in children * 2500-3000 cells/mm sq in adult
53
what is the minimum cell density per mm sq needed for function?
400-700 cells/mm sq minimum needed to function
54
Pleomorphism:
change in cell shape
55
Polymegathism:
change in cell size
56
what are 3 clinical relevances regarding the endothelium?
Hassall-Henle bodies Guttata Contact lens effect
57
Hassall-Henle bodies:
thickening of Descemet’s membrane (DM) bulging into the anterior chamber near the corneal periphery (common finding increases with age)
58
Guttata:
thickening of DM in the central cornea is called guttata (indicative of endothelial dysfunction)
59
Contact lens effect:
pleomorphism and polymegathism were documented after 6-years of GP lens or soft lens wear (cell density remain normal).
60
The cornea is richly innervated by corneal nerves that send what type of signal/ impulse and where?
afferent impulses through the long ciliary nerves (CN V Ophthalmic division).
61
within the cornea are nerves myelinated or unmyelinated?
unmyelinated
62
the cornea acquires a myelin sheath where?
at the limbus
63
does the corneal nerve innervate Descemet’s membrane and the endothelium
Descemet’s membrane and the endothelium are not innervated.
64
what 3 things does the corneal nerve play an important role in?
- Reflex tearing - Blink response - Maintaining healthy epithelium
65
T/F: the corneal nerve is an important consideration for making LASIK flap
T
66
is the corneal nerve damaged during PRK and LASIK
yes
67
how long does it take corneal nerves to regenerate after refractive surgery?
3-9 months
68
T/F: Diabetes patients may have reduced corneal nerves
T
69
what are Palisades of Vogt?
- Radial projections of fibrovascular tissue in spoke-like fashion around the corneal periphery
70
what does the interpalisade region of Palisades of Vogt contain?
The interpalisade region contain thickened epithelium, limbal stem cells reside here
71
(Palisades of Vogt) Limbal stem cell deficiency:
Loss of stem cells leading to corneal neovascularization and corneal opacity
72
Pinguecula:
Slightly elevated mass of modified conjunctival tissue - Usually at 3 and 9 o'clock - Change in the submucosal layer - Epithelium unchanged
73
Pterygium:
Fibrovascular, triangular over- growth of bulbar conjunctiva - onto cornea usually progressive - Induces astigmatism and vision change (drop-in UCVA, BCVA) - As it progresses onto the cornea, It damages the corneal epithelium, as well as bowman’s layer, is compromised

Ocular Anatomy (15 decks)

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