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OD2 (S1&2) > AED - Corneal Ectasia - Week 11 > Flashcards

AED - Corneal Ectasia - Week 11 Flashcards

1
Q

Is bowmans membrane a basement membrane like descemets membrane? Explain its structure in this regard.

A

It is not
It is an acellular layer composed of randomly arranged collagen fibres

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2
Q

How thicc is the corneal stroma typically?

A

500μm

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3
Q

What is corneal ectasia characterised by? List three things that contribute to this.

A

Corneal conditions that are characterised by progressive thinning of the corneal stroma
-biochemical weakening
-increased corneal curvature
-irregular astigmatism

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4
Q

List three classifications of corneal ectasia and give an example each.

A

Degenerative
-keratoconus
-pellucid marginal degeneration
Congenital anatomy
-keratoglobus
Mechanical trauma such as post-surgery
-iatrogenic ectasia

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5
Q

Is keratoconus progressive? Is it symmetrical or asymmetrical? Is it inflammatory?

A

Progressive, typically asymmetrical, and non-inflammatory

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6
Q

What is keratoconus characterised by? Is it uni- or bilateral?

A

Progressive thinning of the axial corneal stroma
It is bilateral

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7
Q

What condition is the most common primary corneal ectasia?

A

Keratoconus

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8
Q

In what regions is the prevalence of keratoconus higher?

A

Regions where cosanguinity occurs

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9
Q

What is the onset of keratoconus? When does it stabilise? Does its clinical course vary significantly or not?

A

Typical onset at puberty
Stabilises ~35-40yoa
Clinical course varies significantly

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10
Q

List 6 associations with keratoconus. Are associations common or is it an isolated ocular finding?

A

Most commonly an isolated ocular finding
Possible associations include:
-atopy (vernal, athsma, eczema)
-leber’s congenital amaurosis
-retinitis pigmentosa
-down’s syndrome
-connective tissue disorders
-mitral valve prolapse

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11
Q

What is the aetiology and pathogenesis of keratoconus?

A

Uncertain

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12
Q

What is the mode of inheritance for keratoconus? Does it have complete or variable penetrance?

A

Autosomal dominant with variable penetrance

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13
Q

What does the link between keratoconus and connective tissue disorders suggest?

A

A possible genetic abnormality in connective tissues

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14
Q

What do family members of a keratoconic individual typically have?

A

30-50% have subtle topographic abnormalities

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15
Q

Explain two biochemical abnormalities of proteinases in keratoconus.

A

Increased proteinase activity
Decreased activity of proteinase inhibitors

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16
Q

How does interleukin-1 affect keratocytes (3)?

A

It is a key modulator of keratocyte proliferation, differentiation, and death

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17
Q

What is interleukin-1 produced by in the eye (2)?

A

Epithelium and endothelium

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18
Q

How do interleukin-1 receptor levels compare in keratoconic eyes vs normal eyes?

A

Four-fold more IL-1 receptors in keratoconic eyes

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19
Q

What does epithelial trauma result in the release of and what consequence does this have (2)?

A

Increased release of IL-1, which results in increased keratocyte loss and stromal thinning

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20
Q

What band of UV light does the cornea absorb most? What does this result in?

A

Most of the UVB light
Results in the creation of oxygen free radicals, resulting in oxidation damage

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21
Q

List three general biochemical abnormalities in keratoconus.

A

Proteinases
IL-1
Oxidative damage

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22
Q

List two environmental influences of keratoconus. What consideration may be given for this?

A

High levels of atopy including hayfever
Vigorous eye rubbing
Consider topical antihistamine or mast cell stabiliser therapy

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23
Q

In what percentage of patients is hayfever an environmental influence for keratoconus?

A

Approximately half of patients

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24
Q

What is the histopathology of the cornea in keratoconus (biochemical resistance?

A

50% decrease in biochemical resistance

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25
Q

What is the d cross linking like in keratoconic eyes?

A

A decrease in d cross links between and within collagen fibres in the anterior stroma

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26
Q

List four primary corneal changes in a keratoconic eye.

A

Epithelial anomalies
Breaks in bowmans layer
Stromal thinning
Descemets membrane breaks

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27
Q

What happens to the basal epithelial cells in keratoconic corneas (2)? What does this result in (2)?

A

Basal epithelial cells degenerate
Down-growth of epithelial basal cells into bowmans membrane
Results in a thickened basement membrane-like layer and breaks in bowmans layer occurs

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28
Q

What fills breaks in bowmans layer in a keratoconic eye?

A

Filled by eruptions of underlying stromal collagen

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29
Q

What are fleischers ring in keratoconic eyes and where can it be found?

A

Iron deposits in basal cells at the base of the cone

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30
Q

Is lamellae organisation affected in keratoconus? Explain.

A

Yes, the gross organisation changes
It is more compact and there is loss of arrangement

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31
Q

What happens to fibre bundle thickness and corneal nerve density in keratoconus?

A

Reduced density of corneal nerves and thicker fibre bundles

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32
Q

Is decemet’s membrane affected early on or late into the disease with keratoconus?

A

Late into the disease

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33
Q

What results due to breaks in descemets membrane (3)?

A

Acute corneal hydrops
Aqueaous enters the corneal stroma
Dramatic corneal oedema occurs

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34
Q

Are the symptoms of keratoconus stable or highly variable?

A

Highly variable

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35
Q

List 7 possible symptoms of keratoconus.

A

Blurred vision
Increased light sensitivity
Flaring of lights
Difficulty with night vision
Eye strain
Dry/itch/irritated eyes
History of eye rubbing

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36
Q

List 7 signs of keratoconus.

A

Reduced best corrected visual acuity
Frequent changes in refraction
Scissor reflex with retinoscopy
Charleux oil droplet with ophthalmoscopy
Doubled/distorted mires with keratometry
Corneal topography
Reduced central corneal thickness with pachymetry

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37
Q

What three things can be found with a slit lamp assessment of a keratoconic eye?

A

Vogt’s striae (corneal folds)
Fleischer’s ring
Corneal stromal thinning

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38
Q

What is corneal nerve visibility like in a keratoconic eye with slit lamp examination?

A

Increased visibility

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39
Q

Define musnon’s sign for keratoconus.

A

A V-shaped indentation observed in the lower eyelid when patient gaze is directed downwards

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40
Q

What can sometimes be seen on the apex of a keratoconic eye (2)? What is it called?

A

Superficial and/or deep opacities (apical scarring)

41
Q

Describe the four stages of keratoconus severity including the power in D and mm of curvature.

A

Stage 1 - forme fruste (sub-clinical)
Stage 2 - early - (<45D, >7.5mm)
Stage 3 - moderate (45-52D, 6.5-7.5mm)
Stage 4 - severe (>52D, <6.5mm)

42
Q

Consider forme fruste keratoconus. What is slit lamp examination and corneal topography like? What about best corrected vision?

A

Slit lamp exam normal
Minimal or no change to corneal topography over years
Best VA generally 6/6+

43
Q

What is the management for forme fruste keratoconus (2)?

A

Spectacle correction to 6/6 or 6/4.8
Soft contact lens

44
Q

What is early keratoconus primarily diagnosed by (2)?

A

Corneal topography
-central K value >47.2D
-I/S index >1.4

45
Q

What is corneal distortion like in early keratoconus (corneal topography)?

A

Minimal degree of distortion

46
Q

Is there corneal scarring in early keratoconus? What about striae or fliescher’s ring?

A

No corneal scarring
Striae and fleischer’s ring may or may not be there

47
Q

What is the management for early keratoconus (2)?

A

Spectacle acuity may be normal or mildly reduced
If normal, use spectacle/soft CL correction
If mildly reduced, use toric soft CLs or RGPs

48
Q

Is subjective refraction repeatable or poorly repeatable with keratoconus? What happens with more significant keratoconus? Explain.

A

Poorly repeatable
Multifocality of the cornea yields variable endpoint
More significant keratoconus yields higher degrees of refractive variability

49
Q

When refracting keratoconic patients, what dioptre steps may be necessary for a discernable difference? What about with JCC?

A

±1.00-3.00D
JCC ±1.00D

50
Q

List two common features of moderate/severe keratoconus.

A

Poor vision quality even with a prescription
History of progressive myopic astigmatism

51
Q

What four findings are common in a slit lamp examination of a moderate/severe keratoconic eye?

A

Striae
Fleischers ring
Prominent ectasia
Apical scarring

52
Q

What is the management for moderate/severe keratoconus (4)?

A

RGPs
Piggyback (RGP + SCL carrier)
Hybrid
Miniscleral/scleral

53
Q

List and describe the three morphologies of keratoconus and the percentage of cases for each.

A

Nipple cones - 45%
-near the corneal cenrte or inferionasal
Sagging/oval cones - 50%
-larger, below centre or inferotemporal
Globus cones - 5%
-involves up to 75% of the cornea

54
Q

Of the three morphologies for keratoconus, categorise them by their size.

A

Nipple cone - small and steep curvature
Oval cone - larger and ellipsoidal
Globus cone - largest

55
Q

Which of the three keretoconic morphologies is ideal for smaller diameter RGPs? Explain why.

A

Nipple cones
The lens will tend to centre towards the cone

56
Q

Where do oval cones tend to be steep (2)? What kind of RGP is typically required and why?

A

Inferior or inferotemporal
Small RGP will ride low, larger diameters typically required

57
Q

Which keratoconic morphology is the most challenging to fit?

A

Globus cone

58
Q

Is keratoconus an indication or contraindication for refractive surgery?

A

Contraindication

59
Q

What counsel can be given to keratoconic patients? What should management additionally involve?

A

Counsel to avoid eye rubbing
Manage co-existing or seasonal allergies with topical therapy

60
Q

What is the gold standard for monitoring keratoconic progression?

A

Corneal topography

61
Q

At what age should a child with a family history of keratoconus be assessed for keratoconus and how?

A

Perform topography early at 6-7 years of age on any child with a history of keratoconus

62
Q

In what two cases of keratoconus is a referral indicated?

A

Progressive keratoconus
Consideration for a corneal graft

63
Q

What is a treatment option for progressive early/moderate keratoconus?

A

Corneal collagen cross-linking

64
Q

What are two treatment options for end-stage keratoconus?

A

Corneal graft
-deep lamellar keratoplasty
-penetrating keratoplasty

65
Q

In what way does cross-linking occur in the eyes and where (2)?

A

Naturally with age in the cornea and lens

66
Q

List two major components of cross-linking and explain how these two interact to result in crosslinking.

A

UVA (370nm) and riboflavin
Exposure of riboflavin to UVA releases free radicals, which cause cross-linking formation between amino acids on the collagen chains

67
Q

What effect do cross-links have on collagen fibre diameter?

A

Diameter increases with cross-linking

68
Q

What happens to the space between collagen fibrils with cross-linking?

A

It increases

69
Q

Can cross-linking be done in individuals with non-progressive keratoconus?

A

No, it must be progressive and documented

70
Q

What is the minimum corneal thickness required for cross-linking?

A

400 microns

71
Q

Aside from corneal thickness, list 4 requirements for cross-linking.

A

Absence of significant corneal scarring
No history of herpetic eye disease
Not pregnant/breastfeeding
No autoimmune disorders or impaired wound healing

72
Q

List four cases a corneal graft would be considered for keratoconus.

A

Contact lens intolerance
Inability to fit a contact lens by an experienced fitter
Corneal scarring that limits acuity/quality of life
Bilaterally progressive disease with a high risk of visual impairment

73
Q

What is a serious potential side effect of laser refractive surgery? What is its clinical phenotype like?

A

Development of rpogressive corneal ectasia following surgery
Clinical phenotype essentially the same as keratoconus

74
Q

List 2 corneal topographic and 2 pathologic pre-operative risk factors for corneal ectasia following refractive surgery..

A

Abnormal pre-operative corneal topography
-asymmetric bow-tie (<1D asymmetry)
-inferior steep/skewed radial axis (I/S value <1.4)
Pathologic
-forme fruste keratoconus
-other ectasias

75
Q

List 8 general risk factors for corneal ectasia following refractive surgery.

A

Low pre-operative corneal thickness (<450 microns)
High myopia (>8.00D)
Young age
Thin residual stromal bed (<250 microns)
Family history of keratoconus
Eye rubbing
Refractive instability
BCVA <6/6

76
Q

What is the management for post-refractive surgery corneal ectasia (2)?

A

As in keratoconus, including options of cross-linking

77
Q

What is the onset of pellucid merginal degeneration, which gender does it affect more, and what is the mode of inheritance?

A

20-40s
M»F
No apparent hereditary transmission

78
Q

Which ethnicities are more affected by pellucid marginal degeneration?

A

No predilection for ethnicity

79
Q

What is pellucid merginal degeneration often misdiagnosed as?

A

Keratoconus due to similarities

80
Q

What is pellucid marginal degeneration characterised by?

A

Thinning of the corneal stroma at the peripheral inferior corneal margin

81
Q

Is pellucid marginal degeneration uni- or bilateral? Is it progressive?

A

Progressive and bilateral

82
Q

What characteristic pattern is seen on a corneal topography of pellucid marginal degeneration? What can be said of the central cornea?

A

Butterfly/crab claw
Central cornea is flatter than the peripheral cornea

83
Q

What rule of astigmatism does pellucid marginal degeneration produce and what is VA like?

A

Produces against the rule astigmatism and VA may be reasonably good

84
Q

List 3 signs of pellucid marginal degeneration.

A

Stromal thinning in a crescent band from 4-8 o’clock
No vogt striae
No fleischers ring

85
Q

Can hydrops occur in pellucid marginal degeneration?

A

Yesd but rare

86
Q

Is CL fitting more complex for keratoconus or pellucid marginal degeneration?

A

Pellucid marginal degeneration

87
Q

What is the management for pellucid marginal degeneration?

A

Similar to keratoconus, better VA is achievable

88
Q

What is the success rate of corneal grafting for pellucid marginal degeneration like compared to keratoconus?

A

Lower

89
Q

Is keratoglobus uni- or bilateral?

A

Bilateral

90
Q

Is keratoglobus inflammatory?

A

Non-inflammatory

91
Q

What is the mode of inheritance for keratoglobus?

A

Non-hereditary

92
Q

What is keratoglobus characterised by?

A

Severe thinning of the entire cornea

93
Q

What does keratoglobus lead to?

A

Gross corneal protrusion

94
Q

What four conditions is keratoglobus associated with?

A

Ehler-danlos type IV
Marfan syndrome
Leber’s congential amaurosis
Blue sclera syndrome

95
Q

What is a possible cause of keratoglobus given what conditions it is associated with?

A

Defective collagen synthesis

96
Q

List 3 signs of keratoglobus.

A

Myopic irregular astigmatism
Corneal thinning extending to the limbus
Deep anterior chamber due to corneal protrusion

97
Q

Where does maximal thinning occur with keratoglobus?

A

Midperiphery

98
Q

Are contact lenses easy to fit for keratoglobus?

A

Very difficult

99
Q

What is the prognosis for keratoglobus like with corneal grafts? Explain.

A

Poor due to thin host cornea vs donor

OD2 (S1&2) (174 decks)

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