AED - Corneal Ectasia - Week 11 Flashcards by Davud Akgun

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

It is not

It is an acellular layer composed of randomly arranged collagen fibres

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How thicc is the corneal stroma typically?

500μm

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

Corneal conditions that are characterised by progressive thinning of the corneal stroma

biochemical weakening
increased corneal curvature
irregular astigmatism

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

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

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

Progressive, typically asymmetrical, and non-inflammatory

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

Progressive thinning of the axial corneal stroma

It is bilateral

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What condition is the most common primary corneal ectasia?

Keratoconus

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In what regions is the prevalence of keratoconus higher?

Regions where cosanguinity occurs

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

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

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

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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What is the aetiology and pathogenesis of keratoconus?

Uncertain

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

Autosomal dominant with variable penetrance

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

A possible genetic abnormality in connective tissues

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What do family members of a keratoconic individual typically have?

30-50% have subtle topographic abnormalities

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Explain two biochemical abnormalities of proteinases in keratoconus.

Increased proteinase activity

Decreased activity of proteinase inhibitors

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How does interleukin-1 affect keratocytes (3)?

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

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

Epithelium and endothelium

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

Four-fold more IL-1 receptors in keratoconic eyes

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

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

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

Most of the UVB light

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

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List three general biochemical abnormalities in keratoconus.

Proteinases
IL-1
Oxidative damage

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

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

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

Approximately half of patients

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

50% decrease in biochemical resistance

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What is the d cross linking like in keratoconic eyes?

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

List four primary corneal changes in a keratoconic eye.

Epithelial anomalies Breaks in bowmans layer Stromal thinning Descemets membrane breaks

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

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

What fills breaks in bowmans layer in a keratoconic eye?

Filled by eruptions of underlying stromal collagen

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

Iron deposits in basal cells at the base of the cone

Is lamellae organisation affected in keratoconus? Explain.

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

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

Reduced density of corneal nerves and thicker fibre bundles

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

Late into the disease

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

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

Are the symptoms of keratoconus stable or highly variable?

Highly variable

List 7 possible symptoms of keratoconus.

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

List 7 signs of keratoconus.

``` 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 ```

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

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

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

Increased visibility

Define musnon's sign for keratoconus.

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

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

Superficial and/or deep opacities (apical scarring)

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

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)

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

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

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

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

What is early keratoconus primarily diagnosed by (2)?

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

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

Minimal degree of distortion

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

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

What is the management for early keratoconus (2)?

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

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

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

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

±1.00-3.00D | JCC ±1.00D

List two common features of moderate/severe keratoconus.

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

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

Striae Fleischers ring Prominent ectasia Apical scarring

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

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

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

``` 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 ```

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

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

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

Nipple cones | The lens will tend to centre towards the cone

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

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

Which keratoconic morphology is the most challenging to fit?

Globus cone

Is keratoconus an indication or contraindication for refractive surgery?

Contraindication

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

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

What is the gold standard for monitoring keratoconic progression?

Corneal topography

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

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

In what two cases of keratoconus is a referral indicated?

Progressive keratoconus | Consideration for a corneal graft

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

Corneal collagen cross-linking

What are two treatment options for end-stage keratoconus?

Corneal graft - deep lamellar keratoplasty - penetrating keratoplasty

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

Naturally with age in the cornea and lens

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

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

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

Diameter increases with cross-linking

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

It increases

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

No, it must be progressive and documented

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

400 microns

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

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

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

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

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

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

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

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

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

``` 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 ```

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

As in keratoconus, including options of cross-linking

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

20-40s M>>F No apparent hereditary transmission

Which ethnicities are more affected by pellucid marginal degeneration?

No predilection for ethnicity

What is pellucid merginal degeneration often misdiagnosed as?

Keratoconus due to similarities

What is pellucid marginal degeneration characterised by?

Thinning of the corneal stroma at the peripheral inferior corneal margin

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

Progressive and bilateral

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

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

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

Produces against the rule astigmatism and VA may be reasonably good

List 3 signs of pellucid marginal degeneration.

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

Can hydrops occur in pellucid marginal degeneration?

Yesd but rare

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

Pellucid marginal degeneration

What is the management for pellucid marginal degeneration?

Similar to keratoconus, better VA is achievable

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

Lower

Is keratoglobus uni- or bilateral?

Bilateral

Is keratoglobus inflammatory?

Non-inflammatory

What is the mode of inheritance for keratoglobus?

Non-hereditary

What is keratoglobus characterised by?

Severe thinning of the entire cornea

What does keratoglobus lead to?

Gross corneal protrusion

What four conditions is keratoglobus associated with?

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

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

Defective collagen synthesis

List 3 signs of keratoglobus.

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

Where does maximal thinning occur with keratoglobus?

Midperiphery

Are contact lenses easy to fit for keratoglobus?

Very difficult

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

Poor due to thin host cornea vs donor