20. Corneal Ectasia Flashcards
What is the corneal layer order (anterior to posterior)?
(6 layers)
Epithelium
Epithelial BM
Anterior limiting lamina (Bowman’s membrane)
Stroma
Posterior limiting lamina (Descemet’s membrane)
Endothelium
What is different about Bowman’s membrane compared to Descemet’s?
It’s an acellular layer composed of randomly arranged collagen fibres.
Describe the anatomy of the stroma.
A mix of ..., ..., and .../....
... tend to be equal in ... and ....
Describe the anatomy of the stroma.
A mix of collagen fibrils, keratocytes, and extracellular matrix/ground substance.
Collagen fibrils tend to be equal in diameter and distance between.
Define ‘corneal ectasia’.
Corneal conditions characterised by .... Results in ..., ..., and ....
Classified into:
1. ... e.g. ... - change over time
2. ... e.g. ... - complete ectasia of the stroma
3. ... - mechanical trauma e.g. ...
Define ‘corneal ectasia’.
Corneal conditions characterised by progressive thinning of the corneal stroma. Results in biomechanical weakening, increased corneal curvature, and irregular astigmatism.
Classified into:
1. degenerative e.g. keratoconus - change over time
2. congenital anomaly e.g. keratoglobus - complete ectasia of the stroma
3. iatrogenic ectasia - mechanical trauma e.g. post-surgery
Keratoconus - the ... primary corneal ectasia
A ..., ..., typically ... and ... ectasia of the cornea, characterised by ... of the ....
Prevalence is 1:... and affects sexes and ethnicities ..., and higher in regions where ... occurs.
Keratoconus - the most common primary corneal ectasia
A progressive, bilateral, typically asymmetric and non-inflammatory ectasia of the cornea, characterised by progressive thinning of the axial corneal stroma.
Prevalence is 1:2000 and affects sexes and ethnicities equally, and higher in regions where consanguinity occurs.
Keratoconus
Onset is typically ... and stabilises at ...-... years. Varies significantly in its ....
Associations
Most commonly an .... Possible associations with ..., ..., ..., ..., ..., and ....
Keratoconus
Onset is typically puberty and stabilises at 35-40 years. Varies significantly in its clinical course.
Associations
Most commonly an isolated ocular finding. Possible associations with atopy, Leber's congenital amaurosis, retinitis pigmentosa, Down's syndrome, connective tissue disorders, and mitral valve prolapse.
What are the three factors in the aetiology/pathogenesis of keratoconus?
- Genetics
- Biochemical abnormalities
- Environmental
Keratoconus - genetics - aetiology/pathogenesis
Classified as ... with ...; may not ... despite the gene being there.
Familial rates of keratoconus are ....
Its link with ... suggests a possible genetic abnormality with them.
Keratoconus - genetics - aetiology/pathogenesis
Classified as autosomal dominant with variable penetrance; may not always be present despite the gene being there.
Familial rates of keratoconus are uncertain.
Its link with connective tissue disorders suggests a possible genetic abnormality with them.
Keratoconus - biochemical abnormalities - aetiology/pathogenesis
Proteinases
Loss of stroma due to ... results in promotion of ....
Interleukin-1
It’s a key modulator of keratocyte ..., ..., and .... Produced by ... and .... Keratoconic corneas have ...x the amount of IL-1. Epithelial trauma causes increased release of IL-1 which results in increased ... and ....
Oxidative damage
Cornea absorbs most of the ... light which results in creation of ...; ....
Keratoconus - biochemical abnormalities - aetiology/pathogenesis
Proteinases
Loss of stroma due to protein digestion results in promotion of stromal tissue degradation.
Interleukin-1
It’s a key modulator of keratocyte proliferation, differentiation, and death. Produced by epithelium and endothelium. Keratoconic corneas have 4x the amount of IL-1. Epithelial trauma causes increased release of IL-1 which results in increased keratocyte loss and stromal thinning.
Oxidative damage
Cornea absorbs most of the UVB light which results in creation of oxygen free radicals; oxidation damage.
Keratoconus - environmental factors - aetiology/pathogenesis
High levels of ... in keratoconic patients. Vigorous ... can ... keratoconus progression.
Keratoconus - environmental factors - aetiology/pathogenesis
High levels of atopy in keratoconic patients. Vigorous eye rubbing can accelerate keratoconus progression.
Keratoconus - histopathology (1)
The cornea is ... unstable; ...% decrease in ... resistance which results in decreased ... between fibres in anterior stroma. Main changes are ..., ..., breaks in ... and ....
The ... of the epithelium degenerate. Results in downgrowth of ... into Bowman’s membrane and a .... Breaks in ... occur, filled by underlying ....
Keratoconus - histopathology (1)
The cornea is biomechanically unstable; 50% decrease in biomechanical resistance which results in decreased crosslinks between fibres in anterior stroma. Main changes are epithelial anomalies, stromal thinning, breaks in Bowman's layer and Descemet's membrane.
The basal epithelial cells of the epithelium degenerate. Results in downgrowth of basal epithelial cells into Bowman’s membrane and a thickened basement membrane-like layer. Breaks in Bowman's membrane occur, filled by underlying stromal collagen.
Keratoconus - histopathology 2
There is reduced number of ... and ... in the stroma. The organisation of the ... also becomes ... with a loss of .... There is a reduced number of ....
Descemet’s membrane remains ... until .... If there is a break, results in ...: the ... enters the corneal stroma resulting in dramatic ....
Keratoconus - histopathology 2
There is reduced number of collagen lamellae and keratocytes in the stroma. The organisation of the lamellae also becomes compacted with a loss of arrangement. There is a reduced number of corneal nerves.
Descemet’s membrane remains unaffected until late disease. If there is a break, results in acute corneal hydrops: the aqueous enters the corneal stroma resulting in dramatic corneal oedema.
What the symptoms of keratoconus?
Variable, can range from nothing to severe.
.....................
What the symptoms of keratoconus?
Variable, can range from nothing to severe.
decreased/blurred visiondecreased light sensitivitylight flaringdifficulty with night visioneye staindry/irritated/itchy eyeshistory of eye rubbing
What are the signs of keratoconus?
-
...; commonly...with.... When refracting, there are...and...is often better than expected -
...during retinoscopy -
...during ophthalmoscopy -
...during keratometry/topography -
...found by pachymetry - Vogt’s striae are
...that are found deep in the...and are...to the axis of the cone. They are produced by the...of... - (in)complete
... -
...become more visible -
...thinning -
...occurs in late stage disease -
...- can be superficial and/or deep
What are the signs of keratoconus?
-
reduced BCVA; commonlymyopicwithhigh astigmatism. When refracting, there arefrequent changesandnear acuityis often better than expected -
scissor reflexduring retinoscopy -
Charleux oil dropletduring ophthalmoscopy -
doubling/distortion of miresduring keratometry/topography -
reduced CCT, found by pachymetry - Vogt’s striae are
fine, vertical linesthat are found deep in thestromaand areparallelto the axis of the cone. They are produced by thecompressionofDescemet's membrane - (in)complete
Fleischer's ring -
corneal nervesbecome more visible -
corneal stromathinning -
Munson's signoccurs in late stage disease -
apical scarring- can be superficial and/or deep
What are the four keratoconus severity classifications?
Stage 1 - Forme fruste
Stage 2 - early
Stage 3 - moderate
Stage 4 - advanced
Stage 1 - Forme-Fruste Keratoconus
Features
* ...
* ... can look different
* Spectacle VA is ...
* Slit lamp exam is ...
* minimal or no change in ... over years
Management
* ... provides ...
* ...
Stage 1 - Forme-Fruste Keratoconus
Features
* sub-clinical form
* corneal topography can look different
* Spectacle VA is 6/6+
* Slit lamp exam is normal
* minimal or no change in corneal topography over years
Management
* spectacle correction provides normal acuity
* soft contact lenses
Stage 2 - Early Keratoconus
Features
* Diagnoses primarily by ...: central K-value > ...D and I/S index > ....
* Minimal degree of ...
* Slit lamp exam may/may not indicate ... and ...
* NO ...
Management
* Spectacle acuity may be: satisfactory, ..., and mildly reduced (...-...), ... or .../...
* If it’s a 1st time diagnosis, we must ... especially in ... patients as they have a ...
Stage 2 - Early Keratoconus
Features
* Diagnoses primarily by corneal topography: central K-value > 47.2D and I/S index > 1.4.
* Minimal degree of corneal distortion
* Slit lamp exam may/may not indicate Vogt straiae and Fleischer's ring
* NO corneal scarring
Management
* Spectacle acuity may be: satisfactory, spectacles and/or SCLs, and mildly reduced (6/6-6/9), SCL torics or RGP/hybrid lenses
* If it’s a 1st time diagnosis, we must monitor carefully especially in younger patients as they have a high risk profile
How is spectacle refraction different in keratoconus?
Subjective refraction is ..., due to ..., and worsens with .... Steps of ...-...D and JCC with ...D changes may be necessary.
Need to refract ... and must refract ....
How is spectacle refraction different in keratoconus?
Subjective refraction is poorly repeatable, due to multifocality, and worsens with later stages of keratoconus. Steps of 1-3D and JCC with 1D changes may be necessary.
Need to refract without CLs and must refract over CLs.
Stages 3-4 - Moderate and Advance Keratoconus
Features
* ... with specs and SCLs (VA of ...-...
* Typical history of ...
* Slit lamp findings: ..., ..., ..., and ...
Management
* ...
* ... CLs: ...
* ...
* ... CLs
Stages 3-4 - Moderate and Advance Keratoconus
Features
* poor vision with specs and SCLs (VA of 6/12-6/120
* Typical history of progressive myopic astigmatism
* Slit lamp findings: Vogt's straiae, Fleischer's ring, prominent ectasia, and scarring
Management
* RGPs
* piggyback CLs: RGPs with SCL carrier
* hybrid
* miniscleral/scleral CLs
What are the three morphologies of keratoconus?
- Nipple cones
- Sagging or oval cones
- Globus cones
Centred/Nipple cones
...% of cones with a ... shape; near corneal ... or ......., ...mm steepening towards central cornea.
Ideal for ... ... which tend to ... towards cone.
Centred/Nipple cones
45% of cones with a round shape; near corneal centre or inferior.Localised, 3mm steepening towards central cornea.
Ideal for smaller diameter RGPs which tend to centre towards cone.
Sagging/oval cones
...% of cones with an ... shape; ... or ... location. Larger area of steeping than ..., ...-...mm. As ... RGPs will ride low, ... diameter RGPs are required or .../... cones are required.
Sagging/oval cones
50% of cones with an ellipsoidal shape; inferior or infero-temporal location. Larger area of steeping than nipple cones, 3.0-5.5mm. As smaller RGPs will ride low, larger diameter RGPs are required or mini-scleral/hybrid cones are required.
Globus cones
...% of cones. Can involve up to ...% of the cornea. These are the ... to fit.
Globus cones
5% of cones. Can involve up to 75% of the cornea. These are the hardest to fit.
Corneal Collagen Cross-linking (CXL)
Treatment for ... keratoconus.
Uses ... on ... to release ... which cause ... between ... on collagen chains. Does not fix keratoconus. Increased ... causes increase in collagen fibre ... and ... increase the space between ....
Corneal Collagen Cross-linking (CXL)
Treatment for progressive (early/moderate) keratoconus.
Uses UVA irradiation on riboflavin to release free radicals which cause cross-linking between stromal amino acids on collagen chains. Does not fix keratoconus. Increased cross-linking causes increase in collagen fibre diameter and inter-fibre cross-links increase the space between collagen fibrils.
Which patients are appropriate for Corneal Collagen Cross-linking?
* MUST have ... keratoconus; increase >...D in apical power in ... months
* Minimum corneal thickness of ...nm
* Absence of significant ...
* No history of ...
* Not ... or ...
* No ... or ...
Which patients are appropriate for Corneal Collagen Cross-linking?
* MUST have PROGRESSIVE keratoconus; increase >1D in apical power in 12 months
* Minimum corneal thickness of 400nm
* Absence of significant corneal scarring
* No history of herpetic eye disease
* Not pregnant or breast feeding
* No autoimmune disorders or impaired wound healing
Corneal grafts
Treatment for ... keratoconus.
Which patients?
* ... to a good fit
* Inability to fit a .. by experienced fitter
* ... limits acuity and QoL
* ... with high risk of visual impairment
Corneal grafts
Treatment for end-stage keratoconus.
Which patients?
* CL intolerance to a good fit
* Inability to fit a CL by experienced fitter
* corneal scarring limits acuity and QoL
* bilaterally progressive disease with high risk of visual impairment
Corneal ectasia following refractive surgery
Serious potential side effect of laser refractive surgery. Incidence is 1:... where the aetiology is .... It can occur as early as ... week post-Sx or delayed .... Clinical phenotype is ....
Pre-operative risk factors
* Abnormal ...
o Asymmetric ... with less than ...D difference and I/S<...
* Low ..., <...nm
* ... (>...D)
* Thin residual ... (<...nm)
Management....
Corneal ectasia following refractive surgery
Serious potential side effect of laser refractive surgery. Incidence is 1:5000 where the aetiology is not entirely understood. It can occur as early as one week post-Sx or delayed several years. Clinical phenotype is basically the same as keratoconus.
Pre-operative risk factors
* Abnormal corneal topography
o Asymmetric bow-tie with less than 1D difference and I/S<1.4
* Low CCT, <450nm
* high myopes (>8.00D)
* Thin residual stromal bed (<250nm)
ManagementSame as keratoconus.
Pellucid Marginal Degeneration (1)
Onset ...-...s and more common in .... No affect by ... or .... Prevalence is ... given that it is often .... Characterised by ... at the ... with a ... (...-...mm).
Topography shows typical ... and central cornea is ... with an ... shape. It shows ... shape factor and ... the rule astigmatism.
Pellucid Marginal Degeneration (1)
Onset 20-40s and more common in males. No affect by ethnicity or hereditary transmission. Prevalence is rare given that it is often misdiagnosed as keratoconus. Characterised by progressive, bilateral thinning of the corneal stroma at the peripheral, inferior corneal margin with a narrow band above limbus (1-2mm).
Topography shows typical butterfly/crab claw and central cornea is flatter with an oblate shape. It shows negative/low shape factor and against the rule astigmatism.
What is the difference between the topography mires in keratoconus vs Pellucid Marginal Degeneration?
Keratoconus has the steepest point near centre of cornea and PMD has ghost/ghoul like appearance with tear droplet appearance.
Pellucid Marginal Degeneration (2)
Signs
Stromal thinning in a ... from ...-... o’clock positions, just above ....
Management
* Similar to keratoconus
* CL fitting is more ... as PMD has ...
* ...?
Pellucid Marginal Degeneration (2)
Signs
Stromal thinning in a narrow, crescent band from 4-8 o’clock positions, just above the limbus.
Management
* Similar to keratoconus
* CL fitting is more complex as PMD has larger coverage of degeneration
* CXL?
Keratoglobus (1)
Rare with rate 1:........
It is present at or shortly after ... but is not .... Severe thinning of the entire cornea and leads to ....
Keratoglobus (1)
Rare with rate 1:100,000.Bilateral, non-inflammatory ectasia.
It is present at or shortly after birth but is not hereditary. Severe thinning of the entire cornea and leads to gross corneal protrusion.
Keratoglobus (2)
Signs
* ...
* Corneal thinning that ... with most thinning in ...
* Normal or larger ... with ...
* ... may occur with minimal trauma due to ...
Management
* Difficult to manage ...
* Spectacles ... but will provide ...
* Requires large diameters .../.../... but are ...
* Penetrating ... has poor results due to ...
* On-lay lamellar grafts/epikeratoplasty have been used with secondary PK
Keratoglobus (2)
Signs
* myopic irregular astigmatism
* Corneal thinning that extends to the limbus with most thinning in mid-periphery
* Normal or larger corneal diameter with deep anterior chamber
* corneal perforation may occur with minimal trauma due to corneal thinness
Management
* Difficult to manage satisfactorily
* Spectacles may improve vision but will provide protection
* Requires large diameters RGPs/mini-sclerals/sclerals but are very difficult to fit
* Penetrating keratoplasty has poor results due to thin host cornea vs donor
* On-lay lamellar grafts/epikeratoplasty have been used with secondary PK
