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 4
x 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 vision
decreased light sensitivity
light flaring
difficulty with night vision
eye stain
dry/irritated/itchy eyes
history 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
; commonlymyopic
withhigh astigmatism
. When refracting, there arefrequent changes
andnear acuity
is often better than expected -
scissor reflex
during retinoscopy -
Charleux oil droplet
during ophthalmoscopy -
doubling/distortion of mires
during keratometry/topography -
reduced CCT
, found by pachymetry - Vogt’s striae are
fine, vertical lines
that are found deep in thestroma
and areparallel
to the axis of the cone. They are produced by thecompression
ofDescemet's membrane
- (in)complete
Fleischer's ring
-
corneal nerves
become more visible -
corneal stroma
thinning -
Munson's sign
occurs 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