7 - Corneal dystrophies Flashcards
Where does the word dystrophy originate from?
Greek:
- dys = wrong, difficult
- trophy = nourishment
What is corneal dystrophy classification based on?
some based on anatomical corneal layer affected, other based on aetiology
What are the layers that make up the cornea? (from most superficial)
- Epithelium, made of 10 layers
- Bowman’s membrane
- Stroma
- Descemet’s membrane
- Endothelium
What is the function of the endothelium in the cornea?
extracting excess water & other liquids from the stroma, without it –> stroma would become oedematous
In corneal dystrophies, what are the 2 main impacts on visual acuity?
- reduction of transparency
2. induction of H.O.A (high order aberration)
What is a H.O.A (higher order aberration)?
- minor imperfections on corneal surface
= when the surface of lens is irregular –> many focal points are found on the focal plane
it may be caused by: scar tissue, traumatic injury, disease, complications from surgery,
- can’t be corrected w/ glasses, but can be w/ contact lenses –> acts as an artificial lens which is extremely regular –> no aberration, light rays land on single focal point
What is a L.O.A (lower order aberrations)?
AKA refractive errors
- myopia (nearsightedness)
- hyperopia (farsightedness)
- astigmatism
- “pistons”
Astigmatism = ?
general blurriness of vision caused by uneven cornea shape. It often accompanies nearsightedness and farsightedness.
Hyperopia = ?
Farsightedness –> distant objects can be seen clearly but objects that are nearby appear out of focus. Caused by light focusing behind the retina.
Myopia = ?
Nearsightedness –> nearby objects can be seen clearly but objects that are far away appear out of focus. Caused by light focusing short of the retina.
What do large peripheral depositions induce?
What do small areas of deposition induce?
large depositions –> Flattening of the cornea
small areas of depositions –> Steeping “ “
Which technique is used to map the corneal curvature, how is it interpreted?
TOPOGRAPHY – diff colors are associated w/ diff degrees of curvature
in case of flattening –> a cold color is used
blue = v flat red = v steep
green/yellow = normal corneal curvature
(OCT is also useful –> shows areas of thickening & steepening of pathological corneal tissue)
Which is more important – opacity or irregularity?
- irregularities
- an opacity is often compatible w/ good visual acuity, a slight irregularity isn’t –> if shape of cornea is irregular –> visual acuity is affected
What are the 6 epithelial & subepithelial dystrophies?
- Epithelial basement membrane dystrophy (EBMD)
- Epithelial recurrent erosion “ (ERED)
- Subepithelial mucinous corneal “/CD (SMCD)
- Meesmann CD (MECD) (Mutation in keratin genes)
- Lisch epithelial CD (LECD)
- Gelatinous drop-like CD
What are the 3 Bowman’s layer dystrophies?
- Reis-Buckler’s CD (RBCD) aka Granular CD type 3 (1 of most common)
- Thiel-Behnke CD (TBCD)
- Grayson-Wilbrandt CD (GWCD)
What are the 8 main stromal dystrophies?
- Lattice CDs
- Granular CDs
- Macular CD (MCD)
- Schnyder CDs (SCD)
- Congenital stromal CD (CSCD)
- Posterior amorphous CD (PACD)
- Central cloudy dystrophy of Francis (CCDF)
- Pre-Descemet CD (PDCD)
What are the 4 main Descemet membrane & endothelial dystrophies?
- Fuchs endothelial CD ( FECD)
- Posterior polymorphous CD (PPCD)
- Congenital hereditary endothelial dystrophy (CHED)
- X-linked endothelial CD (XECD)
What is keratoconus? (KC, KCN, KTCN)
- eye disorder ==> results in progressive corneal thinning
- stroma becomes mechanically weaker
- since cornea is thinner + weaker –> becomes steeper & space b/w cornea & iris gets larger
- usually bilateral
What is characteristic of a keratoconus cornea?
easily bends compared to a normal one
Clinical manifestations of keratoconus
- blurry vision
- double vision
- nearsightedness
- astigmatism
- light sensitivity
- late stages –> apex of cornea becomes cloudy & visual acuity decreases
usually bilateral
severe cases –> scarring or a circle seen within cornea
What are the causes & prevalence of keratoconus?
prevalence: 1 in 2000
causes: unknown, combo of genetic, environmental & hormonal factors
7% affected have fam history
environmental –> rubbing eyes + allergies
What are the main features of Reis-Buckler’s CD?
- autosomal dominant
- onset: childhood
- gene: TGFBI locus 5q31
- confluent irregular & coarse geographic-like opacities w/ varying densities (at Bowman layer & superficial stroma)
- initially separated from one another
- opacities may later extend to limbus & deeper stroma
What are the changes to Bowman’s layer in Reis-Buckler’s CD?
- whitish net develops on Bowman layer –> is replaced by sheet-like layer of granular Masson trichrome-red deposits –> can extend to subepithelial stroma
- in advanced –> sparse round deposits in middle & posterior stroma
How is Reis-Buckler’s CD treated?
- if diagnosis is early –> peeling off pathological tissue
- if done correctly –> recurrence only 20yr later
- if late diagnosis –> Bowman layers already strongly attached to stroma –> peeling is hard + require lasers –> excimer ablation, SALK or DALK
What instrument is used in the treatment of Reis-Buckler’s CD?
Vinciguerra spatula
Why is an early diagnosis of Reis-Buckler’s CD important ?
crucial for the disease outcome, as with time the opacities can extend
from the Bowman layer to the deep stroma (can peel off layer If diagnosed early)
Why is peeling better than transplantation in Reis-Buckler’s CD?
- no risk of rejection
- lower risk of recurrence
- in transplant –> area of cornea excised is limited, w/ peeling –> remove entire layer –> no risk of leaving some dystrophic tissue
remnants of dystrophic tissue can regrow –> recurrence
What are the main features of epithelial basement membrane dystrophy (Cogan dx)?
- aka map-dot-fingerprint
- affects anterior cornea
- characteristics slit lamp findings –> may result in decr vision &/or recurrent corneal erosions
Explain why epithelial basement membrane dystrophy (Cogan dx) is known as “map-dot-fingerprint & how this dystrophy develops.
the pattern of deposits resembles a fingerprint –> areas where deposits are v thick & others where they barely exist
- extra sheets of BM extend into corneal epithelium (“maps”)
- maturing epithelial cells migrating to ant surf of epith get entrapped in these sheets –> forming cysts (“dots”)
- parallel lines of thickened BM present as “fingerprints”
causes BLURRED VISION
BM abnormalities may interfere w/ adherence of epithelial cells to BM –> painful, recurrent corneal lesions
Diagnosis & treatment of epithelial basement membrane dystrophy (Cogan dx)
layering of deposits is seen at OCT
in late stages –> peeling impossible –> must use lasers
What are the main features of central cloudy dystrophy of Francois?
- v rare form of anterior stromal corneal dystrophy
- polygonal or rounded stromal opacities surrounded by clear tissue
- no effect on vision
- lesions appear in 1st decade of life
- most asymp
- non-progressive dx course
What are the main features of Crystalline (Schnyder) CD?
- rare form of stromal CD
- corneal clouding or crystals in corneal stroma
- progressive decrease in visual acuity
- early stage –> crystals appear, small decr in visual acuity
- then –> coalescence of crystals in 1 layer of crystals –> v thick + opaque –> affects shape & regularity of cornea –> visual acuity totally lost
How is Crystalline (Schnyder) CD treated?
Excimer laser –> selectively ablates pathological tissue
What are the main features of Granular (Groenouw) dystrophy?
- most common dystrophy
- 2 forms:
1. Type I
2. Type II
Type I granular dystrophy (GCDI) = rare form of stromal corneal dystrophy
- multiple small deposits in superficial central corneal stroma
- progressive visual impairment
- autosomal dominant
- perfect transparency, no opacities
Type II
- opacities in b.w the deposits
Treatment of Granular (Groenouw) dystrophy.
early stages w/ opacities –> Excimer laser –> restores regularity of cornea & thus visual acuity
dx may progress & transparency b/w deposits progressively decreases
later stages –> DALK
What is the main difference b/w type I & type II Granular (Groenouw) dystrophy ?
Type II shows opacities in between the
deposits, while the Type I has a perfect transparency.
What are the main features of lattice CD?
- autosomal dominant
- appears in 1st decade of life
- thin branching refractive lines (lattice lines) &/or subepithelial, whitish, ovoid dots
- involved anterior stroma
Treatment of lattice CD
best option = Excimer laser –> selectively remove damaged opaque layer –> restore visual acuity
but still frequently treated w/ PK
What are the main features of Salzmann dystrophy?
- new tissue is deposited on surf
- may be genetic, but usually induced by chronic inflammation of eye
- cornea highly irregular
- Salzmann’s nodular degeneration (SND)
> slowly progressive, grey-white to bluish nodules (1-3mm) anterior to Bowman’s layer
> usually bilateral
How does Salzmann’s nodular degeneration (SND) develop?
Enzymatic destroy of Bowman’s layer –> migration & proliferation of keratocytes from posterior stroma –> secondary deposition of ECM components in nodular areas
Treatment of Salzmann dystrophy
- easily peel off layer w. Vinciguerra spatula
- after 2-3days –> epithelium reforms –> completely transparent + regular
corneal transplant –> sometimes, but peeling & laser if possible
grafts –> high risk of having residual pathological tissue in periphery
Patients who have been poorly surgically treated could develop Salzmann’s dystrophy over time. True or false?
Facts.
Ca deposits are found in some dystrophies, what is the treatment of Ca deposits in the cornea?
- corneal grafting (not right solution)
- trephination (surgery –> hole is drilled) - hard, cornea may end up irregular –> refractory defects
- peeling w/ spatula & excimer laser –> enough to restore vision once deposits removed (cornea remains intact)
- laser produces vibrations via microshock waves –> help peeling by separating patho tissue from normal
- Vinciguerra spatula –> to redistribute the fluid & obtain fully transparent cornea & regular shape
What are the main features of a penetrating keratectomy?
- aka corneal transplant/graft
- surgical removal of damaged or diseased part of cornea –> then implantation of healthy tissue from donator
- latest method = substitute only stroma, leave endothelium untouched –> air injected inside cornea –> separating endothelium from stroma
What are the main features of a superficial anterior lamellar keratectomy (SALK)?
- selective incision of corneal epithelium & stroma –> so endothelium & part of deep stroma are left
- lamella excised is v thin
- not very effective
What are the main features of a Sequential Custom Therapeutical Keratectomy (SCTK)?
- used in early stages of CDs & keratoconus
- aka Excimer ablation
- laser transforms corneal tissue into gas
- heating avoided –> occurs at cold temp
- non-invasive, takes microsec, totally painless
- in later stages of dx –> cornea is mapped –> remove more tissue where required
- becoming new first line approach
- if not effective –> can just do graft
What are the main features of a Deep Anterior Lamellar Keratoplasty (DALK)?0
- removal of corneal stroma down to Descemet’s membrane
- most useful for corneal dx w normal endothelium
What are the main features of a Deep Anterior Lamellar Keratoplasty (DALK)?0
- removal of corneal stroma down to Descemet’s membrane
- most useful for corneal dx w normal endothelium
Penetrating Keratopkasty (PK) vs DALK, which is preferred & why?
- DALK is preferred
Why?
- traditionally, penetrating keratoplasty (PK or “full-thickness”) –> full-thickness corneal graft was treatm for corneal stromal diseases
BUT can be complicated (by graft rejection, neovessel formation, irregular astigmatism, corneal opacification –> visual impairment)
- DALK instead may lessen those risks –> recipient’s Descemet’s membr & endothelium are preserved
What are the steps in performing a DALK?
- Mark host cornea to obtain reference line for radial scission & plan host trephination
- Trephine the host cornea. Depth of cut can be adjusted –> usually don’t cut full thickness
- Spatula inserted to identify deepest later for corneal dissetcion
- Air injected (via needle) to separate endothelium from stroma
- Debulk anterior stroma
- Mark stroma w/ dye
- Cover mark w/ viscous solution + make incision thru mark (viscous sol prevents rapid escape of injected air)
- Inject viscous sol thru incision into space b/w posterior stroma & endothelium –> complete the separation (of the 2 layers) w/ forceps –> cut away pathological stromal tissue (endothelium is preserved)
- Suture donor tissue to host corneal tissue
Corneal transplantation is considered the last treatment option in patients with corneal dystrophies/CDs. True or false?
facts
How can one evaluate the severity of dystrophies?
- Keratoscopy - poor corneal reflex means severe condition
- Curvature map (tangential map)
done at pre-operative stage to assess severity
repeated at intra-operative stage too
(continuous monitoring to be sure)
Are there more or less new vessels in corneal dystrophies?
MORE
- excessive growth of tissue –> result = thicker layer & tear layer is not
enough to feed the tissue –> new vessels grow on cornea to supply it. - treat the cornea & regularise it w/ peeling and laser –> restoration of the normal thickness of epithelium (60μm) and the pachymetry map –> vessels disappear over time and cornea restores its transparency –> bc no more leakage of plasma from vessels (edema)
