CLM - Irregular Cornea Fitting I - Week 7 Flashcards
What is a keratoplasty?
Corneal transplant/graft
What is the oldest form of human transplantation?
Blood transfusion, followed by keratoplasty
Is everyone a universal donor for keratoplasty? Is blood typing required? Does donor age have an impact?
Yes
No blood typing required
Donor age not as important as other tissue transplants
What age are most donor eyes?
> 60
Do grafts from donors <50 have better survival raves vs >60?
Yes, significantly
What diseases need to be excluded from corneal donors (4)?
Severe infections
Haematological malignancies
HIV
Hepatitis
What is the longevity of a corneal graft? Explain.
Up to 150 years, exact number unknown
If most grafts come from donors aged 60+, most grafts will be very old
What is the waiting time for a corneal graft?
6-9 months
How soon is the cornea removed from a donor eye?
Within hours of death
What is a penetrating keratoplasty? List all the layers of the cornea involved (5).
Full thickness graft
-epithelium
-bowman’s layer
-stroma
-descemet’s membrane
-endothelium
What is a deep anterior lamellar keratoplasty? List all the layers of the cornea involved (3).
A partial thickness graft
-epithelium
-bowman’s membrane
-stroma
What is a descemet’s stripping automated endothelial keratoplasty? List all the layers of the cornea involved (3). Describe how the graft tissue is prepared.
A partial thickness graft
-stroma
-descemet’s membrane
-endothelium
Tissue is prepared using an automated microkeratome
What is a descemet’s membrane endothelial keratoplasty? List all the layers of the cornea (2).
Partial thickness graft
-descemet’s membrane
-endothelium
Compare the rates of full thickness, DALK, DSAEK, and DMEK procedures over recent times.
Full thickness rates are decreasing, while the others are increasing, notably DSAEK and DMEK
Do all partial thiccness keratoplasties preserve descemet’s membrane and endothelium?
Yes
How does retaining descemet’s membrane affect the post-graft cornea?
Increases structural integrity
Where do most corneal graft rejections occur? Retaining what layer will minimise the risk of rejection?
Uusally begins in the endothelium
Retaining the endothelium reduces the chance of rejection
What anaesthesia is used for corneal graft procedures (technique not drug)?
General or retrobulbar with IV sedation
Majority done under local anaesthesia
What is the graft size determined by (2)?
Size of the recipient cornea
Area of the disease
Does the risk of rejection increase or decrease with increasing graft size?
Increases
How wide are full thickness corneal grafts in diameter typically?
7.5-8.5mm
What instrument is used to excise the host cornea and what does it look like? What is used to maintain stability?
A trephine - an instrument with a circular blade that suctions onto the cornea
When twisted, the blade slices the cornea
The rest is incised manually
Vacuum is used to maintain suction and stability
What risks are presented if the graft size is >8.5mm, aside from increased rejection risk (3)?
Post-op increase in IOP
Anterior synaechiae
Vascularisation
What risk is presented if the graft size is >7.0mm?
Smaller sizes give rise to higher astigmatism due to increased tension from the host
How is the graft centred (2)?
It is centred over the pupil and displaced slightly nasally
For the host cornea, briefly describe how layers are separated in deep anterior lamellar keratoplasty (3).
Trephine used to incise cornea 2/3rds
Air bubble injected
Viscoelastic injected between descemet’s membrane and the stroma
For the donor graft, briefly describe how layers are separated in deep anterior lamellar keratoplasty (2).
Descemet’s membrane is stained with tryptophan blue
It is then manually removed
Compare visual outcomes in deep anterior lamellar keratoplasty vs penetrating keratoplasty. Explain why they are so.
Penetrating keratoplasty can often achieve 6/6= vision
Due to the extra interface, final best VA for DALK is often reduced a line
Is deep anterior lamellar keratoplasty easier or more challenging to carry out?
More challenging
What are the three most common diseases treated by penetrating keratoplasty (in order)?
Keratoconus
Failed previous graft
Bullous keratopathy
What are the two most common diseases treated by partial thickness keratoplasties?
Fuch’s endothelial corneal dystrophy
Bullous keratopathy
Corneal grafts performed for which disease has significantly better graft survival vs other indications?
Keratoconus
Post graft surgery, how long does it take for complete corneal epithelial healing? what is this important for?
94% in 7 days
-important to re-establish barrier to infection
What is the normal endothelial count in a 20 year old vs 80? what may happen if the count reaches 500-1000?
2,800 cells/mm2 - 20 year old
2,500 to 2,000 cells/mm2 - 80 year old
Corneal decompensation may occur at low counts
Are endothelial cells lost at the graft-host junction after graft surgery? What is the rate of endothelial cell loss like after surgery?
Cells lost at the junction
Ongoing endothelial cell loss still occurs
Is endothelial cell loss more rapid in the graft or the host cornea following graft surgery?
More rapid in the graft
Following graft surgery, when does majority of endothelial cell loss occur?
Within the first two years
How does endothelial cell loss compare in penetrating keratoplasty vs DALK?
Significantly less endothelial loss due to retention of host endothelium
Where is corneal sensitivity maximal?
At the corneal apex
What happens to corneal nerves in penetrating keratoplasty and DALK? What is corneal sensitivity like post surgery?
They are severed
Central grafts are completely or markedly hypo-aesthetic
Compare corneal sensitivity after a penetrating keratoplasty vs DALK.
More sensitivity in DALK vs PK
List four complications following graft surgery.
Flat anterior chamber
Acute post-operative glaucoma
Persistent epithelial defects
Infection
Describe a fixed dilated pupil following graft surgery and how it can occur (2).
Due to ischameic atrophy of the iris sphincter secondary to an iris strangulation
List three ways glaucoma can occur after graft surgery.
Chronic secondary (anterior synaechiae)
Steroid induced
Secondary inflammatory (uveitis)
Can cataracts occur after graft surgery?
Yes, posterior subcapsular from steroid
List three optical complications after graft surgery.
High degree of regular astigmatism
Irregular astigmatism
Significant anisometropia
What is vision like immediately after graft surgery and why? What happens over the next few weeks?
Hazy due to folds in descemet’s membrane
Gradually improves over weeks and months as graft endothelium clears graft stromal oedema
Is it possible to predict the quality of vision following graft surgery?
Not
What can be done to reduce excessive astigmatism (2)?
Monitor it using topography and selectively remove/insert sutures
What is vision often like with sutures in and once they are removed? Explain why.
Patients may achieve good quality vision with sutures in as they maintain regular curvature
Once removed, stresses within the graft can influence host toricity
-vision may deteriorate
Is vision likely to improve followjng suture removal?
No
If there is significant myopia, regular and/or irregular astigmatism, will they be compensated for by the removal of the sutures?
No
Compare VA outcomes in full thickness vs DALK grafts (percentages).
Full thickness grafts for keratoconus - 75% achieve a post graft VA of 6/12
DALK - 50% achieve a post graft VA of 6/12
What percentage of graft recipients have regular astigmatism (and what magnitude)? Is there a difference in rates between full/partial thickness grafts?
Up to 50% had regular astigmatism of >5.00D
-no difference between full/partial thickness grafts
Is topography useful for information on elevation of the peripheral host cornea?
No, limited information
What are the four components of graft assessment?
Topography maps
Corneal toricity - regular/irregular astigmatism
Graft diameter - measure it
Location of the graft - displaced from the corneal centre
What can cause scarring/haze after graft surgery (6)?
Generalised scarring
Suture scars
Overall haze due to aged graft
Peripheral haze due to arcus
Rejection episodes
Herpes scars
What is meant by blood vessel ingrowth?
Blood vessel growth to the graft - a pathway for inflammation
What should be noted when assessing active blood vessel ingrowth (5)?
Size
Number
Location
Extent within the host
Extent within the graft
How does inactive blood vessel ingrowth appear and what is a technique to see them?
Ghost vessels - retro-illumination
What is the most significant factor in determining graft failure?
Corneal vascularisation
Consider graft surgery to treat keratoconus. Can the host cornea continue to thin (2)? Explain what can happen after (2).
It can continue to develop
-take particular note from 4 to 8 o’clock
If the host cornea thins too much, it can cause sagging and an inferior bulging of the graft
Is refractive keratoplasty done while sutures are still in place or once they are removed?
Typically wait until all sutures are out before doing refractive keratoplasty
What is refractive keratoplasty?
Insertion of sutures to reduce corneal astigmatism
