What is a Corneal Transplant?C
Corneal transplantation is a surgical procedure used to remove a diseased or damaged cornea from a patient, and replace it with a donated piece of corneal tissue. Donor tissue come from recently deceased people who have taken the time to become a registered donor.
Donor tissue has to undergo rigorous quality assessments before being used in theatre. Donors are screened for transmissible diseases such as; HIV, Hepatitis B, Hepatitis C and Syphilis.
There are several types of corneal transplants performed, and this depends on the use of the tissue. Corneal transplants (or grafts) are generally classified as full thickness grafts (penetrating keratoplasty), anterior lamellar grafts (superficial or deep anterior lamellar keratoplasty), posterior lamellar grafts (Descemet’s stripping endothelial keratoplasty (DSEK), or Descemet’s membrane endothelial keratoplasty (DMEK)).
Keratoconus causes a thin ectatic cornea in younger patients and Fuch’s corneal endothelial dystrophy causes a thickened cornea in older patients. Both result in worsening vision with disease progression. Together these two diagnoses consistently represent the underlying diagnosis in 80-90% of all corneal transplants performed.
Indications for transplantation include:
- To improve the vision
- Contact lens intolerance
- To relieve pain
- To plug a hole in the eye (Tectonic)
- To reduce or eliminate the bulk of an infected cornea
Full thickness (Penetrating Keratoplasty) Corneal Transplant
In a full thickness corneal transplant; the corneal epithelium, stroma and endothelium are all replaced in one circular button. The transplant is oversized to ensure it will be suitable fit for the patient.
Deep anterior Lamellar Keratoplasty (DALK)
The internal lining of the cornea is a monolayer of cells (corneal endothelium) that sits on a Descemet’s membrane. In a maximal depth DALK transplant, this layer is stripped from the other layers. This transplant is best suited for Keratoconus patients with no stromal scarring already or previous hydrops events.
Posterior lamellar Corneal Transplants
This type of transplant is where the corneal endothelium is transplanted on its basement membrane (Descemet’s) in the patient’s eye. Descemet’s stripping endothelial keratoplasty (DSEK) are typically 150-200 um thick and contain corneal stroma from the donor cornea in addition to Dsecemet’s memebrane and the endothelial cell mosaic. Descemet’s membrane endothelial keraoplasty (DMEK) is 10-15um thick and contains no residual donor cornea stroma.
Posterior lamellar corneal grafts are transplants offered to patients with Fuch’s Dystrophy or Pseudophakic Bullous Keratopathy. Replacing the internal layer of cells still leaves the recipient’s cornea intact, but removes the diseased endothelium layer. DLEK is a defunct forerunner of modern posterior lamellar graft procedures with poorer visual outcomes due to marked interface haze.
A full thickness corneal transplant all patients with no other eye disease has the capability of improving the corrected vision to within driving limits but only 60% achieve this in spectacles. Full thickness transplants have a low primary graft failure rate (<1%) . 87% of DSEK patients without any other significant eye disease can expect to be corrected to within driving limits within 3 months of surgery while the primary failure rate is less than 3%. All patients undergoing a DMEK procedure with no other eye disease can expect to see within driving limits and 80% of successful DMEKS can be corrected to 20/20 level of vision. However in Queensland the DMEK procedure is associated with a 33% primary graft failure necessitating very early regraft.
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