The cornea is the clear window at the front of the eye and is responsible for over 75% of the focusing power of the eye. Thus any damage or disease of the cornea can dramatically affect vision.
The cornea consists of 5 layers. Modern day corneal transplants can not only transplant the entire cornea (called a penetrating keratoplasty, or full-thickness transplant), but can transplant specific layers of the cornea (called lamellar keratoplasty or partial thickness transplants) to specifically target the damaged layer of the cornea.
Full Thickness Corneal Transplants
Penetrating Keratoplasty (PKP)
This is a tried and tested technique for corneal transplantation and has been used for over 40 years. It involves using a circular trephine to cut a full-thickness hole in the cornea and stitching a new full thickness corneal graft in its place. The stitches remain in place for about 1 year while the cornea is healing and drops are used to prevent corneal rejection during this time. This technique is ideal for patients who have damage to all layers of the cornea.
Partial Thickness (Lamellar) Corneal Transplants
There are two main types of lamellar transplants depending on which part of the cornea is replaced. In endothelial keratoplasties (of which Descemet’s membrane endothelial keratoplasty or DMEK is the newest version) the inner layers are transplanted while in deep anterior lamellar keratoplasty the outer layers are transplanted.
Descemet’s Membrane Endothelial Keratoplasty (DMEK)
This is the transplant of the inner layers of the cornea. The newest version of the transplant (DMEK) involves the transplantation of just the inner two layers of the cornea (Descemet’s membrane and endothelial cells) and is used to treat diseases that affect the endothelium such as Fuchs’ Endothelial Corneal Dystrophy or bullous keratopathy. This technique generally has better visual outcomes, faster recovery and lower long-term rejection rates than older techniques such as DSAEK. It is a keyhole type surgery where the graft is folded and injected into the eye through a 2.4mm incision before being unfolded, positioned and held in place within the eye with an air bubble. The eye will absorb the air bubble within a few days.
Deep Anterior Lamellar Keratoplasty (DALK)
This is the transplant of the outer three layers of the cornea leaving only the Descemet’s membrane and endothelium. It is primarily used to treat diseases of stroma such as corneal scars, and advanced keratoconus. Here an air bubble is used to separate the stroma from Descemet’s membrane and carefully removed. The transplant is then stitched in place to replace the removed tissue. The stitches remain for about 9-12 months and drops are used during this time. The major advantage of this technique over a PKP is lower rejection rates (as endothelium is not transplanted) and a faster recovery time.
Structure of the Cornea
Common Corneal Conditions