Prof. Michael Mimouni completed his fellowship at Canada’s leading center for corneal transplantation. During this period he trained in and mastered all types of corneal transplant procedures, including full-thickness corneal transplantation (PKP), anterior lamellar transplantation (DALK), and partial-thickness posterior grafts (DSAEK and DMEK). He also gained experience with advanced grafts such as the Boston KPro and with Descemet stripping without a corneal graft (DSO).
What is a corneal transplant?
A corneal transplant is a surgical procedure in which a damaged or diseased cornea is replaced with donated corneal tissue (the graft). The graft is taken from a recently deceased person with no known diseases or other factors that could affect the survival of the donated tissue or the health of the recipient.
In the image to your left you can see the common types of corneal transplants (PKP, DALK, DSAEK, and DMEK), where red represents the donor cornea and black represents the recipient’s cornea.
Full-thickness corneal transplantation (PKP)
Full-thickness corneal transplantation (known as PKP, short for Penetrating Keratoplasty) is performed when all layers of the cornea are damaged and neither an anterior nor a posterior lamellar graft is possible. A full-thickness corneal graft may be secured with continuous sutures or single (interrupted) sutures. This type of graft has a longer recovery period, and we wait about 8-12 months before beginning to remove the sutures, in order to allow the tissue to heal and integrate properly.
In the image to your left is an example of a full-thickness corneal graft with 16 interrupted sutures. You can also see that a special ring called a Goldman Ring was used to maintain the tectonic strength of the cornea throughout the surgery and prevent complications.
Deep anterior lamellar keratoplasty (DALK)
Deep anterior lamellar keratoplasty (known as DALK) is performed when the anterior layers of the cornea are damaged (for example, in keratoconus) but the corneal endothelium is healthy. The advantage of this graft is that the patient’s own natural endothelial cells are preserved. This graft can also be secured with interrupted or continuous sutures. Recovery from this type of graft is somewhat faster than from a full-thickness graft, and suture removal can begin slightly earlier.
In the image to your left is an example of a DALK graft at the stage of injecting a large air bubble (Anwar’s Big Bubble Technique). This technique yields better results than manual dissection. Here, too, a Goldman Ring is used to maintain tectonic strength.
Partial-thickness posterior corneal transplantation: DMEK
DMEK stands for Descemet Membrane Endothelial Keratoplasty. It is performed when the anterior layers of the cornea are healthy but the corneal endothelium is damaged or not functioning (for example, corneal decompensation after cataract surgery or in Fuchs dystrophy). The advantage of this graft is that only the thin damaged layer is replaced: these grafts are less than 20 microns thick (the entire cornea is about 550 microns), meaning that less than 5% of the corneal thickness is replaced. This type of graft sometimes requires one or two sutures (sometimes none at all). When the surgery is successful, recovery takes a few weeks. This graft carries a lower risk of graft rejection than a full-thickness graft. In 10-20% of cases, an additional air bubble needs to be injected in the first weeks after surgery.
In the image to your left is an example of a DMEK graft. The anterior chamber of the eye is filled with air in order to press the thin graft against the patient’s cornea. You can see the letter F marked with a dot to its lower right. This marking allows the surgeon to confirm that the graft is not upside down, and it fades within a few days.
Partial-thickness posterior corneal transplantation: DSAEK
DSAEK stands for Descemet Stripping Automated Endothelial Keratoplasty. It is performed when the anterior layers of the cornea are healthy but the corneal endothelium is damaged or not functioning, and DMEK is either not feasible or would be very complex (poor visibility, long eyes, eyes after vitrectomy, and more). In this type of transplant, the endothelial tissue is replaced with endothelial tissue together with a small amount of stroma (corneal tissue), so the graft thickness ranges from 60 to 150 microns (depending on the cutting capability of the microkeratome). This graft requires a few interrupted sutures, which can be removed as early as one month after surgery. When the surgery is successful, recovery takes a few months. This graft carries a lower risk of rejection than a full-thickness graft, but a higher risk than a DMEK graft. As with DMEK, additional air may need to be injected into the anterior chamber after surgery, though this is less likely than with DMEK.
In the image to your left is an example of a DSAEK graft. Here, too, the anterior chamber of the eye is filled with air in order to press the DSAEK graft against the patient’s cornea.