Lamellar Keratoplasty (LK) of Partial Thickness Cornea Transplant
If the cornea has become cloudy and the damage is limited to the front or back of the cornea, a lamellar keratoplasty (LK) or partial thickness transplant may be the best option. Remember that the cornea is composed of five layers. The image below depicts the layers from front to back: endothelium, Bowman’s membrane, stroma, Descemet’s membrane, and endothelium.
Posterior Lamellar Corneal Transplants
The back surface of the cornea is lined by endothelium, or cells that normally pump fluid out of the cornea. These endothelial cells keep the cornea thin and clear, allowing light to pass through the cornea and into focus clearly on the retina. If the endothelium is damaged or unhealthy, the cornea can become thick and cloudy, and the vision can become blurry. This layer can be replaced by special corneal transplant techniques, called an endothelial keratoplasty (EK), or a partial thickness cornea transplant of the endothelium. Two techniques, Descemet’s stripping endothelial keratoplasty (DSEK) and Descemet’s membrane endothelial keratoplasty (DMEK), can be used in these circumstances. Both techniques are depicted below, where the outer black circle is the cornea, the red line is the size of the endothelial transplant, the blue area is the iris, and the black circle represents the pupil.
DSEK – Descemet’s Stripping Endothelial Keratoplasty
DSEK is a partial thickness transplant, where the unhealthy endothelium and underlying Descemet’s membrane are replaced by a slightly thicker donor tissue (the red curved line below). This donor tissue includes endothelium, Descemet’s membrane, and a small portion of the corneal stroma. This extra bit of stroma allows easier tissue handling during the operation. The DSEK tissue is represented in the image below by the thick red line, attached to back of a curved cornea. A gas bubble is typically used to float the tissue into the proper position within the eye. The visual recovery is more rapid than with a full thickness cornea transplant.
DMEK – Descemet’s Membrane Endothelial Keratoplasty
DMEK is a highly specialised modification of DSEK, where the unhealthy endothelium and Descemet’s membrane are anatomically replaced by donor endothelium and Descemet’s membrane. There is no extra bit of corneal stroma transplanted. Notice the thinner red line in the image below, representing the thin DMEK tissue attached to the back of a curved cornea. It offers some benefits over DSEK, including more rapid visual recovery and a higher likelihood of obtaining the full vision potential of the eye. In addition, there appears to be a lower rate of tissue rejection with the DMEK procedure than with DSEK or other forms of corneal transplantation.
Anterior Lamellar Corneal Transplants
The superficial layers of the cornea include the surface epithelium, Bowman’s membrane, and the middle stroma layer. The stroma layer can be damaged due to scarring or excessive thinning. If the back surface of the cornea is healthy, then the superficial damaged cornea can be replaced by a partial thickness transplant technique called anterior lamellar keratoplasty (ALK).
DALK – Deep Anterior Lamellar Keratoplasty
DALK is a partial thickness transplant, where the unhealthy stroma, Bowman’s membrane, and epithelium are replaced by donor stroma, Bowman’s membrane and epithelium. The patient’s own Descemet’s membrane and endothelium remain in place, reducing the risk of tissue rejection. This tissue is held in position by several microscopic stitches, similar to a full thickness corneal transplant.