Penetrating Keratoplasty (Full-thickness corneal transplant)
This is the standard method of replacing corneal tissue, first carried out over 100 years ago. A full-thickness, central, circular disc of cornea is removed and replaced with the same healthy tissue from a donor cornea. The new cornea is held in place with very fine nylon stitches. The stiches, unless they cause problems, will typically stay in place for 18-24 months after surgery. They are easily and painlessly removed as a simple out-patient procedure, usually one or two at a time.
Penetrating keratoplasty is a fairly successful procedure, but has some significant disadvantages. Firstly, if the inside lining of the cornea (the endothelium) is healthy, an operation which avoids replacing it (Deep Anterior Lamellar Keratoplasty) will give similar results, without any risk of replacemnt endothelium being rejected.
Corneal Transplant Overview
Deep Anterior Lamellar Keratoplasty (DALK)
This is very similar in effect and follow up to a full thickness transplant. In a full thickness transplant, one of the major causes of the transplant failing is rejection of the endothelium (the innermost layer of the cornea). If that layer is healthy, but the wall of the cornea is scarred or mis-shapen, replacing all of the thickness of the cornea except the innermost layers greatly reduces the risk of rejection. A DALK involves replacing very nearly the full thickness of the cornea, leaving behind an extremely thin layer on the inside of the cornea. This is a more difficult procedure than a full thickness transplant, but offers better long-term safety.
Descemet's Stripping Endothelial Keratoplasty (DSEK)
This procedure revolutionised surgery for corneal endothelial problems. No longer is it necessary to cut a full thickness hole in the front of the eye and stitch a replacement cornea in place for eyes with a healthy and potentially clear corneal wall (stroma). In this procedure, a thin sliver of the inside of a donor cornea is used to replace unhealthy endothelium, afer the patient's unhealthy endothelium has been stripped off.
DSEK gives good visual results, with many eyes getting good enough vision to drive afterwards. The recovery time is mesured in months rather than years it takes a penetrating keratoplasty to settle.
One minor problem with DSEK is that the new piece of cornea may be very mildly wrinkled or distorted, particularly if the tissue is slightly thick. Currently lots of work is being done on ways of making the transplanted tissue as thin as possible.