Partial Thickness Corneal Transplant
Partial thickness corneal transplant (DSAEK) is a procedure where there is a selective replacement of only the endothelium and a thin layer of posterior stroma for patients with endothelial diseases like Fuchs' corneal dystrophy, or corneal edema after cataract surgery.
Why the Procedure is Performed
This procedure is preferred to the corneal transplant procedure (PKP) in appropriate patients due to a much faster recovery, and greatly decreased risks of complications. In treating patients with corneal endothelial dysfunction, the standard of care has been corneal transplant surgery (PKP), a procedure which replaces the full thickness of the cornea. With the exception of tissue quality and suturing techniques, few improvements have been made within the last 50 years. PKP has several well known disadvantages such as unpredictable refractive outcomes, a prolonged recovery that often takes a year, a permanent susceptibility to trauma, to mention a few.
Partial thickness corneal transplant (DSAEK) has been perfected over the last decade. In 1998, Dutch ophthalmologist Dr. Gerrit Melles developed a way to strip just Descemet's membrane from the cornea, and implant a manually dissected donor disc. The initial technique represented a definite improvement over PKP, but was very surgeon dependent, tedious, and required extensive manual dissection of the donor's cornea. More recently Dr. Mark Gorovoy automated endothelial keratoplasty using a microkeratome, making the corneal dissection very reproducible, like creating a LASIK flap. Automating the dissection creates a smoother surface on the donor cornea than what can be reliably obtained with a manual dissection. This translates in to a better optical interface.
The procedure starts by peeling off Descemet's membrane through a 4.5 mm limbal incision, leaving a smooth corneal host interface. The posterior donor tissue is then prepared with the microkeratome that, with a deep cut, removes the majority of the stroma. The posterior lamellar donor button consists of endothelium, Descemet's membrane, and 100 to 200um of stromal tissue. The donor disc is folded and inserted in the anterior chamber. The donor disc is then pressed into place with an air bubble, and remains fixed in place by the suction action of the endothelium.
The procedure is performed through a small limbal incision like that used for cataract surgery, no extensive corneal suturing is required. There is no risk of exposed or infected corneal sutures. Compared to PKP, there is much greater wound strength which is very important in elderly patients at risk of falling.
Postoperative care for DSAEK is similar, but less tedious than that of PKP for both surgeon and patient. Although techniques may differ slightly from surgeon to surgeon, most have found the results of DSAEK to be significantly better than PKP. Some consider it to be the standard of care for any patient suffering with Fuchs' corneal dystrophy, or post-cataract corneal decompensation. With DSAEK the speed of visual recovery is significantly improved. Typically the patient's vision recovers in 2 -to-4 months with BSCVA of 20/40 or better with little change in their spectacle correction. The refractive outcomes are far more predictable, since there is no significant induced astigmatism. Potentially, there is less risk of rejection.