Deep anterior lamellar keratoplasty (DALK) is a form of lamellar corneal transplant that has probably not been given its due within eye care. Whereas most of the lamellar graft procedures (e.g., DSAEK, DMEK) are posterior lamellar transplants used for patients with endothelial decompensation, DALK stands alone as an anterior lamellar transplant. Indicated for anterior pathology, such as keratoectasias, scars and stromal dystrophies, DALK is a surgical alternative to penetrating keratoplasty––not to the DSAEK or DMEK group of procedures.
The chief advantage of DALK lies in its preservation of the host endothelium; it remains intact in the patient. Donor endothelium and Decemet’s membrane (DM) are removed from the graft prior to transplant. This influences two very important postoperative features: the expected lifespan of the graft and the immunologic risk to it.
Concerning the first point, consider that PK grafts are bound by a finite lifespan of roughly 20 years. Thus, given a normal postoperative course without any complications, a PK patient can only expect to keep that graft for two decades at best. Because a DALK procedure does not transplant endothelium, decompensation occurs at physiologic levels and therefore the graft may persist indefinitely.
The second point, regarding the immunology of corneal transplantation, is difficult to briefly outline. But, in appreciating the virtues of DALK, it is necessary to understand two concepts: (1) the only permanent target of immunologic rejection by the host directed against a PK graft is the donor endothelium, and (2) the type of rejection that commonly causes failure of a PK is endothelial targeted rejection.
DALK allows the host to keep his or her own endothelium, and removes this potential long-term stimulus for rejection-derived graft failure from the mix of potential postoperative complications. This greatly reduced risk of rejection enables important trickle-down benefits as well.
While DALK patients are placed on corticosteroids in first year postoperatively, they are less dependent upon them over the long term, and can taper off the regimen more rapidly than is advisable with PK patients. This limits the risk of the steroid-induced side effects, such as glaucoma, cataract and infection.
The Optometrist’s Role
As an OD, what do you need to know for your patients considering this surgery? To be a good candidate, the patient needs to have a relatively uninvolved and well- functioning endothelium. Therefore, patients with penetrating scars or a history of hydrops are not ideal candidates for the procedure, although it still may be attempted.
Even in good candidates, 30% of DALK procedures will be converted intraoperatively to PK as a result of perforations to DM during the surgery. Although DALK has certain advantages over PK, it should be noted that both procedures require sutural fixation of the graft (unlike posterior lamellar grafts). Therefore, both DALK and PK share the same slow visual recovery, relatively high risk of irregular astigmatism and dependence on gas permeable contact lenses. In fact, in many cases, it can be clinically impossible to differentiate a DALK from a PK in the microscope.
Despite a few challenges, DALK has enormous postoperative advantages over PK––athough the complexity of the surgery and slow visual recovery, which are identical to that of PK, has dampened its dissemination in the field. However, when available, it is my opinion that procedure generally is the transplant treatment of choice for any of these pathologies.
Dr. Bronner is a staff optometrist at the Pacific Cataract and Laser Institute in Kennewick, Wash.