What is the difference between Penetrating Keratoplasty (PK) and Deep Anterior Lamellar Keratoplasty (DALK)?
Penetrating Keratoplasty (PK) essentially transplants the full cornea’s thickness including all stroma, Descemet’s membrane, and endothelial cells (click here for a description of all the cornea’s layers). Deep Anterior Lamellar Keratoplasty (DALK) is used in diseases that exclusively affect the middle stromal layer. In these diseases, the stroma is sick, cloudy, or deformed, but the inner layers (Descemet’s membrane and endothelial cells) are healthy. Purely stromal diseases include keratoconus and some corneal dystrophies.
How is DALK performed?
A circular cookie cutter-like blade cuts the central 8 to 9 mm portion of the cornea. The cut is taken down through the stroma but the endothelium is left intact. This procedure is very delicate because the endothelium is like a piece of Saran wrap, but thinner and far, far more fragile. If the endothelium develops a break, the surgeon likely has to remove it and place a full-thickness PK style transplant. If the endothelial preservation is successful, the DALK transplant is then sewn into place with 16 carefully placed micro-sutures.
What patients need a PK instead of a DALK?
If the corneal endothelium is unhealthy or we can’t prove its health due to a poor view through a cloudy stroma, we would recommend a PK instead of a DALK. This is because if the endothelium is not healthy, the DALK transplant would never heal properly, the graft would fail, and the surgery would have to be repeated with a PK.
In terms of effect, what are the similarities and differences between DALK and PK? What are the advantages of DALK?
The results between DALK and PK are very similar. Most importantly the visual outcomes are the same. The average best-corrected vision for both is 20/30 with one-third of patients requiring a hard contact to see their best. Astigmatism for both averages about 4 diopters with a typical range varying between 2 to 10 diopters. Those with higher amounts of astigmatism require a hard contact lens to see rather than just glasses. The intraoperative and postoperative risks are similar but slightly less with DALK.
The major advantage of having DALK and retaining the patient’s own endothelium is that the transplant is less likely to fail from rejection. One of the main reasons a graft fails after a rejection episode is from loss of these endothelial cells. DALK grafts, therefore, will generally last at least twice as long as PK grafts.
Long term use of corticosteroid eye drops may cause elevated eye pressure (glaucoma) or early cataract formation. Because DALK rejection is less likely, we don’t have to use postoperative anti-rejection corticosteroid eye drops as frequently so glaucoma and cataracts are less common.
The time to visual recovery is less for DALK compared to PK. Steroid drops also delay wound healing. DALK wounds heal quicker since they require fewer corticosteroid drops. Once the wound is fully healed, we can remove the stitches and attain faster visual recovery. PK transplants usually take a year for full visual recovery. DALK transplants take an average of 6 to 8 months.
Click here for an overview of the various types of corneal transplantation surgery.
How long do DALK and PK transplants last?
PK transplants routinely last 10 to 20 years. Depending on how healthy an eye is, some data suggests DALK transplants can last twice as long. They may last less than one year if a graft rejection is severe enough, but rejection is less likely in DALK transplants.
How often is DALK technically possible to surgically perform?
The corneal endothelium cannot be separated from the stroma or breaks during attempted DALK in about 10 to 20% of cases. A full-thickness PK is necessary if this dissection isn’t successful.
How well will I see with a PK / DALK transplant?
Vision appears to be similar between PK and DALK transplants, with most seeing at least 20/30 with correction. Up to 10% of people attain 20/20 vision with correction.
Will I need glasses after PK / DALK transplant? Could laser vision correction be done to reduce any postoperative need for glasses?
Most people need glasses after the DALK or PK. About one-third of transplant patients need rigid contacts instead of glasses to see well due to astigmatism. Some people are candidates for advanced surface ablation (ASA), a laser procedure similar to LASIK, to minimize their dependence on glasses or contacts after surgery.
How long does it take to recover after DALK and PK? What is the follow-up schedule?
DALK transplants are usually fully healed with visual recovery within 6 to 8 months when it is safe to remove all sutures. Because it involves more corneal layers and tends to need more steroid drops which can delay healing, we typically don’t remove all of the sutures on a PK until at least 12 months.
After both DALK and PK, it takes between 1 to 4 weeks for the surface epithelium to heal. Once the epithelium heals, patients are examined every 2 months. Patients then need to see an eye doctor at least yearly and more often if taking corticosteroid eye drops. Any new symptoms such as redness, sensitivity to light, vision changes, or pain need to be seen immediately since any of these could be a sign of rejection or other complications.
Do I need to go on immunosuppressive medications after DALK or PK surgery?
Because there is no blood flow to the clear cornea, it is mostly invisible to the immune system. Corneal transplants therefore usually only need steroid anti-inflammatory eye drops to prevent rejection. Systemic immunosuppressive therapy is only needed in very rare situations in patients with very aggressive immune systems. DALK is even less likely than PK to require such extra measures.
Does a rejection episode mean that I will lose my cornea transplant?
Most people don’t lose their transplant, but an untreated rejection episode can put the transplant and even the eye at risk. The key is to recognize the early signs of rejection and seek prompt care. Patients are instructed to RSVP: come see us for new Redness, Sensitivity to light, Vision reduction, or Pain. For the rest of their life, any patient with a corneal transplant needs to seek immediate care if they ever develop these symptoms.
If detected early, a rejection episode can most likely be reversed and eliminated without permanent, vision-threatening graft damage. A rejection requires increased corticosteroid drops and sometimes other medications. If a patient has any of the RSVP symptoms, it is critical they come to see us, rather than simply self-treat by increasing the drop usage at home because not all pain is related to rejection. In rare cases, these symptoms could signify an infection which would need an entirely different set of medications to prevent severe damage to the eye.