Introduction:
In the recent times it is now possible with advanced surgical techniques and instruments, to replace only the selective dysfunctional layer of the cornea. Dr Charuta Puranik is highly skilled in all such lamellar surgical procedures with all the advantages of a corneal transplant but greatly reducing its side effects and long-term complications
DALK is a partial-thickness cornea transplant procedure that involves selective transplantation of the damaged corneal stroma (anterior corneal layer), leaving the native Descemet membrane and endothelium in place.
It is a specialised, highly skilled treatment that selectively replaces the front part of the cornea when it is scarred or distorted.
In ALK, the surgeon dissects the cornea into two thin pieces and removes the front, scarred part. A matching area of healthy tissue from a donor cornea is then used to replace the area that was removed. This procedure is less invasive than a penetrating keratoplasty.
How is it done:
A trephine of an appropriate diameter is used to make a partial-thickness incision into the patient’s cornea, followed by pneumodissection(Big Bubble) or manual dissection of the anterior stroma. This is followed by placement of a graft prepared from a full-thickness punch in which the donor endothelium-Descemet membrane complex has been removed.
Dr Charuta will leave 5% or less of your original corneal thickness after ensuring that it is healthy in structure and functions and replaces the rest with donor tissue.
We have also found that using a femtosecond laser to make the incisions can facilitate the DALK technique eliminating the manual element and permitting better accuracy of the side cuts (Zig Zag/interlocking).
The principal advantages of the interlocking zigzag incision (Femtosecond Laser cut) over the straight incision (Trephine manual cut) are that the zigzag helps align the front surfaces of the donor and recipient corneas, much like a boat floating in a boat dock. This helps to reduce potential visual distortions. The zigzag is like tongue-in-groove construction–creating a stronger wound which results in more secure and faster healing allowing patients to get back to their normal lives sooner and with greater confidence.
Why is it done :
DALK is useful for processes involving the corneal stroma in the presence of healthy endothelium. Examples include corneal ectasia (such as keratoconus in the absence of hydrops), corneal scars that are not full-thickness, and corneal stromal dystrophies
Similar to PK, the graft is secured with interrupted and/or running sutures and is then selectively removed post-operatively.
DALK is our treatment of choice for keratoconus or corneal scars, as long as the inner cell layer of the cornea (the endothelium) is healthy
Procedure:
- Mark the center of the host cornea with a Sinskey hook, and use a calipers to plan the host trephination.
- Trephinate the host cornea to a depth of 90%.
- Insert a 27-gauge needle, or a Fogla dissector followed by a Fogla 25-gauge cannula, into the posterior stroma.
- Inject air to dissect Descemet membrane posteriorly with a large bubble.
- Remove approximately 70% of the anterior stroma using a crescent blade or Devers dissector.
- Create a paracentesis incision to release aqueous.
- After marking the stroma and placing Healon over the mark, make an incision through the mark.
- Inject Healon into the space between the posterior stroma and Descemet membrane. Complete the separation between these two layers using a cyclodialysis spatula.
- Resect the remaining stroma using curved corneal scissors.
- Remove the donor endothelium from the donor graft tissue by manually stripping Descemet membrane, then trephinate the donor tissue.
- Secure the donor graft to the host corneal tissue using interrupted and/or running 10-0 nylon sutures.
- Rotate the sutures to bury the knots, assess the astigmatism using an intraoperative keratometer, and consider placing additional sutures to reduce astigmatic error.
Risks and complication:
Because it is not a full-thickness procedure, the resultant wound is stronger than that of a PK. Leaving the host endothelium intact significantly decreases the risk of endothelial rejection.
The surgery is more complex and requires special skill and experience to perform than PK. Occasionally the Descemet membrane may be perforated intraoperatively in this situation Dr Charuta may convert to a PK.
Rejection with ALK & DALK
Epithelial and stromal cells (the two layers removed with ALK and DALK) can regenerate, while the endothelial cells (back layer) cannot. With ALK and DALK, patients retain their own endothelium so the risk of a patient’s immune system rejecting the tissue is dramatically reduced, which means patients can discontinue use of the corticosteroid eye drops used to prevent rejection sooner. These drops have side effects for some patients that can lead to glacuoma and cataracts, so shortening the time a patient uses these medications will reduce the chances for these adverse effects to occur. Since these drops slow wound healing, stopping sooner means faster healing time and earlier suture removal.