Twelve surgical tips to assist DALK, TALK procedures

These tips can be used alone or in combination to perform a safer procedure.

Thomas John

Selective tissue corneal transplantation appears to be the direction that most corneal specialists would like to pursue in their continued efforts to visually rehabilitate their patients with cornea-related visual compromise or blindness.

When it comes to selective tissue corneal transplantation, one may say, “It is all about the endothelium,” in the corneal “equation” for vision restoration. If the endothelium is functionally compromised or damaged, then one would consider endothelial keratoplasty, or if the endothelium is healthy, one may choose anterior lamellar keratoplasty in the presence of visually significant stromal alterations and avoid a full-thickness corneal replacement procedure. Figure 1 shows the John-Malbran classification for anterior lamellar keratoplasty. When performing deep anterior lamellar keratoplasty (DALK) or total anterior lamellar keratoplasty (TALK), there can be several surgical hurdles that may hamper the endpoint of obtaining a completely exposed, intact recipient Descemet’s membrane.

In this column, I provide several surgical tips that one may consider using alone or in combination to try to perform safer DALK and TALK procedures.

Figure 1. John-Malbran classification of anterior lamellar keratoplasty. Images: John T

Surgical tip No. 1

Preoperative corneal optical coherence tomography measurements of the peripheral cornea will help determine the depth of corneal partial-thickness trephination without perforating the recipient Descemet’s membrane.

Surgical tip No. 2

General anesthesia may be preferred over topical anesthesia or monitored anesthesia care. Complete immobilization will help prevent inadvertent patient movement that may result in an accidental Descemet’s membrane tear, especially when one is performing deep stromal dissection close to the Descemet’s membrane.

Surgical tip No. 3

Perform peripheral host corneal stab incision entry into the anterior chamber after partial-thickness trephination and before intrastromal air injection to create a big bubble. In the event air injection results in complete whitening and air-induced opacification of the cornea, this would make it difficult to enter the anterior chamber with a super blade without the added risk of potential iris damage due to the blind entry into the anterior chamber.

Surgical tip No. 4

An anterior lamellar keratoplasty surgeon should consider familiarizing himself with various surgical techniques (Figures 2 to 7) for stromal dissection, stromal separation from the Descemet’s membrane and complete exposure of the patient’s Descemet’s membrane. Such an approach will usually be helpful because a single anterior lamellar keratoplasty technique may not work consistently in fully exposing the recipient Descemet’s membrane. Additionally, use available surgical textbooks as another learning resource.

Figure 2. Use of air, big-bubble technique. Intrastromal needle insertion and forced injection of air to create a big bubble within the corneal stroma to separate the corneal stroma from the Descemet’s membrane. Insert: Intrastromal insertion of a 30-gauge needle.

Figure 3. Use of air, big-bubble technique. Sterile balanced salt solution is used to rinse the interface, namely, the inner surface of the donor cornea devoid of endothelium and the recipient Descemet’s membrane. Insert: Completed view of the TALK procedure.

Figure 4. Corneal OCT after TALK procedure, showing uniform attachment of the Descemet’s membrane to the donor corneal stroma that is devoid of donor endothelium, without any pseudo-chamber, and the donor-recipient interface and the Descemet’s membrane-endothelial complex are visible in the OCT image and the postop photo (insert).

Figure 5. Fluid technique: Forced injection of sterile balanced salt solution intrastromally after stromal staining with indocyanine green dye, and a layered dissection is carried out until the bare Descemet’s membrane is exposed.

Figure 6. Viscoat technique: Use of Viscoat injection to separate the stroma from the exposed Descemet’s membrane. Air injection was tried before the use of Viscoat.

Figure 7. Trypan blue staining of the recipient corneal stroma (main figure), donor corneal endothelium (upper left insert) and a layered dissection approach are used to fully expose an intact recipient Descemet’s membrane (upper right insert).

Surgical tip No. 5

Using advanced-design surgical instruments can help minimize potential intraoperative complications, including Descemet’s membrane tear and conversion to a penetrating keratoplasty. Using a needle to induce a big bubble can cause damage to the Descemet’s membrane due to the sharp edge of the needle. Instead, using the combination of a blunt 30-gauge tracker with a larger 27-gauge cannula (John ALK tracker and cannula, one- or three-hole, ASICO) creates a tight fit within the deep corneal stroma and helps facilitate the formation of a big bubble.

Surgical tip No. 6

While excising the last part of the deep corneal stroma after exposing the bare Descemet’s membrane, accidental tearing of the Descemet’s membrane can occur due to the sharp edge of the scissors and may result in the conversion to a full-thickness penetrating keratoplasty. To avoid tearing the Descemet’s membrane, one should consider lifting the stromal edge away from the Descemet’s membrane using a pair of 0.12 forceps and gently excising the tissue, being careful to keep the tip of the Vannas scissors away from the Descemet’s membrane.

Alternatively, one can use the John ALK scissors (ASICO). The inferior blade has a terminal disk that will gently push the Descemet’s membrane away from the sharp tip of the superior blade and hence protect the Descemet’s membrane at all times during stromal excision close to the Descemet’s membrane. Right- and left-handed John ALK scissors are used to complete the circular stromal excision.

Surgical tip No. 7

Use of dye, indocyanine green or trypan blue, during stromal dissection and donor tissue preparation is recommended (Figures 5 and 7). The donor endothelium is exposed to trypan blue, and this staining technique helps to visualize the endothelial layer and facilitates the removal of the donor Descemet’s membrane and endothelium. Further, staining of the recipient stroma helps in the layered approach of recipient stromal dissection and exposure of the bare Descemet’s membrane. Staining of the recipient stroma is especially useful in forced hydrodissection techniques using fluid (Figure 5).

Surgical tip No. 8

It is essential to adequately irrigate the inner surface of the donor cornea and the outer surface of the recipient Descemet’s membrane before attaching the donor corneal disc to the recipient Descemet’s membrane bed to ensure the donor-host interface is free of any debris.

Surgical tip No. 9

Make sure that the recipient Descemet’s membrane lines the inner surface of the donor corneal stroma uniformly, without the formation of any pseudo-chamber. This can be confirmed with an intraoperative slit lamp when available. Also, if necessary, air can be injected into the anterior chamber to push the patient’s Descemet’s membrane against the donor cornea. However, if air is injected into the anterior chamber, make sure to aspirate the air at the end of the procedure to prevent any postoperative pupillary block.

Surgical tip No. 10

Decompress the anterior chamber repeatedly as needed during stromal excision.

Surgical tip No. 11

Use Viscoat (chondroitin sulfate, sodium hyaluronate, Alcon) as needed to protect the Descemet’s membrane during stromal dissection. Fully irrigate the Viscoat off the Descemet’s membrane before placement of the donor cornea.

Surgical tip No. 12

Minimize induced surgical astigmatism by suture tension adjustment at the end of the procedure with the use of a circular fiber optic light or the end of a sterile safety pin.

References:

• John T, ed. Corneal Endothelial Transplant DSAEK, DMEK & DLEK. Panama City, Panama: Jaypee-Highlights Medical Publishers; 2010:1-428.
• John T, ed. Lamellar Corneal Surgery. New York, NY: McGraw-Hill Companies; 2008.
• John T, ed. Step by Step Anterior and Posterior Lamellar Keratoplasty. New Delhi, India: Jaypee Brothers Medical Publishers; 2006:1-297.
• John T, ed. Surgical Techniques in Anterior and Posterior Lamellar Keratoplasty. New Delhi, India: Jaypee Brothers Medical Publishers; 2006:1-687.

• Thomas John, MD, is a clinical associate professor at Loyola University at Chicago and in private practice in Oakbrook, Tinley Park and Oak Lawn, Ill. He can be reached at 708-429-2223; fax: 708-429-2226; e-mail: tjcornea@gmail.com.
• Disclosure: Dr. John receives a small royalty from Jaypee Publishers and ASICO.