Newer techniques, instruments aid lamellar keratoplasty procedures

The 100th Surgical Maneuvers column focuses on DALK and DMEK.

This issue’s installment marks Thomas “TJ” John, MD’s, 100th column as editor of Surgical Maneuvers for Ocular Surgery News. These instructive clinical features are a cornerstone of the publication and an aide to ophthalmic surgeons’ surgical practice. I would like to thank and congratulate TJ for his contribution to the publication and to the promotion of better surgical skills for ophthalmologists around the world.

Richard L. Lindstrom, MD
Chief Medical Editor

Lamellar keratoplasty offers a way to selectively exchange diseased or damaged corneal tissue with similar, healthy donor tissue, thus retaining the remainder of the patient’s corneal tissue. Lamellar keratoplasty encompasses both anterior and posterior lamellar keratoplasty, or ALK and PLK. Depending on the amount of corneal tissue being replaced, ALK can range from superficial to total, according to the John-Malbran ALK classification. PLK primarily includes endothelial keratoplasty, namely, Descemet’s stripping endothelial keratoplasty and Descemet’s membrane endothelial keratoplasty. Although these procedures are attractive to the patient, they pose several challenges to the operating surgeon. Helpful surgical techniques and advanced surgical instruments that are better suited for these procedures somewhat decrease the complexity and increase the overall success.

In this column, we shall focus primarily on two major lamellar keratoplasty procedures: deep anterior lamellar keratoplasty and Descemet’s membrane endothelial keratoplasty.

DALK

The surgical goal here is to remove all corneal stroma within the trephination area, leaving an intact recipient Descemet’s membrane and healthy endothelium. The big bubble technique utilizes air to separate corneal stroma from the Descemet’s membrane. The patient’s cornea is trephined to about 300 µm to 400 µm depth, depending on the overall corneal thickness while avoiding full corneal penetration. A 27-gauge sterile needle shaft is bent with the bevel facing down. The needle is introduced through the trephination, entering the deeper regions of the cut stroma and pushing steadily forward such that it is separated from the Descemet’s membrane with a thin layer of the stroma. Once the needle tip reaches the corneal paracentral region, gently lift the knee of the bent needle such that the bevel is in close contact with the stroma and air is injected in multiple steady bolus until the outer boundary of the air bubble matches the circular trephination (Figure 1). This retains a view to the anterior chamber through the clearer peripheral corneal rim.

Using a 15° super blade with the sharp edge facing the ceiling, a quick nick into the apex of the cornea is made, resulting in partial collapse of the big bubble (Figure 2). Next, enter the anterior chamber with a 15° super blade and decompress the anterior chamber by controlled aqueous egress (Figure 3). Viscoat (chondroitin sulfate-sodium hyaluronate, Alcon) injection into the corneal opening fills the iatrogenically created space between the stroma and Descemet’s membrane (Figure 4). Gently lyse any fine adherences between the stroma and Descemet’s membrane and complete the dissection with an ALK spatula past the trephination mark (Figure 5). Use the John ALK scissors (ASICO) with a circular disc at its tip, which pushes the Descemet’s membrane away from the sharp blades, thus preventing Descemet’s membrane tear. Irrigate both the recipient Descemet’s membrane and the donor corneal disc devoid of Descemet’s membrane and endothelium before suturing it in place (Figure 6). Use intraoperative slit lamp to ascertain uniform attachment of the donor-recipient interface and intraoperative ring lights (Mastel) to minimize induced, iatrogenic corneal astigmatism (Figures 7 and 8).

Surgical pearls

Once the needle is housed within the corneal stroma, avoid any unnecessary needle movements that can jeopardize a tight fit and lessen the chance of an optimal big bubble. Ascertain firm housing of the needle hub to the syringe to avoid air leaks. Inject air steadily and avoid making the entire cornea opaque, which will compromise the anterior chamber view. Gently lift the knee of the needle before air injection. These maneuvers optimize big bubble formation. Decompress the anterior chamber before Viscoat injection because this facilitates the posterior bulging of the Descemet’s membrane toward the anterior chamber. Dissect past the trephination cut, which will facilitate excision of the recipient cornea and decrease inadvertent tear in the Descemet’s membrane. Gently lift the stroma away from the Descemet’s membrane while excising the stroma. Alternative to the needle technique is the use of a tracker and cannula.

DMEK

In DMEK, only the Descemet’s membrane and the endothelium are replaced with similar healthy donor tissue. Use the John DMEK Dexatome spatula (John DMEK set, Bausch + Lomb) to remove the recipient Descemet’s membrane and only touch the folded Descemet’s membrane and minimize any contact with the recipient exposed inner corneal stroma, thus contributing to a superior interface and better quality of vision (Figure 9). Staining donor Descemet’s membrane with Vision Blue (trypan blue, DORC) augments visualization of the Descemet’s membrane within the recipient anterior chamber (Figure 10). If the view is suboptimal, remove the epithelium. Deposit the donor Descemet’s roll in the central deepest part of the anterior chamber and unroll it by using the John Smoother (Bausch + Lomb) on the outer corneal dome (Figure 11). The smoother helps ascertain centration and unroll the Descemet’s membrane without the use of any air bubble (Figure 12). Attach the donor Descemet’s membrane to the recipient corneal stroma with a large air bubble. Intraoperative slit lamp helps to confirm uniform attachment of the Descemet’s membrane to the corneal stroma (Figure 13).

Surgical pearls

The John DMEK Dexatome spatula, due to its unique curvature, is better suited to remove the patient’s Descemet’s membrane because it can reach all areas of the inner corneal dome with ease as compared with a straight reverse Sinskey hook.

Use limited fluidics within the anterior chamber to unroll the Descemet’s membrane. The John DMEK Smoother works well with centration of the donor Descemet’s membrane disc and in effectively unrolling the Descemet’s membrane without the use of air bubble. If the trypan blue-stained Descemet’s membrane does not easily unroll, wait a few minutes for the trypan blue to get diluted with the aqueous and then the Descemet’s membrane will usually unroll more easily with the use of the DMEK Smoother. Confirm that the cannula tip is between the donor Descemet’s membrane and the iris surface before injecting a large air bubble to attach the Descemet’s membrane.

Lamellar keratoplasty is an old surgical procedure with newer surgical techniques and instrumentation. Utilization of newer instruments helps the surgeon complete the lamellar keratoplasty procedure effectively with optimal postoperative vision and a happy patient.

For more information:

Thomas “TJ” John, MD, is a clinical associate professor at Loyola University at Chicago and in private practice in Oak Brook, Tinley Park and Oak Lawn, Ill. He can be reached at 708-429-2223; email: tjcornea@gmail.com.
Disclosure: John is a consultant to ASICO and Bausch + Lomb and receives a small royalty from ASICO.