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Surgeons introduce new endothelial keratoplasty technique
Pre-Descemet's endothelial keratoplasty involves transplantation of the endothelium, Descemet's membrane and the novel pre-Descemet's layer.
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Corneal transplantation continues to remain largely in the domain of full-thickness corneal tissue replacement, namely penetrating keratoplasty, with 36,716 such procedures performed in 2012 in the United States, according to a report from the Eye Bank Association of America. However, in the recent past, interest among corneal surgeons has focused on newer, modified lamellar corneal procedures that can be largely categorized as anterior lamellar keratoplasty and posterior lamellar keratoplasty, divided for the most part by Descemet’s membrane. These lamellar procedures may be termed as selective tissue transplantation, in which only the diseased portion of the human cornea is surgically replaced with similar healthy donor corneal tissue. The number of all such lamellar procedures totaled 26,880 in the U.S. in 2012.
Recently, the pre-Descemet’s layer (Dua’s layer, or PDL) was described and defined, and its role in lamellar procedures has attracted attention and interest. In anterior lamellar keratoplasty procedures, such as total anterior lamellar keratoplasty or deep anterior lamellar keratoplasty, the PDL in most instances would separate along with the Descemet’s membrane and endothelium, contrary to the belief that the Descemet’s membrane was being laid bare. In Descemet’s membrane endothelial keratoplasty, only the Descemet’s membrane and healthy donor endothelium without the PDL are transplanted onto the recipient cornea.
DMEK is the newest posterior lamellar keratoplasty procedure that is devoid of any donor stromal tissue. Posterior lamellar keratoplasty procedures had their origin with deep lamellar endothelial keratoplasty, which progressed to Descemet’s stripping endothelial keratoplasty and now DMEK. The term endothelial keratoplasty largely encompasses the two major players, namely DSEK and DMEK. DMEK requires a new skill set to successfully unroll the donor Descemet’s membrane and attach it to the recipient cornea. Including the PDL with Descemet’s membrane in endothelial keratoplasty would add tissue rigidity and potentially facilitate the procedure.
In this column, Drs. Agarwal and Dua describe their technique of pre- Descemet’s endothelial keratoplasty. The material is derived from a presentation made at the European Society of Cataract and Refractive Surgeons meeting in Amsterdam, Netherlands, in October.
Thomas “TJ” John, MD
OSN Surgical Maneuvers Editor
Amar Agarwal
Harminder Dua
Endothelial keratoplasty has evolved briskly, and the data accumulated over the past 10 years demonstrate that all the posterior lamellar techniques of endothelial replacement yield superior visual, topographic and tectonic results compared with penetrating keratoplasty. We report a novel method of endothelial keratoplasty in which the endothelium, Descemet’s membrane and pre-Descemet’s layer (Dua’s layer, now termed PDL) are transplanted; we call it pre-Descemet’s endothelial keratoplasty (PDEK).
Early evidence to support the existence of a distinct pre-Descemet’s layer of tissue was presented by Dua et al in 2007 and followed by a detailed paper wherein evidence is presented to further support the presence of the distinct PDL. Others have reported it as “residual stroma” attached to Descemet’s membrane when separation is caused with injection of air. The use of air to cause a separation of the Descemet’s membrane for obtaining tissue for Descemet’s membrane endothelial keratoplasty has been reported before, as it was believed that the air separated Descemet’s membrane from stroma. In the PDEK procedure, the objective is to retain the PDL with the endothelium-Descemet’s membrane complex, thereby providing additional support to the graft tissue used for the procedure. The presence of this layer, with its characteristics of relative rigidity and toughness, allows easy intraoperative handling and insertion of the tissue because it does not tend to scroll as much as the Descemet’s membrane alone.
The most popular Descemet’s membrane-barring technique is the big bubble method, in which the big bubble forms a cleavage plane, leaving the Descemet’s membrane bare for the dissection in lamellar keratoplasties. The Descemet’s membrane is truly laid bare only when a type 2 (pre-Descemetic) bubble is created between the PDL and the Descemet’s membrane. In the PDEK procedure, a type 1 big bubble, which typically lies between the PDL and the posterior corneal stroma, is formed, thereby creating a dome of PDL-Descemet’s membrane-endothelial complex above the air bubble.
Donor graft preparation
A corneoscleral disc with an approximately 2-mm scleral rim is dissected from the whole globe or obtained from an eye bank. A 30-gauge needle attached to a syringe is inserted from the limbus into the mid-peripheral stroma (Figure 1, top left, top middle). Air is slowly injected into the donor stroma until a type 1 big bubble is formed; this is a well-circumscribed, central dome-shaped elevation measuring 7 mm to 8.5 mm in diameter (Figure 1, top right, bottom left). It always starts in the center and enlarges centrifugally, retaining a circular configuration. Trephination of the donor graft is done along the margin of the big bubble (Figure 1, bottom middle). The bubble wall is penetrated at the extreme periphery, and trypan blue is injected into the bubble to stain the graft, which is then cut all around the trephine mark with a pair of corneoscleral scissors (Figure 1, bottom right) and covered with the tissue culture medium. The graft is loaded into an injector when ready for insertion.
Recipient bed preparation
After administering peribulbar anesthesia, the recipient corneal epithelium is debrided, if grossly edematous, for better visualization (Figure 2, top left). A trephine mark is made on the recipient cornea respective to the diameter of the Descemet’s membrane to be scored on the endothelial side (Figure 2, top middle). A 2.8-mm tunnel incision is made at 10 o’clock near the limbus. The anterior chamber is formed and maintained with saline injection or infusion. The margin of the Descemet’s membrane to be removed is scored initially from the endothelial side with a reverse Sinskey hook (Figure 2, top right). Once an adequate edge is lifted, non-toothed forceps are used to gently grab the Descemet’s membrane at its edge, and the graft is separated from the underlying stroma in a capsulorrhexis-like circumferential manner. The peeled Descemet’s membrane is then removed from the eye.
Figure 1. PDEK donor graft preparation. Top: (left) A 30-gauge needle inserted at the limbus on the endothelial side. (Middle) Needle advanced into the stroma. (Right) Intrastromal air injection. Bottom: (left) Central dome-shaped type 1 big bubble formed. (Middle) Trephination of endothelial graft performed. (Right) Endothelial-Descemet’s membrane complex with pre-Descemet’s layer stained with trypan blue and cut with corneoscleral scissors.
Images: Agarwal A, Dua H
Figure 2. Recipient bed preparation and graft insertion. Top: (left) Preoperative image of the eye with endothelial decompensation. Epithelium debridement being done. (Middle) Trephine marking done on the cornea. (Right) Descemet’s membrane scored and stripped with reverse Sinskey hook. Bottom: (left) Graft lenticule is loaded into an injector. (Middle) Intraoperative manipulation of the graft for proper positioning. (Right) Air injected underneath the donor graft lenticule to lift it toward the recipient posterior stroma. Anterior chamber filled with air.
Figure 3. Preoperative, postoperative and OCT picture (day 1) of a PDEK case.
Donor lenticule implantation
The donor lenticule roll (endothelium-Descemet’s membrane-PDL) is inserted in the custom-made injector (Figure 2, bottom left) and slowly pushed up the lumen of the nozzle. The injector is improvised from an IOL implant injector by removing the sponge tire and spring and reattaching the sponge tire, to prevent any back suction and inadvertent damage to the donor graft. Using the injector, the graft roll is injected in a controlled fashion into the anterior chamber. The donor graft is oriented endothelial side down and positioned on to the recipient posterior stroma by careful, indirect manipulation of the tissue with air and fluid (Figure 2, bottom middle). Once the lenticule is unrolled, an air bubble is injected underneath the donor graft lenticule to lift it toward the recipient posterior stroma. The anterior chamber is completely filled with air for the next 30 minutes, followed by an air-liquid exchange to pressurize the eye (Figure 2, bottom right). The eye speculum is finally removed, and the anterior chamber is examined for air position. The patient is advised to lie in a strictly supine position for the next 3 hours.
PDEK entails the inclusion of the PDL in the donor graft, thereby providing the benefits of DMEK, such as speedy visual recovery, and overcoming the disadvantages posed by DMEK. PDEK takes ultra thin-DSEK to a “thinner level” while retaining its advantages but not requiring sophisticated instrumentation and a keratome. Spectral-domain optical coherence tomography in vivo analysis of PDEK grafts showed mean graft thickness after 1 month to be 28 ± 5.6 µm, which is larger than the conventional DMEK graft and less than the ultra-thin Descemet’s stripping automated endothelial keratoplasty graft. In PDEK, the additional layer thickness with endothelium-Descemet’s membrane complex is less than the overall thickness of the DSEK or ultra-thin DSAEK graft. This is compatible with a faster visual recovery. PDEK will also allow the use of young donor eyes (younger than 50 years) with their higher complement of endothelial cells, which are considered unsuitable for DMEK due to an increased risk of Descemet’s membrane damage during harvesting. A comparison of the preoperative and postoperative clinical slit lamp pictures of the eye, along with OCT images, shows a clear graft on the first postoperative day (Figure 3). Some aspects of the different endothelial keratoplasty techniques are demonstrated in the Table.
Long-term studies evaluating different parameters such as endothelial cell loss over time, interface, detachment rates and final visual acuity, including higher-order aberrations and contrast sensitivity, are required to establish a place for PDEK in corneal transplantation surgery.