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DMEK latest in selective tissue corneal transplantation surgery
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Introduction
Corneal transplantation surgery has achieved new heights in terms of advanced surgical techniques used by corneal surgeons in which only the diseased portion of the cornea is replaced by a similar healthy donor corneal tissue. This is in contrast to penetrating keratoplasty in which the full thickness of the cornea is replaced regardless of the corneal layer that is involved in the disease process.
 Thomas John |
I have introduced a new terminology, selective tissue corneal transplantation (STCT), that is defined as the selective removal of the diseased portion of the patient’s cornea and its replacement with anatomically similar healthy donor tissue.
The newer surgical technique of corneal transplantation, namely descemetorhexis with endokeratoplasty (DXEK) or Descemet’s stripping automated endothelial keratoplasty (DSAEK), has gained worldwide acceptance and is rapidly becoming the preferred surgical choice for dealing with corneal endothelial decompensation resulting in corneal edema, bullous keratopathy and loss of best corrected visual acuity. This type of surgical procedure is an example of STCT. This procedure, namely DXEK/DSAEK, is an additive procedure in which the postoperative corneal thickness far exceeds the range of normal corneal thickness and the donor-recipient interface is a stroma-to-stroma interface.
The newer technique of STCT described by Melles and colleagues is called Descemet’s membrane endothelial keratoplasty (DMEK) in which only the Descemet’s membrane and endothelium of the patient’s cornea are replaced by similar healthy donor corneal tissue. This is a more natural form of STCT in which the postoperative corneal thickness should be within the range of normal corneal thickness and donor-recipient interface is Descemet’s membrane to stroma, ensuring a more natural, final anatomic result. However, DMEK has its challenges in terms of the surgical techniques involved in this new procedure.
My guest in this corneal dissection column, Massimo Busin, MD, describes performing DMEK with an emphasis on simplifying the technique, which may help to gradually move DMEK to the forefront of STCT for endothelial decompensation. The technique is based on the concept of the “big bubble,” which was used by Anwar and Teichman to dissect the corneal stroma from the underlying Descemet’s membrane and endothelium when performing anterior lamellar keratoplasty for keratoconus. Dr. Busin’s technique described in this column is substantially different in many ways, however, similar to the big bubble technique for keratoconus, air is used to achieve a complete dissection between the donor Descemet’s membrane and corneal stroma. His technique includes both harvesting the donor tissue and delivering it into place and attaching it to the patient’s cornea. This new DMEK surgical technique needs to be evaluated in larger prospective series looking at the central issue of donor corneal endothelial survival and its comparative outcome to the more established STCT technique of DXEK/DSAEK.
— Thomas John, MD
OSN Corneal Dissection Editor
The preferred anesthesia is with a peribulbar block. However, other forms of anesthesia, including general anesthesia, may be considered by the surgeon.
Step-by-step surgery
The initial surgical step involves the removal of Descemet’s membrane and endothelium from the central part (8 mm to 9 mm in diameter) of the posterior surface of the recipient cornea (Figure 1). Then, the donor cornea is mounted in an artificial anterior chamber, and about two-thirds of the anterior corneal stroma is removed using a microkeratome, the same way it is done when performing DSAEK surgery (Figure 2). This step is not essential but allows the surgeon to convert to DSAEK in case he does not succeed in preparing the endothelial graft. Then, the donor cornea is removed from the artificial anterior chamber and placed with the endothelium facing up.
Next, a 25-gauge needle connected to a 5 cc sterile syringe is inserted, bevel up, into the peripheral donor cornea at about 1 mm from the limbus and advanced in a tangential direction immediately beneath the endothelium for about 2 mm (Figure 3). Air is then injected until detachment of Descemet’s membrane is achieved and a large bubble is obtained (Figures 4 and 5).
 Intraoperative photograph showing the removal of patient’s Descemet’s membrane and endothelium from the central part (8 mm to 9 mm in diameter) of the posterior surface of the cornea. (Reprinted with permission from Jaypee Brothers Medical Publishers) |  The donor cornea is mounted within an artificial anterior chamber, and about two-thirds of the anterior corneal stroma is removed using a microkeratome the same way it is done when performing DSAEK surgery. |  A 25-gauge needle connected to a 5 cc sterile syringe is inserted, bevel up, into the peripheral donor cornea, 1 mm from the limbus, and advanced in a tangential direction immediately beneath the endothelium for about 2 mm. | ||
|  Part of the air is removed from the bubble by using an empty syringe with a 30-gauge needle, achieving a partial collapse of the big bubble. |
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 A few drops of trypan blue (Vision Blue, Dutch Ophthalmic Research Center) are injected into the air bubble created within the donor cornea. |  All of the air is aspirated within the space created by the big bubble. |  Aspiration pressure is maintained to hold the central cornea while moving the sclerocorneal rim with forceps, thus achieving total detachment of the central donor tissue from the peripheral part of the donor cornea. | ||
 The thin donor disc is pulled gently until it protrudes out of the funnel of the Busin glide. |  Coaxial microincision retinal forceps are used to drag the donor graft into the anterior chamber through a nasal clear-cornea incision with a bimanual pull-through maneuver. |  The donor tissue floats as a flat membrane inside the anterior chamber and does not require complex manipulation to unroll it. | ||
 The recipient anterior chamber is air-filled after closing all of the corneal incisions with interrupted 10-0 nylon sutures. | ||||
Next, the surgeon removes part of the air from the bubble by using an empty syringe with a 30-gauge needle and this results in a partial collapse of the big bubble (Figure 6). The same needle is used to inject a few drops of trypan blue (Vision Blue, Dutch Ophthalmic Research Center) into the air bubble (Figure 7). Finally, all the remaining air still present in the space created by the big bubble is aspirated (Figure 8). As a result of the total bubble collapse, the trypan blue stain outlines the portion of Descemet’s membrane that is detached from the donor corneal stroma and allows subsequent, precise punching (trephination) inside the outer limit of dissection.
An 8-mm to 9-mm trephine is used to punch the donor corneal tissue. Aspiration pressure is maintained to hold the central cornea while moving the sclerocorneal rim with forceps, thus achieving total detachment of the central donor tissue from the peripheral part of the donor cornea (Figure 9). The donor corneal disc is composed of the healthy donor corneal endothelium, Descemet’s membrane and a thin layer of the deep corneal stroma. This stromal layer overlying the Descemet’s membrane is thickened by the air injection that was used in this technique.
The stromal disc is held with forceps, which serves as a carrier for the donor endothelium, and the tissue as a whole is transported onto the plate of the Busin glide (Moria). It is then advanced through the distal part of the glide and the thin donor disc is pulled gently until it protrudes out of the funnel of the Busin glide (Figure 10).
Finally, coaxial microincision retinal forceps are used to drag the donor graft into the anterior chamber through a nasal clear-cornea incision with a bimanual pull-through maneuver similar to that used for DSAEK surgery (Figure 11). This entire surgical step is performed under continuous irrigation through an anterior chamber maintainer placed at the 12 o’clock position.
Because the endothelium is lying flat on the stroma during this time, the risk of inserting it upside down is minimized with this maneuver. An additional advantage of this technique is that the bubble formation counteracts the natural tendency of the endothelial layer to roll onto itself. As a result, the donor tissue floats as a flat membrane inside the anterior chamber and does not require complex manipulation to unroll it (Figure 12).
The final step is the air fill, which is completed after closing all of the corneal incisions with interrupted 10-0 nylon sutures (Figure 13). The air in the air-filled anterior chamber is allowed to reabsorb spontaneously over time (usually 2 to 3 days). To prevent a pupillary block, a peripheral iridectomy is performed inferiorly before delivering the donor tissue into the recipient anterior chamber.
Surgical pearls and tips
The DMEK graft tends to curl with the endothelium inward. It is important to recognize the correct tissue orientation before attaching the donor tissue to the recipient cornea.
Trypan blue staining helps in the proper orientation of the donor tissue and in the centration of the donor disc to the patient’s cornea.
Use the same medication as that used after PK, ie, a combination of steroid (dexamethasone 0.1%) and antibiotic (chloramphenicol 0.3%) eye drops, two drops hourly for 2 weeks, then three drops hourly for 2 weeks, then four times daily for 1 month, three times daily for 1 month, two times daily for 1 month and, finally, once daily indefinitely.
Postoperative follow-up, drug regimen
Postoperative medications are the same as for PK or DXEK/DSAEK as per surgeon’s choice, namely topical corticosteroid and antibiotic drops four times daily. If needed, the topical corticosteroid drop frequency may be increased.
References:
- Ide T, Yoo SH, Kymionis GD, Goldman JM, Perez VL, O’Brien TP. Descemet-stripping automated endothelial keratoplasty: effect of anterior lamellar corneal tissue-on/-off storage condition on Descemet-stripping automated endothelial keratoplasty donor tissue. Cornea. 2008; 27:754-757.
- John T. Selective tissue corneal transplantation: a great step forward in global visual restoration. Expert Rev Ophthalmol. 2006;1:5-7.
- John T: Surgical Techniques in Anterior and Posterior Lamellar Corneal Surgery. New Delhi, India: Jaypee Brothers Medical Publishers; 2006.
- John T: Step by Step in Anterior and Posterior Lamellar Keratoplasty. New Delhi, India: Jaypee Brothers Medical Publishers; 2006.
- Melles GR, Ong TS, Ververs B, van der Wees J. Descemet membrane endothelial keratoplasty (DMEK). Cornea. 2006; 25:987-990.
- Thomas John, MD, is a clinical associate professor at Loyola University at Chicago and is in private practice in Tinley Park and Oak Lawn, Ill. He can be reached at 708-429-2223; fax: 708-429-2226; e-mail: tjcornea@gmail.com.
- Massimo Busin, MD, can be reached at Villa Serena Hospital, Via del Camaldolino 8, 47100 Forlì, Italy; 39-347-2449343; e-mail: mbusin@yahoo.com.
