Transplant - DMEK
The first penetrating keratoplasties were developed more than a hundred years ago to replace opaque corneas with clear ones of full thickness. Since the early 1990s, penetrating grafts were gradually replaced with new techniques involving anterior and posterior lamellar grafts. This was possible because for most patients needing keratoplasty only a specific layer of the cornea is damaged. For example, over 35% of patients undergoing grafts suffer from endothelial damage such as Fuchs dystrophy or pseudophakic bullous keratopathy.
A posterior lamellar keratoplasty (PLK) was first attempted by Barraquer in 1950. A corneal flap was cut and lifted on the anterior side allowing for the trephination on the posterior side. A donor posterior lamellar button was then sutured in situ. This technique has gone by several names: Endothelial lamellar keratoplasty (Jones and Culbertson), endokeratoplasty (Busin), and microkeratome-assisted posterior keratoplasty (Azar). In 1998 Melles modernized the technique by performing a posterior lamellar keratoplasty, making a scleral-limbal incision to access the recipient endothelium.
In another major development, a descemetorhexis technique was devised in order to remove only the unhealthy endothelium. The name Descemet’s Stripping Endothelial Keratoplasty (DSEK) was thus proposed. The donor graft was then manually prepared by dissection from the donor cornea.
The preparation of the donor cornea was subsequently automated and performed using a microkeratome on artificial chamber, resulting in the name Descemet's Stripping Automated Endothelial Keratoplasty (DSAEK).
These techniques somewhat succeeded in rehabilitating the patient’s vision but they still had limitations with regard to the perfect anatomical reconstruction because a stroma-stroma interface of variable thickness persisted and prevented a 10/10 postoperative visual acuity from being achieved in the majority of cases.
DMEK (Descemet's Membrane Endothelial Keratoplasty) was developed to restore the anatomy of the cornea. The Descemet endothelium alone is removed from the donor cornea and grafted to the posterior surface of the recipient cornea.
Three distinct operating steps are individualized to perform DMEK.
The first step consists of separating the Descemet endothelium of the donor. The thin endothelial layer is gently peeled from the posterior stroma of the donor cornea while avoiding all contact between the surgical instruments and the endothelium in the central 9 mm (Figure 1).
Then a 9-mm trephine is used to obtain the final endothelial graft, which instantly curls up with the endothelial cells exposed to the outside of the roll that just formed (Figures 2, 3, and 4).
Figure 1: Peeling the Descemet endothelium of the donor after staining with trypan blue.
Figure 2: Endothelial-descemetic roll after peeling. The endothelial cells are on the outside of the “roll.”
Figure 4: This characteristic is due to the elastin fibers present in Descemet's membrane.
Figure 3: The characteristics of Descemet's membrane and its tendency to curl up with the endothelial cells toward the outside are known.
Figure 5: The endothelium-Descemet graft can be likened to a shower mat whereby the small suction cups represent the endothelial cells. In the anterior chamber, the graft must be oriented like the mat on the right, where the endothelial cells face the anterior chamber, not like the mat on the left, where the endothelial cells face the posterior stroma.
The second step involves removing the Descemet endothelium of the recipient. This is done through an air bubble in the anterior chamber by using an inverted Sinskey hook, which makes a descemetorhexis.
The third step involves injecting and positioning the graft onto the posterior surface of the recipient stroma. The graft is first aspirated into a dedicated injector by a so-called “no touch” technique and injected into the anterior chamber through a 3-mm incision (Figures 5, 6).
An alternating injection of balanced salt solution and air allows the graft to be unrolled and positioned on the posterior surface of the recipient stroma (Figure 6). The graft’s tendency to curl up with the endothelial cells to the outside is an important indicator that ensures that the graft is properly oriented during surgery. An air bubble is then injected to fill the anterior chamber and press the graft onto the posterior stromal surface (Figure 7). The air bubble is maintained for 30 minutes then 50% of it emptied.
Figure 6: Unrolling the graft in the anterior chamber.
Figure 7: Injecting an air bubble under the graft in order to press it onto the posterior stromal surface.
The advantages of DMEK
One major “theoretical” advantage of DMEK is the pure anatomical reconstruction, meaning that only the unhealthy tissue is replaced by identical healthy tissue. In practice, this solves the problem without creating another one. The corneal curvature is not changed and no additional stroma is added. DMEK restores the physical and functional characteristics of the cornea.
DMEK preserves eyeball integrity: the procedure involves performing a micro-incision (3 mm) that is similar to a cataract surgery incision. This causes little or no corneal denervation. In addition, the post-operative refraction is unchanged because the surgery is most often performed without sutures, resulting in little induced astigmatism.
There is no doubt that DMEK provides the best vision result and does so more quickly than any other type of graft: According to studies, more than 90% of eyes that undergo surgery achieve a postoperative AV of 5/10 or better and more than 80% of them achieve an AV of 8/10 or better. Rarely does the postoperative AV come out lower than the preoperative AV. Therefore DMEK is a very safe surgery.
Compared to other graft techniques, studies report a low rejection rate: less than 1% for DMEK, about 8% for DSAEK, and 20-30% for penetrating grafts.
Reversals are easy. The primary graft can be replaced if it fails.
There is no doubt that the surgical technique of choice for endothelial diseases today is the DMEK. The development of optical coherence tomography integrated to surgical microscopes now allows the direct viewing of the graft orientation and significantly simplifies the procedure (Figure 8, A and B).
Figure 8A: Direct intraoperative OCT showing an inverted graft with the endothelial cells facing the posterior stroma.
Figure 8B: Direct intraoperative OCT (Zeiss-Lumera microscope) of the same patient, confirming the proper orientation of the graft. Due to the elastic properties of Descemet's membrane the graft always curls up with the endothelial cells to the outside.
What Should I Know About My Surgery? Descemet Membrane Endothelial Keratoplasy: DMEK
The operation usually occurs under local / loco regional anesthesia. One night admission is sometime needed.
There is no pain during the surgery or after the surgery.
It’s primordial to keep a supine position during the first 5 hours after the surgery. It’s also important to sleep on the back the first 2 nights.
In case of intense pain and nausea, it’s important to have your eye checked by your doctor. Pain is usually caused by an increase in intra ocular pressure that might occur in the first hours after the surgery. Adequate treatment need to be started.
First day after the surgery:
An eye exam will be done and can assess graft positioning and adherence.
There is no pain. It’s possible to have dry eye and foreign body sensations.
Vision is still blurry.
First week after the surgery:
Dry eye and foreign body sensations will slowly decrease. You should respect your treatment (usually 4 to 6 times per day of steroids eyedrops).
Visual Acuity improves slowly.
An eye exam confirms the adherence of the graft. In case of peripheral graft detachment, (3 to 10% of the cases) and dependent on its severity, an air bubble is reintroduced in the eye. This can be done in the clinic and doesn’t need an operative room in most cases.
First month after the surgery:
Visual Acuity is improved and will continue to improve in the next few months.
Post-operative treatment need to be continued, more specifically, steroids eye drops should never be stopped without your surgeon authorization.