Descemet-endothelial keratoplasty (DEK or DMEK, its popular acronym for Descemet's Membrane Endothelial Keratoplasty) consists of the selective replacement of the Descemet’s membrane complex (DM) and endothelium, without being accompanied by a deep stroma lamina as in the ELK (DSAEK). This complex has a normal thickness in the adult from 8 to 10 μm. The technique involves certain maneuvers described by Gerrit Melles, such as descemetorhexis, which consists of extracting only this layer leaving the corneal stroma intact and the introduction of a Descemet-endothelial graft through a small corneal incision^1-3.

Endothelium transplants (ELK/DSAEK and DEK/DMEK) are being imposed on penetrating keratoplasty (PK) for pathologies that affect this layer, because they provide a faster visual recovery, with less residual astigmatism, less aberrations, lower rejection rate and better final visual acuity (VA). The latter, however, has not yet been supported by studies with a high level of evidence⁴. Its main disadvantage is long-term endothelial loss. The DEK has the advantage over ELK that it is less expensive, since it does not need any sophisticated apparatus such as the microkeratome, and also produces a bigger and faster visual recovery, with fewer induced aberrations.

INDICATIONS

The indications of DEK will be those corneal pathologies in which the endothelial layer is affected without irreversibly compromising other structures. Among the most common pathologies that can be treated with this surgical technique are Fuchs' dystrophy (Figure 1) and pseudophakic edematous (bullous) keratopathy (Figure 2). Other indications include the traumatic detachment of DM, endothelial exhaustion after previous keratoplasty (penetrating or lamellar endothelial) (Figure 3), other endothelial dystrophies such as the posterior polymorphous (Figure 4) and congenital hereditary endothelial dystrophy, iridocorneal endothelial syndromes (Figure 5), congenital aniridia and certain forms of drug toxicity that specifically damage the endothelium (amantadine).

PATIENT SELECTION

The selection of the patient will depend on the experience of the surgeon. Being a technique with a prolonged learning curve^5,6, patients with integrity of anterior segment structures and complete vitreous are preferred for the first cases. The ideal cases would be a Fuchs' dystrophy or an edematous pseudophakic keratopathy not very evolved. In both pathologies, early surgery is recommended, before the corneal decompensation causes stromal fibrosis, which will lead to worse intraoperative visualization and worse final visual results.

In Fuchs' dystrophy, the time to indicate the surgery is usually in stage II of the disease, which is defined by a painless visual loss, more marked on awakening and which the patient usually describes as "haze". In slit-lamp examination, we may not yet see edema, and we will only see corpuscles or guttae in DM, more or less confluent, a variable degree of endothelial pigmentation and DM fibrosis in "beaten metal" (Figure 6). In stage III, the indication is no longer in doubt and it is the moment when epithelial and subepithelial cysts and vesicles appear, accompanied by different degrees of stromal edema and folds in DM (Figure 7). The clinical indicators to check the evolution of these patients will be pachymetry and visual acuity. Specular microscopy is not very helpful since the presence of guttae makes it difficult to recognize the endothelial cells and the comparison between consecutive studies.

More complex cases such as vitrectomized⁷, aphakic or phakic eyes, with anterior chamber (AC) intraocular lens (IOL) or extensive iris defects, lack of compartmentalization between chambers⁸, narrow AC, extensive anterior synechiae, previous unsuccessful grafts, glaucoma surgery with AC implants or advanced cases with stromal opacity are not good candidates for this technique, at least at the beginning of the learning, and another posterior lamellar technique such as ELK (DSAEK) or PK will be preferred. The more unstructured the anterior segment is, the more the complications increase (scheme 1).

PREPARATION OF THE PATIENT

In addition to routine studies to be performed on all patients with ocular pathology such as VA, refraction, slit lamp examination, tonometry and fundus, in patients who are going to be subjected to a selective transplant of DM-endothelium (DEK) we add studies of topography, pachymetry, endothelial microscopy and OCT tomography of the anterior segment. These tests will help us to better understand the condition of the cornea and neighboring structures. Although specular microscopy is the basic tool to study the endothelium clinically, these cases usually have a very destructured endothelial map and the usefulness of this test is limited here (Figure 8). Confocal microscopy can achieve in these cases more informative images of the endothelium than the specular one.

The anterior segment OCT will give us a lot of information about the anterior structures of the eye. We are interested in knowing the corneal diameters, the depth of the AC and the state of the angle. In the case of treating a patient with a previous PK, it is very useful to know the existence of internal steps in the donor-recipient union, which can condition the adherence of the new graft. In these cases, we recommend that the donor disc be somewhat smaller than the old graft, so that it remains inside these steps (Figure 9).

An important fact in pseudophakic patients is the type of implanted IOL. If the IOL is hydrophilic, we should avoid prolonged contact with the air/gas in the early postoperative period of the DEK, since there is a risk of calcification of its surface^9-11 (Figure 10). We should also check if there is a posterior capsulotomy. In this case we will have to be more careful in the maneuvers, since a residual vitreous bridle could compromise the adherence of the graft (Figure 11).

In cases with edematous keratopathy and AC IOL we can consider a DEK, although it is not ideal for a surgeon with little experience. If we decide to try it, we must measure the distance from the anterior side of the IOL to the endothelium, which should be >2.5 mm, and check that the IOL is stable. Even so, the rate of detachments of DEK is high in this situation¹² (Figure 12).

Another case that provokes more debate is the presence of corneal decompensation in phakic patients, in particular if only corneal surgery can be done or the lens should be removed. In addition, in the second case, it is necessary to decide between performing both surgeries sequentially or simultaneously. In view of the publications, the following can be recommended:

In patients under 50 years: only perform corneal surgery, since the formation of cataracts after a DEK is rare^13-15.

In people older than 50 years: perform corneal and crystalline surgery. In this case the debate is whether to do them at the same time or deferred. In less experienced surgeons, combined surgery is associated with a higher rate of complications (especially the rate of graft detachments). In these cases, it would be advisable to separate both surgeries even if only a few days. In this way, the surgical approach is easier, since for DEK it is more comfortable to work with an already pseudophakic eye. However, series with a representative number of patients show that simultaneous combined surgery has no more complications than the delayed one in expert hands.

The rejection rate after DEK is lower than after ELK and much lower than after PK. Therefore, in patients with Fuchs' dystrophy and significant bilateral involvement, we can consider bilateral surgery with little difference in time between both eyes without involving a greater risk of rejection¹⁷.

One of the most fearsome complications in the immediate postoperative period is the appearance of acute glaucoma due to angle closure related to the presence of air in AC. Its frequency varies between 0% and 15% or 4% according to some series^5,18 (Figure 13). To avoid this, post-operative measures such as dilating the pupil and keeping the patient in the supine position or removing some of the air in the early postoperative period, are recommended. We prefer to perform a pre- or intraoperative iridotomy in the lower sector. In less evolved cases, it is possible to practice it with Nd: YAG laser before surgery (Figure 14). If the corneal transparency is insufficient, we will have to do it during the procedure.