ABSTRACT
Endothelial keratoplasty has replaced traditional penetrating keratoplasty for the treatment of corneal endothelial dysfunction. It offers faster, more predictable, stable visual recovery and low rejection rates while the surgery itself is less invasive. Descemet membrane endothelial keratoplasty (DMEK) is currently the gold standard for the treatment of Fuchs endothelial dystrophy, bullous keratopathy, and corneal edema after cataract surgery. Its favorable long-term outcomes are increasingly reported by large study groups. This review summarizes the current literature on new DMEK techniques, including size and shape modifications, new graft delivery techniques, and surgical pearls for challenging cases like eyes with glaucoma, glaucoma tubes, and failed penetrating keratoplasties.
Keywords:
Corneal transplantation, DMEK, hemi-DMEK, quarter-DMEK, DMEK in complicated cases
Introduction
Endothelial keratoplasty (EK) offers great advantages for the treatment of patients with endothelial dysfunction. It can be performed for Fuchs endothelial dystrophy, pseudophakic or aphakic bullous keratopathy, posterior polymorphous dystrophy, iridocorneal endothelial syndrome, or failed penetrating keratoplasty (PK). It provides more rapid visual recovery, lower rejection rates, better refractive outcomes, and greater structural integrity than traditional PK.1,2,3,4 Moreover, it provides a closed system that prevents PK’s most dreadful complication: intraoperative suprachoroidal hemorrhage.5,6
Modern EK techniques include mainly Descemet stripping automated EK (DSAEK), Descemet membrane EK (DMEK), and pre-Descemet EK (PDEK).7 In 2006, Melles1 first introduced DMEK that selectively replaces the Descemet membrane (DM) and endothelium, resulting in an anatomically accurate procedure. DMEK poses some technical challenges, such as the need for careful graft preparation and meticulous graft orientation techniques, which result in a steep learning curve.8 Despite this, DMEK has gained popularity in the last decade, and various modifications have been introduced that are gradually improving the surgical technique or donor preparation in challenging situations.9
As DMEK surgery became more popular, more information on its mid- and long-term results also became available. Recently, Birbal et al.10 reported outcomes for a cohort of 500 DMEK eyes with a 5-year graft survival probability of 0.90 and 82% of eyes achieving a best-corrected visual acuity (BCVA) of 20/25. The endothelial loss was 37% in the first 6 months, 40% at 1 year, and 55% at 5 years. Allograft rejection rates were as low as 1.7-2.8% compared to 5% in DSAEK and 14% in PK.10 Woo et al.5 compared DMEK survival at 5 years (97.4%) with DSAEK (76.4%) and PK (54.6%). Even after 10 years, pioneering DMEK surgery cases maintained excellent visual acuities with low rejection rates, further supporting DMEK as the gold standard treatment for corneal endothelial diseases.11
In this review, we will discuss new perspectives, various indications of DMEK, and elucidate the surgical steps of DMEK in challenging cases in light of recent scientific publications.
Conclusion
Data from the Eye Bank Association of America shows that between 2004 and 2014, the rate of PK decreased to half (from 95% to 42%) and was replaced by lamellar keratoplasty techniques (5% to 55%).85 The volume of EK procedures has been doubling every year since 2011.85
Fuchs endothelial dystrophy (47.7%) is the most common cause of endothelial failure, followed by corneal edema after cataract surgery (17.8%) that needs EK. DMEK offers significantly better graft survival of 98.7% in these eyes than DSAEK (78.4%) and PK (73.5%) in Fuchs endothelial dystrophy. PK results in eight-fold higher rejection rates compared to DMEK.5
For challenging cases like eyes with glaucoma, failed grafts, and vitrectomized eyes, DMEK still offers quick visual recovery, better graft survival, and lower rejection rates compared to traditional PK.
Although it has a learning curve, the literature on new techniques of DMEK is expanding tremendously, making it possible to perform DMEK in a variety of challenging situations.
This review summarized different approaches such as using different graft sizes (hemi-DMEK, quarter-DMEK), different graft folding techniques (endothelium-in delivery methods), new unfolding techniques (using a diaphragm in vitrectomized eyes), new positioning techniques (3/4-DMEK in eyes with glaucoma shunts), and double layers of DM in cases of failed PK. Hopefully, more standardized innovative modifications will enable cornea surgeons to treat endothelial dysfunction in almost any situation with confidence and great success.
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