Descemet Membrane Endothelial Keratoplasty in an Eye with Fuchs Endothelial Dystrophy and Keratoconus

Introduction

Keratoconus (KC) is commonly regarded as a bilateral, noninflammatory condition of ongoing corneal ectasia, and may be accompanied by other corneal pathologies, including Fuchs endothelial dystrophy (FED) (1). For patients afflicted with both disorders simultaneously, penetrating keratoplasty (PK) has traditionally been considered the standard of care (1). Recently, however, various techniques for selective endothelial replacement have been described, including Descemet membrane endothelial keratoplasty (DMEK) (2-3-4-5-6). Here, we describe our results with DMEK performed in an eye with coexisting moderate and stable KC and FED.

Case description

A 63-year-old white male presented complaining of poor vision bilaterally, measuring 20/50 (0.4) with best spectacle correction (BSCVA) in each eye. Clinical examination revealed inferior steepening and thinning of both corneas, along with confluent central guttae, central corneal edema, and grade-2 nuclear sclerotic cataracts. Interestingly, the patient's preoperative measured corneal values were somewhat more suggestive of a diagnosis of pellucid marginal degeneration (PMD), rather than KC, since the point of maximal corneal steepness and minimum corneal thickness were vertically displaced, and not co-incidental (Fig. 1). Specifically, maximum keratometry (Kmax) values and central corneal thicknesses were 57.0 diopters (D) and 55.5 D, and 591 µm and 558 µm in the right and left eyes, respectively, measured by Scheimpflug-based corneal tomography (Pentacam HR, Oculus). The posterior segment exams were unremarkable. Rigid contact lens over-refraction failed to improve the visual acuity in either eye. After discussing surgical options with the patient, the decision was made to proceed with a combined phacoemulsification, cataract extraction, intra-ocular lens implantation, and DMEK in the left eye. The operation was routinely performed and transpired without complication. Postoperatively, anterior segment optical coherence tomography (AS-OCT; Slit-lamp OCT, Heidelberg Engineering GmbH) demonstrated complete graft attachment.

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Fig. 1

Pre- and 1 year postoperative maps of anterior corneal curvature (A, B), posterior corneal elevation (C, D), pachymetry (E, F), and maximum densitometry.

By 3 months postoperatively, BSCVA had improved from 20/50 (0.4) to 20/25 (0.8) where it remained stable. The changes in corneal thickness, steepness, and haze (measured by densitometry values) are presented in Table I and displayed in Figure 1. Interestingly, after DMEK, and with the resolution of the patient's corneal edema, the corneal curvature, elevation, and pachymetry maps demonstrated the traditional KC pattern.

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TABLE I

Pre- and postoperative corneal parameters

	Preop	3 months postop	12 months postop
Best corrected visual acuity	20/50 (0.4)	20/25 (0.8)	20/25 (0.8)
Mean keratometry (Kmean, diopters)	49	48.1	48.3
Maximum keratometry (Kmax, diopters)	55.5	56.5	57
Total densitometry	27.5	25.1	20.6
CCT (µm)	558	490	483
TPT (µm)	523	420	442

CCT = central corneal thickness; TPT = thinnest point thickness.

Conclusion

For endothelial dysfunctions, DMEK has supplanted its predecessors (including PK) because the operation frequently entails superior visual results and fewer severe complications (2-3-4-5-6-7). Nevertheless, to our knowledge, the operation has never been described in patients with coexisting endothelial dysfunction and corneal ectasia. Because KC corneas possess an abnormal curvature, there is some concern that DMEK grafts would be predisposed to detachment. In their small study of the outcomes of Descemet stripping endothelial keratoplasty performed in KC eyes, Vira et al (8). reported a graft dislocation rate of 16.67%. In addition, because KC corneas frequently contain anterior stromal irregularities, there is added concern that the visual results following DMEK may be inferior to PK, which replaces the anterior corneal surface as well.

Here, however, we report a successful trial of DMEK in an eye with coexisting KC and FED. One unexpected finding was a steepening of the patient's cornea after surgery, which contradicted the usual anterior corneal surface stability typically seen after DMEK (5). It is also interesting that the patient's preoperative corneal diagnosis was somewhat confounded by the presence of corneal edema, which masked some of the characteristic features of KC, and suggested an alternative diagnosis (PMD). This also raises the question of whether other patients diagnosed with PMD may, instead, have a combined KC and FED. Further study is undoubtedly necessary, but this preliminary result suggests the possibility that isolated endothelial replacement with DMEK may be sufficient to achieve visual rehabilitation, even in those eyes with combined anterior and posterior corneal diseases, thereby sparing patients the need for full-thickness PK and the potential attendant complications.