Descemet Endothelial Thickness Comparison Trial

The purpose of this study is to compare visual acuity outcomes of two types of endothelial keratoplasty: 1) Ultrathin Descemet's Stripping Endothelial Keratoplasty (DSAEK) or 2) Descemet's Membrane Endothelial Keratoplasty (DMEK). Half of the participants will be randomized to have DSAEK and the other half will have DMEK.

Corneal transplantation has evolved rapidly in recent years. Lamellar keratoplasty to replace diseased endothelium has led to faster recovery times, fewer complications, and better visual acuity outcomes. Currently, Descemet's Stripping Endothelial Keratoplasty (DSAEK) is the most common procedure because of its relative ease and good outcomes. Newer techniques such as Descemet's Membrane Endothelial Keratoplasty (DMEK), where Descemet's membrane alone is transplanted, has the potential to further improve visual acuity outcomes, produce fewer higher-order corneal aberrations and decrease rejection rates. However, donor preparation, increased intra-operative times, and problems with donor attachment in DMEK are all important limitations.

There are three potential mechanisms by which DMEK may provide better visual acuity outcomes than DSAEK; graft thickness, interface haze and corneal higher-order aberrations. Graft thickness has been correlated with best spectacle corrected visual acuity (BSCVA) outcomes among thinner grafts. One retrospective case series found that 71% of thin endothelial grafts (defined as <131μm) had BSCVA of 20/25 or better while only 50% of thick grafts (defined as ≥131) achieved this. In addition, higher-order aberrations, in particular of the posterior cornea, are increased after DSAEK. Theoretically, given the decreased tissue transplanted after DMEK this would be lessened, however, one retrospective series looking at higher order aberrations in DMEK compared with DSAEK found no difference in posterior aberrations of the central 4.0 mm zone between the two groups. Finally, interface haze may be increased in DSAEK and has been correlated with BSCVA.

Ultrathin DSAEK involves donor preparation with a deep microkeratome pass to produce donor grafts less than 100 um thick. This procedure may have similar results to DMEK but without the technical difficulties. Several large prospective series show similar visual outcome results and rates of immunologic rejection between ultrathin DSAEK and DMEK, however comparisons are difficult. This comparative effectiveness clinical trial could directly address these important issues. The investigators also anticipate that secondary analyses of the trial data will allow us to address several more.