The corneal endothelium reflected: Studies on surgical damage tot the corneal endothelium and on endothelial specular microscopy

The endothelium is the innermost layer of the cornea. It is a mosaic of hexagonal cells that is only one cell thick. These endothelial cells actively maintain the corneal hydration equilibrium, and hence are very important for its transparency. However, they are vulnerable to trauma, disease, and intra-ocular surgery, because they have a very restricted capacity for cell division. In part II, studies are presented on the reliability of in-vivo examinations of the endothelium with a specific type of specular microscope. We found that after correct calibration and with adequate assessment methods, valid and reproducible measurements of the endothelial cell density (ECD) could be obtained. However, there is a systematic difference between specular microscopic ECDs and donor cornea ECDs that are measured with a different technique. This difference can only in part be explained by optical factors. In part III, in a clinical and an experimental study, no toxic effects on the endothelium of current common applications of the dye trypan blue, in cataract surgery and in eye banks on donor corneas, could be observed. However, caution is warranted, as higher concentrations or longer exposures were found to cause substantial toxicity. In part IV, endothelial cell loss patterns were investigated after selective transplantation of different parts of the cornea (deep anterior and posterior lamellar keratoplasty, DALK and PLK). After DALK, ECD-loss approached normal levels after an initial drop. When however in PLK a posterior lamella including the endothelium was transplanted, ECD-loss continued at an increased level for up to 7 years. The possible consequences of this result for graft survival were discussed.

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