Dissection planes in endothelial keratoplasty.

To the Editor: We were interested to read the study by Yoeruek et al examining dissection planes and endothelial cell loss in donor preparation for endothelial keratoplasty (EK). In part of their study, they examined the dissection plane achieved when pneumatic dissection is used to create the donor graft in EK. In all the 14 samples examined, they found no stroma attached to the Descemet membrane (DM) on either light or electron microscopy, implying a complete separation of stroma and DM. We recently published a smaller study examining donor grafts after pneumatic dissection. We found residual stroma on all samples that was obvious on light microscopy and we thus did not proceed with electron microscopy. We are at a loss to explain the discrepancy between the results of these 2 studies. There are differences between our study and theirs as regards the methodology. In their study, the harvested grafts were put back into organ culture for a week as part of the endothelial cell count study. Ours were put immediately into formalin. We did conventional light microscopy using both hematoxylin and eosin and periodic-acid Schiff stains, whereas their “light microscopy” was done on semithin sections that usually guide electron microscopy. However, we doubt whether any of these differences would account for the differing results. The donor preparation technique they described is the same as what we used. We are interested to know if all their samples were prepared by the same surgeon. Perhaps, the surgeon preparing our samples inserted the needle further from the DM; however, from the photo in our study, it can be clearly seen that a “big bubble” has formed, indicating the correct end point was achieved. The authors suggest that their results are consistent with those seen in pneumodissection for deep anterior lamellar keratoplasty (DALK): “As shown for anterior lamellar keratoplasty, the separation of DM from the stroma produced by the Anwar bigbubble technique is reproducible, allowing a wide and complete exposure of the DM.” We would dispute this, with both an in vivo and an ex vivo study supporting the notion that some stroma routinely remains after bigbubble DALK. Anwar has also described a less common situation in which a completely different bubble forms in DALK, which appears like a water bubble in the anterior chamber. Our ex vivo studies suggest this represents complete separation of stroma and DM. It is possible that the authors achieved this different bubble type in all their cases. As already stated, they used the same technique we did so that it would seem unlikely they achieved this every time but we did not achieve it at all. Also, in DALK, we found that this bubble occurs infrequently and randomly. Yoeruek et al also mentioned that the results of their study are comparable with those of Busin et al. As mentioned in our article, we would encourage authors to ignore the study by Busin et al in terms of their interpretation of the dissection plane, as improper staining and magnification was used making it impossible for them to draw a conclusion in this regard. Yoeruek et al also looked at the dissection plane when manual peeling is used to harvest DM. They found bare DM in all 15 samples. To see if our results would again differ, we examined 3 samples by electron microscopy, looking at both the stromal side and the DM side. We also found a complete separation of DM and stroma, with no stroma attached to the DM, and no DM attached to stroma (Fig. 1). With the results of our study and the study of Yoeruek et al in disagreement in terms of the samples prepared by pneumodissection, we would encourage other authors to also examine the dissection plane achieved with pneumodissection. We would suggest samples be immediately placed in formalin to