Artificial Anterior Chamber Pressure and Corneal Thinning Rate in UT-DSAEK
We read with great interest the article by Dimitry et al1 in which they describe and assess the surgical technique to achieve ultrathin Descemet stripping automated endothelial keratoplasty (UT-DSAEK) using a single pass with a 350-mm microkeratome head (Moria SA, Antony, France). We agree on the efficacy and advantages of single pass to obtain UT-DSAEK and the benefits of deturgescence. We have also previously reported the procedure to obtain UT-DSAEK with a single pass using a simple method of controlling artificial anterior chamber pressure and drying the corneal surface.2,3 Although we agree with the results of this article, we have several points to highlight that could significantly improve the reproducibility of this technique and allow readers to follow a standardized procedure while preparing an UT-DSAEK graft.
The authors mention that the use of a single cutting head (350 μm) in a cornea between 520 and 540 μm is enough to achieve a targeted donor button thickness of <100 μm. In our experience, the chosen settings of artificial anterior chamber pressure can play a crucial role in preparation of an ultrathin DSAEK graft, and the results may vary dramatically.2,4 There is, however, limited discussion of the thinning rate and the normogram used, which are important parameters in this setting to allow application of the presented results by clinicians. In fact, the authors mention that the corneas were thinned at 2 phases: (1) deturgescence and (2) a theater light on DSAEK (point (2) was for eyes that did not undergo simultaneous cataract surgery); however, in both of these phases, the thinning rate and the nomogram used are not quantified. There is a necessity to further thin down the tissue even after deturgescence.
The authors chose a pressure of 65 mm Hg for achieving the thinnest targeted stromal bed thickness. The rationale of this pressure should be specified, considering that other pressures (optimum/standardized) to cut the graft could also be useful. Standardizing the pressure rate is also important because it directly affects the endothelial cells. As reported in the literature, UT-DSAEK grafts are associated with faster visual recovery compared with DSAEK and a postoperative visual acuity comparable with Descemet membrane endothelial keratoplasty over time (later than 2 years).5 Inverse association between the quantity of transplanted stromal tissue and the visual outcome has also been reported in pre-descemetic deep anterior lamellar keratoplasty.6–8
Thinning of the donor cornea to a certain precut target thickness is equally important along with the graft size. We propose peripheral manual dissection in the case of a large graft of >8.5 mm to avoid the wedge profile and the thicker peripheral cornea.
We have observed a decreased rate of intra- and peri-operative complications when using ultrathin large-diameter (9.5 mm) DSAEK grafts. Graft diameter is an important variable associated with increased graft survival,4 considering basic calculation of increased number of cells, and the techniques, mainly the pressure and the thinning rate, used to produce ultrathin DSAEK need to ensure that they are also applicable to producing 9.5-mm graft diameters. Therefore, we believe that it is important to highlight the parameters such as graft thinning and pressure while cutting specifically for the readers to reproduce the results.