Role of corneal tomography in determining the outcomes of descemet membrane endothelial keratoplasty in fuchs endothelial corneal dystrophy

Dear Editor, The endothelial dysfunction in Fuchs endothelial corneal dystrophy (FECD) leads to the gradual onset of corneal edema with a diminution of vision which in later stages may lead to bullae formation and subepithelial fibrosis.[1] Early diagnosis aims to avoid the chronicity of these corneal changes, and their incomplete resolution following endothelial keratoplasty (EK) Scheimpflug imaging has emerged to be an additional objective method to diagnose early edema in FECD and categorize the disease severity in FECD.[2,3] Recently, Patel et al. proposed Scheimpflug imaging classification of FECD that categorizes the disease entity into three categories: (1) clinically obvious edema, (2) subclinical corneal edema, or (3) no edema, independent of central corneal thickness. They found that the presence of irregular isopachs, displacement of the thinnest point of the cornea, and focal posterior surface depression was present in eyes with subclinical corneal edema.[3] In our retrospective observational study, we determined the feasibility and application of this Scheimpflug-based grading to detect corneal changes following Descemet membrane endothelial keratoplasty (DMEK) in FECD patients. The three specific features studied and compared in our study were as follows: Loss of regular isopachs Displacement of the thinnest point of the cornea Focal posterior depression. Nine out of 10 eyes had successful DMEK with a functional graft at one year. One patient had a failed EK following graft rejection. The preoperative corneal thickness at the pupillary center using Scheimpflug imaging (Pentacam Scheimpflug analyzer, Oculus Optikgerate GmbH, Wetzlar, Germany) was 605.33 ± 35.25µ (560–667µ), while the post-operative thickness was 499.11 ± 19.97µ (465–521µ) (P = 0.0001). Visual acuity improved in all eyes following DMEK from 1.18 ± 0.34 to 0.24 ± 0.31 (P = 0.0005). Mean preoperative and post-operative astigmatism of the front surface were 3.66 ± 3.06D and 3.28 ± 2.56D, respectively. Mean preoperative and post-operative astigmatism of the back surface were 2.8 ± 2.95D and 0.75 ± 0.47D, respectively (P = 0.004). There was a significant change in the astigmatism of the back surface of the cornea following DMEK; however, the front surface did not show any significant change. In the anterior curvature map, there was a decrease in mean astigmatism and skewing of the radial axis. In the pachymetry map, it was noted that there was a steady displacement of the thinnest pachymetry point towards the center or inferotemporal region following DMEK which has been represented as a scatter plot [Fig. 1]. This has also been represented in the pachymetry map [Fig. 2a and b]. Mean posterior depression, in the posterior elevation map, was reduced from − 238.75 ± 179.86 preoperatively to − 72.62 ± 40.58 postoperatively (P = 0.002). The tomographic changes are summarized in Table 1.Figure 1: Scatter plot representing the comparison of the thinnest pachymetry point displacement between the preoperative (blue dots) and post-operative period (orange dots), and the circle represents the central 4 mm of the pachymetry mapFigure 2: (a) Preoperative loss of regular isopachs indicated by a black arrow and displacement of the thinnest point of the cornea outside the inferotemporal quadrant on the pachymetry map indicated by the red arrow. (b) Post-operative regularization of the isopachs indicated by a black arrow and displacement of the thinnest point of the cornea on the pachymetry map toward the center indicated by a red arrowTable 1: Tabulated results of preoperative and post-operative corneal tomographic parametersIn one of the patients, we noted a reversal of these findings following an episode of graft rejection. The graft eventually failed, and the patient required repeat DMEK. In our study, we have shown the feasibility of using Scheimpflug imaging parameters such as tomographic pachymetry, posterior corneal depression, loss of regular isopachs, and displacement of the thinnest point of the cornea, in determining the outcomes of EK in FECD cases. Tomographic imaging provides a functional assessment of corneal endothelial health and enables an objective assessment of the disease progression. Posterior elevation and pachymetry map changes can detect subclinical disease, facilitating early surgical intervention and predicting visual outcomes with or without cataract surgery.[4] Santana et al.[5] evaluated Scheimpflug parameters of eyes with FECD to correlate the influence of DMEK on FECD severity and the presence of subclinical edema. In their study of the eyes without preoperative edema, most of the parameters reversed back to the normal level compared to those with subclinical edema. They have also concluded that corneal tomography might be best suited for objective grading of disease severity to aid in surgical decision-making. On pachymetry maps, a significant central displacement of the thinnest pachymetry point was noted along with regularization of isopachs, which points toward the improvement in corneal edema and signifies a functional status of the graft. The posterior depression which was noted in the preoperative period disappeared following a successful EK. In one of our patients, who showed the above changes, we noted a reversal of all these parameters to the preoperative stage after an episode of graft rejection. In patients of EK on serial follow-ups, changes can be monitored to look for early changes of graft failure. However, our study included a smaller sample size without a control arm (patients of FECD who did not undergo EK). We also included only patients with FECD as we intended to study the resolution of tomographic changes following EK. It would be interesting to explore the tomographic changes in other causes with corneal decompensation with a larger sample size. Financial support and sponsorship: Nil. Conflicts of interest: There are no conflicts of interest.