Do we overestimate the endothelial cell "loss" after descemet membrane endothelial keratoplasty?

Purpose: To evaluate how corneal deturgescence after Descemet membrane endothelial keratoplasty (DMEK) influences the posterior corneal surface area and the endothelial cell density (ECD) measurements.

Materials And Methods: A mathematical model was formulated to estimate the increase in posterior corneal surface area associated with postoperative corneal deturgescence and its effect on ECD measurements. Important input parameter for the model was the change in pachymetry from 1 h to 6 months after surgery. To this end, the clinical records of 25 patients (25 eyes) who underwent DMEK were reviewed retrospectively and the central corneal thickness (CCT) measurements taken after 1 h, 1 month, 3 months and 6 months were noted. ECD measurements before surgery and at 1, 3 and 6 months after surgery were also recorded and decrease in pachymetry and ECD loss were calculated.

Results: The average decrease in CCT due to corneal deturgescence was 267 µm (±39 µm), which corresponds to an 8.6% increase in total posterior corneal surface area, as calculated using our mathematical model. The stretching of the endothelial cell layer associated with this increase of posterior corneal surface area may result in an apparent endothelial cell "loss". This might account for approximately 25% of the observed average ECD decrease of 34% (±17%).

Conclusions: The observed decrease in ECD within the first 6 months after DMEK may overestimate the actual loss of endothelial cells by about 8% due to increased posterior corneal surface area associated with postoperative corneal deturgescence.