Regression analysis of corneal endothelium after nonmechanical penetratingkeratoplasty

Purpose: The corneal endothelial cell density is a crucial parameter for th e pump function and the transparency of grafts after penetrating keratoplas ty (PK). The purpose of this study was to assess corneal endothelial cell d ensity with different regression models after nonmechanical penetrating ker atoplasty and to check for differences between diagnoses and two different storage methods. Patients and Methods: Two-hundred ninety-six eyes (195 keratoconus, 101 Fuc hs' dystrophies, 148 each with short-term preserved and organ-cultured dono r corneas) of 268 patients were included in this prospective study. Donor a nd recipient trephination was performed using nonmechanical trephination te chnique with the excimer laser 193 nm along metal aperture masks from the e pithelial side. The time course of the endothelial cell density (specular m icroscope EM 1100, TOMEY, Erlangen) after PK was assessed. Endothelial cell density was first analyzed in a cross sectional manner at the 3, 6, 12, 18 and 24 months follow-up and, secondly in a longitudinal manner with linear , polynomial and exponential regression models in the sense of minimizing t he residuum (distance between observed and predicted endothelial cell count ). The mean donor postmortem time was 10.3+/-6.8 hours for short-term-prese rved and 19.6+/-9.5 hours for organ-cultured corneas (p<0.0001). The storag e time was 63+/-49 and 19+/-7 days (p<0.0001), respectively. Results: In a cross section, overall mean endothelial cell density decrease d from 2145+/-599 cells/mm(2) at the 3 months to 1751+/-605 cells/mm(2) at 2 years follow-up (p>0.05). Cell density did not differ significantly betwe en different diagnoses or storage methods at any postoperative stage. In a longitudinal section, the linear regression model estimated an annual decre ase of 214 cells/mm(2). In a polynomial model the decrease expressed by a t angent to the regression line at 24 months was 175 cells/mm(2). The exponen tial regression model yielded a relative decrease of 9.5% annualy. The so-c alled residuum as a measure for the validity of the regression model was ma ximal in the linear and minimal in the exponential estimate. With keratocon us and short-term preserved donor material the endothelial cell loss was le ss in the regression analysis. Conclusion: During the first two years after nonmechanical trephination in PK, a non-significant decrease in endothelial cell density was observed. Th e exponential regression model seems to be predestinated for analysis of th e time course of corneal endothelium in a longitudinal manner. The annual c ell loss ranged around 9.5% without significant differences between diagnos es and storage methods.