**3. Effect of donor and eye-bank variables on endothelial cell density and graft quality**

Donor factors such as age, local and systemic diseases, cause of death, and traumatic damages or surgical procedures as well as the storage factors (mainly method of storing, time between death and preservation, and duration of tissue preservation) can influence the final quality of the corneas. The age of donor, time interval from enucleation to corneoscleral disc excision, and time interval in organ culture are the main variables influencing the quality of endothelium [18, 26, 27]. Gavrilov et al [28] reported that the rate of organ-cultured corneas which were inappropriate for PK as a result of inadequate endothelium increased from 13% in donors < 40 years to 32% in donors > 80 years. The Cornea Donor Study revealed a negative correlation between donor age and ECD [29]. Armitage et al [18] revealed that the age of donor and preservation time in organ culture were the main variables which could affect endothelial suitability for PK. The odd of ECD less than 2500 cells/mm² was increased with longer preservation time and increasing donor age. Increasing time interval from enucleation to corneoscleral disc excision also in‐ creased the likelihood of ECD less than 2500 cells/mm², but the overall impact was small and significant only for a time interval greater than 18 hours [18]. Grabska-Libereket al [27] found that the rating of the morphological state of corneas suitable for PK depended mostly on the time between death and preservation, donor's age, cause of death, and duration of preservation. The overall rating of tissues obtained in a very short time after death (to 5 hours) was higher (excellent and very good) compared with corneas removed 8–12 hours after the donor's death. An increasing percentage of endothelial cell loss was observed after 7 days of preservation independent of other factors [27]. One study found that initial ECD was lower and elimination for low ECD was more frequent in donors aged 85 years and above, compared to younger donors [26]. However, after storage in organ culture, very old corneas lost fewer endothelial cells than younger ones resulting in ECD which did not differ at the end of storage [26]. One study measured endothelial cell loss during preservation in organ culture [19]. The donor's gender, age, cause of death, and postmortem interval had no significant correlation with the percentage of endothelial cell loss. However, the preservation time demonstrated a significant correlation with a loss of 0.07% for each day of preservation [19].

Additionally, the combined effects of cause of death and donor age on ECD were evaluated. It was identified that chronic and long-lasting, severe diseases like cancer reduced ECD to a greater extent as compared to diseases causing a more rapid death. This negative impact of chronic diseases was aggravated by the general reduction in ECD observed with increasing age [30].
