Investigation of postmortem change in the human corneal epithelium via impression cytology

The corneal epithelium, which consists of superficial, intermediate, and basal layers, demonstrates layer-by-layer shedding with the prolongation of postmortem interval (PMI). This study aimed to evaluate postmortem changes in the corneal epithelium via impression cytology. Specimens were obtained from 134 cases of postmortem CT and/or autopsy, which were divided into 6 groups by PMI (6 h-14 days). The cells collected from the corneal surface using membrane filters were double-stained with antibodies against ZO-1 (expressing on superficial cells) and occludin (expressing on either superficial or intermediate cells) to identify them. With the prolongation of PMI, the percentage of ZO-1 (+)/occludin (+) cells decreased, whereas that of ZO-1 (-)/occludin (-) cells increased, demonstrating the shedding of the corneal epithelium. Meanwhile, ZO-1 (-)/occludin (+) cells initially exhibited an increase in percentage until 48 h and then became undetectable, suggesting a decline in stainability. Age, gender, and wet conditions did not have a significant effect on the number of ZO-1 (+)/occludin (+) or ZO-1 (-)/occludin (-) cells. The effects of ambient temperature and whether the eyelids were open or closed remain unclear due to a lack of data. A simple and noninvasive impression cytology may be applicable for diagnosis in forensic practice.