[Temporal pattern of postmortem color changes in the pupil region of the cornea in rabbits]

To explore the temporal pattern of postmortem color changes in the pupil region of the cornea for noninvasive estimation of the postmortem interval (PMI).

Two rabbit models of air embolism and drowning were established in a dark room at a temperature of 20 ℃ with a relative humidity of 30%. The corneal images of the rabbits were acquired using a digital camera at two-hour intervals within 72 h after death. The pupil region on the corneal images was segmented using computer image processing technique (MATLAB), and the parameters of 6 image color features (RGBHSV) were extracted. Regression analysis was used to analyze the relationship between these parameters and the PMI, and the effects of different death causes on the changes of the corneal color features were also assessed.

Within 72 h after death from different causes, the R, G and B values of the pupil region on the corneal images all tended to increase with the PMI, showing a good fitting with the PMI (P < 0.01). No significant correlation was found between the values of H, S and V and the PMI (P>0.05). The R, G and B values in the pupil region on the corneal images showed consistent variation trends after death from the two causes, and their correlations with PMI were also similar. The measured values of R, G and B in air embolism group were greater than those in the drowning group.

The postmortem color changes of the pupil region on corneal images follow an identifiable temporal pattern and can vary across different causes of death. The regression equations established in this study provide references for non-invasive and objective estimation of the PMI.