A Biochemical and Histological Assessment of Postmortem Changes to the Eyes of Domestic Pigs: A Preliminary Study

Abstract

The Postmortem Interval (PMI) is the time from the death of an animal to its discovery. From a veterinary forensic standpoint, an accurate estimation of the PMI is of particular importance, especially with the observed increase in deaths of domestic and wild animals. A preliminary study was conducted using the eyes of domestic pigs. A biochemical analysis was conducted on the vitreous humor of the eye, whilst a histological analysis was conducted on the retina. The eyes were stored at +4 °C and changes were assessed at time intervals of 0, 12, 24, 48, and 120 h. The biochemical analysis during the PMI established a decrease in sodium, chlorine, and glucose concentrations, and a rise in potassium concentration. Accordingly, a simple linear regression showed a significant correlation between changes in concentrations of sodium (Na⁺), potassium (K⁺), chloride (Cl^-), and glucose, in relation to the PMI. The histological analysis showed evident morphological changes in the retina, which included homogenization of the rod and cone cells, pyknosis of the outer nuclear layer, homogenization of the outer plexiform layer, pyknosis of the inner nuclear layer, homogenization of the inner plexiform layer, and pyknosis of the nuclei of the ganglion layer of the retina.

Keywords: biochemistry; domestic pigs; electrolytes; histology; retina; vitreous of the eye.

Scheme 1

The results of the linear regression showing the correlation between sodium (Na⁺) concentrations (mmol/L) and PMI (hours); PMI-postmortem interval.

Scheme 2

The results of the linear regression showing the correlation between potassium (K⁺) concentrations (mmol/L) and PMI (hours); PMI-postmortem interval.

Scheme 3

The results of the linear regression showing the correlation between chloride (Cl⁻) concentrations (mmol/L) and PMI (hours); PMI-postmortem interval.

Scheme 4

The results of the linear regression showing the correlation between glucose concentrations (mmol/L) and PMI (hours); PMI-postmortem interval.

Figure 1

Representative figures showing the morphological changes in the retinas of domestic pigs at time intervals of 0 (A), 12 (B), 24 (C), 48 (D), and 120 (E) hours, at +4 °C. (A) There is no evidence of detachment of the nervous layer of the retina from the retinal pigment epithelium (RPE); the beginning of morphological changes is visible in the form of pyknosis of cell nuclei in the ganglion and inner nuclear layer. (B) An increase is visible in the number of pyknotic nuclei in the ganglion and the inner plexiform layer, with some pyknosis of cell nuclei in the outer plexiform layer, also with homogenization of the inner and outer retinal layer and the layer of cones and rods. (C) The progression of pyknosis in the outer nuclear layer, with pronounced homogenization of the inner and outer plexiform layer and the layer of cones and rods. (D) The progression and an increase in the number of pyknotic nuclei in the outer nuclear layer, with pronounced homogenization and a loss of integrity in the inner nuclear layer; (E) The progression of pyknotic changes with a loss of integrity in the ganglion layer, the inner and outer nuclear layer, and homogenization of the inner and outer plexiform layer and the layer of cones and rods. Measurement scale 50 μm, 400× magnification, Davidson’s fixative, H&E staining. Inserted figures: measurement scale 10 μm, 600× magnification, aqueous immersion, Davidson’s fixative, H&E staining.