Role of vitreous humor biochemistry in forensic pathology
Abstract
Vitreous humor is a fluid that is relatively well protected from postmortem degradation and contamination. Due to its postmortem stability, vitreous humor has high utility in forensic pathology. Vitreous humor biochemical constituents, especially potassium, have been widely used in the postmortem interval (PMI) estimations. The time dependant rise of vitreous potassium levels in the postmortem period has been considered to be helpful in PMI determinations. The relative stability of vitreous biochemistry is useful in assessing the antemortem metabolic status and in predicting the antemortem serum biochemistry of an individual. However, the validity of vitreous biochemistry in forensic applications has been questioned in light of the reported concentration differences of various biochemical constituents in the same pair of eyes at identical PMI. This study hypothesized that the concentration of vitreous biochemical constituents in the same pair of eyes change at the same rate and this change that occurs in a time dependent fashion may be utilized in accurately estimating the PMI. It was further hypothesized that postmortem vitreous humor biochemistry closely mimics antemortem serum biochemistry and may be a useful aid in establishing a postmortem diagnoses of hyperglycemia.
To test these hypotheses, vitreous humor samples were collected from a total of 103 autopsies (Female, 35 and Male, 68; Mean Age ± SD, 60.6 ± 17.6) conducted at Royal University Hospital morgue between January 2003 to February 2005. In 61 of these subjects, the precise time of death was known. Right and left eye vitreous humor samples were collected separately through a scleral puncture at the lateral canthus. Most of the biochemical analyses were carried out immediately post-extraction. After centrifugation, the supernatant of the fluid were analyzed for sodium, potassium, chloride, calcium, magnesium, urea, creatinine, glucose and lactate on an LX-20 Analyzer (Beckman-Coulter). Osmolality was measured on an Osmometer model 3900 (Advanced Instruments Inc.). Vitreous humor hypoxanthine and xanthine were analyzed using a colorimetric method (Amplex® Red Xanthine/ Xanthine Oxidase Assay Kit, Molecular Probes Inc.). Vitreous humor lipid hydroperoxides were measured using the Ferrous Oxidation in Xylenol Orange assay version 2 (FOX 2). The data was statistically analyzed by paired t-test, linear regression analysis and Mann-Whitney test using Statistical Package for Social Sciences (SPSS) for Windows™ version 13.0.
The results of this study indicated that there were no significant between-eye differences for all of the vitreous biochemical constituents that were studied. It was observed that there was a significant correlation between vitreous potassium (R, 0.731; P,