The biochemistry of the vitreous humour in estimating the post-mortem interval—a review of the literature, and use in forensic practice in Galicia (northwestern Spain)

The K + and hypoxanthine (Hx) concentrations of the vitreous humour (VH) rise gradually after death, providing a means of estimating the post-mortem interval (PMI). The correlation between these analytes and the PMI is good since the vitreous chamber is partially isolated from autolytic events occurring elsewhere; the [K +] and [Hx] recorded is thus the result of changes within the eye. The present work provides a systematic review, following PRISMA recommendations, of 36 articles (3 reviews and 33 retrospective cohort studies) discussing the many procedures and regression models that have been developed for improving PMI estimates involving VH analytes. The results of a descriptive study are also provided, highlighting the causes and distribution of mortality as registered in medico-legal autopsies performed in 2019 in Galicia (northwestern Spain), and revealing the use of these PMI estimation methods in real forensic practice. Great heterogeneity was detected in the collection of VH samples, the treatments to which they were subjected before examination, and in their conservation and analysis. A lack of reproducibility in the analytical methods employed to estimate [K +] and [Hx] was noted, as well as an absence of external validation for most of the regression formulae used to determine the PMI from analyte values. The use of methods based on high-performance liquid chromatography, focal electrophoresis, or thermogravimetric/chemometric procedures might solve the problems encountered with traditional analytical techniques, offering reliable results more quickly and effectively (even when samples are contaminated). This study recommends using flexible multiple regression models that combine physical and chemical variables, and that population databases be constructed so that models can be properly validated.