“Television has brought back murder into the home -where it belongs.” -Alfred Hitchcock
My friend looked up from her book. “Is it true that potassium levels rise in the vitreous after death?” she asked.
I had to admit having never pondered the question. As an ophthalmologist, I have dealt only with the living for the past few decades. The closest exception would be a resident after being forced to listen to me lecture for an hour. But at least the resident rendered moribund by 60 minutes of PowerPoint slides has a reasonable chance of recovering.
In my friend’s novel, a corpse and a syringe containing potassium are discovered. When the dead woman is found to have a high level of potassium in her vitreous cavity, the veterinarian husband (naturally!) is suspected of dispatching the victim via an injection of potassium. But a forensic expert comes to the rescue by revealing that increasing concentration of potassium in the vitreous is a routine finding after death and not proof of murder.
A review of forensic pathology literature reveals that the author of this novel did her homework. The composition of electrolytes in post-mortem vitreous humor has been extensively studied and use of this fluid for determining the cause of death has become commonplace, including testing glucose levels in diabetes-related deaths as well as alcohol and drug-related fatalities.
Vitreous is a favorite fluid for forensic pathologists because it is easily accessible, only slightly influenced by sudden fluctuations in blood chemistry, and its composition is more stable and less affected by post-mortem changes than most other bodily fluids (such as CSF or blood).
Vitreous is the most investigated body fluid for estimation of the post-mortem interval (PMI)-the time elapsed between death of a person and the time of the autopsy. Chemical changes in the constituent electrolytes after death (potassium, sodium, chloride, calcium, phosphate, urea, creatinine, and lactate) are used to estimate the PMI and help convict the murderer (either the butler or the husband).
The relationship between PMI and potassium concentration in the vitreous was first described in 1962. Potassium diffuses postmortem from the retina and, to a lesser extent, the crystalline lens into the vitreous. Serum and CSF potassium rises rapidly after death, but vitreous potassium levels rise gradually and linearly in the postmortem period.
In persons dying of drug over dosage, measuring drug levels in the vitreous is helpful because the cocaine (for example) concentration in the vitreous is strongly correlated with levels in whole blood and in brain tissue.
After looking at a few dozen articles on this topic of analyzing vitreous after death, I gave up looking for articles that might explore whether prior vitrectomy surgery alters the value of testing this fluid after death. It seems to me reasonable to suspect that an eye with retinal disease and prior vitreous surgery might have a different chemistry than the normal eye.
Thanks to the extensive body of published research, we can draw the following conclusions:
J Clin Exp Pathol. 2015;5:1.
J Forensic Leg Med. 2013;20:143-145.