Vitreous potassium is used forensically to estimate postmortem interval (PMI). Which statement BEST describes the mechanism and reliability of this method?
- A Potassium diffuses into vitreous at a constant rate, giving a PMI estimate reliable up to 10 days
- B Potassium rises at approximately 0.14–0.17 mmol/L/hour due to retinal cell autolysis, with PMI validity limited to roughly 72–100 hours ✓
- C Potassium rises due to active transport by the ciliary body and peaks at 48 hours
- D Vitreous potassium remains stable for 7 days and is unaffected by temperature
Correct answer: B. Potassium rises at approximately 0.14–0.17 mmol/L/hour due to retinal cell autolysis, with PMI validity limited to roughly 72–100 hours
Explanation
After death, retinal and vitreous cells undergo autolysis releasing intracellular potassium into the vitreous humour. The rate of rise is approximately 0.14–0.17 mmol/L per hour (Sturner's regression equation), yielding the formula: PMI (hours) = (vitreous K+ in mmol/L − 7.14) / 0.14. The method is most reliable within the first 72–100 hours; beyond this, variability increases substantially due to temperature effects. Active transport ceases at death, so option C is incorrect.
Reference: The Essentials of Forensic Medicine and Toxicology (Narayan Reddy), 34th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.