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Specimen types , Vitreous humour

المؤلف:  Sue Jickells , Adam Negrusz (Editors)

المصدر:  Clarkes Analytical Forensic Toxicology

الجزء والصفحة:  194-195

2026-10-11

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Vitreous humour

Vitreous humour has been used for many years as the preferred specimen for postmortem confirmation of the ingestion of ethanol, since post mortem formation of ethanol (which has been demonstrated in blood and tissues) does not occur to any significant extent in vitreous humour. Even in the presence of elevated concentrations of glucose, fermentation does not occur because the interior of the eye is a sterile medium until the most advanced stages of decomposition. For this reason, vitreous humour is particularly useful for ethanol estimation in decomposing bodies. Vitreous humour has also been used increasingly for the measurement of drugs. For example, digoxin concentrations increase markedly in postmortem cardiac blood, but do not increase significantly in vitreous humour (Vorpahl and Coe 1978). Accordingly, vitreous digoxin concentrations give a better indication of perimortem concentrations than do those in heart blood. It has also been shown that monoacetylmorphine and cocaine may be more stable in vitreous humour than in blood (Lin et al. 1997). This presumably results from the relative lack of esterases in the eye as compared with blood. The main disadvantage of vitreous humour is its relatively small volume about 3 mL in each eye. Another disadvantage is that there is relatively little information in the literature on the concentrations expected after therapeutic doses for most drugs. While the vitreous: blood ratio for some drugs is close to unity, it is considerably less than unity for many drugs. The concentrations of highly lipid-soluble drugs, such as benzodiazepines, are relatively low in vitreous humour compared with whole blood; concentrations of highly protein bound drugs, such as the tricyclic antidepressants, also tend to be much lower (Evenson and Engstrand 1989; Scott and Oliver 2001). The use of vitreous humour is therefore limited by the volume available, and the difficulty of interpretation of the results for many drugs.