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Dead men's eyes tell age old tales


Matching the carbon-14 content of someone's eye lens with past levels in the atmosphere can tell forensic scientists how old someone was when they died (Source: iStockphoto)

A way to decipher a person's age by looking into the lens of the eye could help forensic scientists identify bodies, Danish researchers say.

Their technique uses radiocarbon dating to measure special proteins known as lens crystallines that develop around birth and remain unchanged for most of the rest of our lives.

They are the only part of the body apart from teeth that do so.

The researchers correctly identified the ages of 13 people within one-and-a-half years by analysing the carbon isotope carbon-14 trapped inside the crystallines, they report in the journal PLoS ONE.

"In forensics we are always looking for ways to identify deceased persons," says Associate Professor Niels Lynnerup, a forensic scientist at the University of Copenhagen, who led the study.

"We found with this method you can determine almost to the year, the year of birth."

Scientists have long used radiocarbon to date archaeological finds. More recently, researchers have applied the technique to tooth enamel to tell the age of people who have recently died, Lynnerup says.

The technique used in the lens analysis is based on the sudden increase in atmospheric carbon-14 beginning in the 1950s until a test ban a few years later when the Soviet Union and the US began testing nuclear bombs.

These experiments more than doubled the amount of atmospheric carbon-14, which gradually began to decline towards normal levels after the ban, Lynnerup says.

Scientists have recorded these levels annually, giving the Danish team a benchmark to date a person's birth by matching the corresponding year in which the carbon-14 atmospheric content was as high as in the person's eye lens.

The researchers also say their technique could one day help scientists in other fields to date proteins and other molecules in the body to determine when cancer tissues or cells developed.

The new method offers certain advantages.

For one, lifting up the eyelid to extract the lens is often much easier then extracting part of the tooth needed for an accurate reading, Lynnerup says.

The downside is that a lens disappears after a few days as the body decays while a tooth provides a sample scientists can use even after a few years, he says.

Tags: eyes, chemistry, forensic-science