All in the eyes: Clues to the year of your birth are locked away in the lens proteins of your eyes.
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BRISBANE: By analysing human eyes, forensic scientists have developed a new highly accurate carbon dating method for determining the age of corpses. They say it may aid the rapid identification of disaster victims.
The technique, which can be used up to three days after death, measures the amount of radioactive carbon in the lens proteins of a person's eye, to determine how long ago they were born.
"No other methods come within just one to two years of placing the year of birth accurately, like this," said one of the forensic scientists behind the method, Niels Lynnerup of the University of Copenhagen in Denmark.
Forensic scientists currently estimate the age of bodies by examining dental and skeletal remains. These methods are accurate to within three years in children but can be out by as much 10 years in adults.
Radioactive carbon
To develop the more accurate technique his team looked to variation in the amount of radioactive carbon in the atmosphere over time.
Widespread nuclear weapons testing between World War II and the 1960s led to an increase in the amount of the rare radioactive isotope, carbon-14, in the atmosphere. However, the level has been steadily decreasing since the 1960s, meaning that atmospheric levels have varied in a predictable way over that time.
Alongside the more common carbon-12, carbon-14 accumulates in human tissues and proteins, and the amount is proportional to atmospheric levels at the time the tissue was generated. Much of the crystallized protein found in the lenses of our eyes forms at birth, and is not replenished later in life.
"All our tissues have a constant turnover except dental enamel and the nucleus of the eye lens," said Lynnerup. "Thus the level of radiocarbon in the eye lens proteins is 'locked-in' corresponding to the levels at the time of formation of the lens, which is around birth."
Lynnerup and his team were therefore able to use particle accelerators to measure the ratio of the two isotopes of carbon in the lenses of 13 corpses and compare the proportions to known atmospheric levels over time. As they report in the journal PLoS ONE, they found the method could yield estimates of age accurate to within one to two years.
Medical applications
John Hilton, a former director of the Institute of Forensic Medicine in Sydney, Australia, said that the new method appears promising, but requires further testing.
"The extent of 'obliteration' in skull sutures [places where the bones of the skull join] has been used to estimate the age of unidentified bodies, but it is not as accurate as it was once thought," said Hilton, adding that no existing method to age corpses is precise.
Lynnerup added that using the method to measure the ratios of carbon isotopes in other tissue, such as cancerous tumours, could yield medical advances too: "Calculating the amount of carbon-14 in cancer tissues could perhaps tell us when the tissues formed, and this could further the understanding of cancer," he said.
