A marker in your eye can reveal if you are in danger of an early death, scientists say.
Their discovery means they can predict who may die within a decade before any clear signs of ill health.
Researchers say that the retina, tissue located in the back of the eye, can give clues about a person's health.
Damage to nerves and blood vessels in the retina can be an early warning sign of illness.
It is already known that factors such as high blood pressure, diabetes, smoking and poor diet are implicated in eye disorders such as macular degeneration.
New research suggests that if the retina ages faster than the person himself, it can predict an early death.
Researchers from China and Australia called this the "retinal age gap."
They tested their "eye-opening" theory on thousands of Britons.
Those with the largest retinal age differences of 10 years were up to 67 percent more likely to die during an 11-year study period.
"These results suggest that retinal age may be a clinically significant biomarker for aging," the authors wrote in the British Journal of Ophthalmology.
The retina offers a unique, accessible 'window' to evaluate underlying pathological processes of systemic vascular and neurological diseases associated with increased risk of mortality.
"This hypothesis is supported by previous studies that have suggested that retinal imaging includes information on cardiovascular risk factors, chronic kidney disease, and systemic biomarkers."
For their research, the researchers first checked that they were able to predict a person's age based solely on the retina.
They looked at the retinas of 19,200 British adults between the ages of 40 and 69.
A machine learning model was able to accurately predict the chronological age of the participant simply by looking at the retina within an interval of 3.5 years.
Thereafter, the retinal age gap and its association with death were assessed in approximately 36,000 volunteers over a period of 11 years.
During this time, 5 percent of people (1,871) died, most often from cancer.
All in the eyes
Those who died were more likely to have been "fast acting," meaning their retinas looked older than their true age, the study found.
For example, if the person's retina was one year older than their actual age, their risk of death for any cause increased by 2 percent over the next 11 years.
Their risk of death from a specific cause, other than cardiovascular disease or cancer, increased by 3 percent.
Large retinal age differences this year were significantly associated with between 49 and 67 percent higher risk of death, excluding cardiovascular disease or cancer.
The study was retrospective, meaning that the participants involved were already dead.
Researchers have yet to "predict" who may be in danger of an early grave by looking into their eyes now.
The new results add weight to "the hypothesis that the retina plays an important role in the aging process and is sensitive to the cumulative damage of aging, which increases the risk of mortality," the team said.
But a screening tool that helps identify those at risk of dying is just a twinkle in their eye for now.
Dr. Sunir Garg, a clinical spokeswoman for the American Academy of Ophthalmology who was not involved in the research, told CNN that clinicians do not currently have the means to pinpoint the age of a person's retina.
But the professor of ophthalmology at Wills Eye Hospital in Philadelphia added: "The really unique aspect of this paper is to use the difference in a patient's actual age compared to the age the computer thought a patient was to determine mortality.
“It's not something we thought was possible. Larger data sets on more diverse populations need to be performed.
"But this study highlights that simple, non-invasive eye tests can help us educate patients about their overall health."
Garg said it could hopefully mean patients can make changes to improve their health based on what their optician finds in their retina.
This story originally appeared on The Sun and has been reproduced here with permission.