Specifically, damage to the eyes' tiny blood vessels could be the first sign of heart disease, long before any other symptoms show up elsewhere, according to a study from Australia's University of Sydney and University of Melbourne, along with the National University of Singapore.

Reuters reports that people who had a type of eye damage known as retinopathy were more likely to die of heart disease over the next 12 years than those without it.

To reach this conclusion, the team studied the retinal photographs of 3,000 people, most of whom had type 2 diabetes. The photos were taken by the patients' doctors to determine if the diabetes had started to damage their eyes. Then the researchers checked the patients' medical records to determine who had died.

"Over 12 years, 353 participants (11.9 percent) had incident coronary heart disease-related deaths," said lead study author Gerald Liew of the University of Sydney. Those who had retinopathy were almost twice as likely to die of heart disease as people who didn't have it.

Startlingly, retinopathy increased the risk of heart disease as much as diabetes did, but people can use this as an early warning signal of artery damage and then work to lower their cholesterol and blood pressure.

The study findings were reported in the journal Heart.