A simple eye test aids in the diagnosis of nerve damage associated with diabetes - the most common cause of foot ulcers and amputations.
Nerve fibre damage is typically assessed through invasive tests, including nerve and tissue biopsies.
Now, Nathan Efron at the Queensland University of Technology in Brisbane, Australia, and colleagues have developed a non-invasive alternative.
Diabetes affects peripheral nerves, but Efron suspected that it might also leave a signature in the cornea - the most densely innervated tissue in the body.
He has now shown this is true using a corneal confocal microscope: on average, the corneas of diabetic people with nerve damage have a lower density of nerve fibres, and nerves are shorter than in healthy controls.
Peripheral nerves lose their function in people with diabetes because excess glucose in the blood reduces blood flow to arms and legs.
"You are starving the nerve fibres of nutritious oxygen," New Scientist quoted Efron as saying.
Initially, it was thought that diabetes affected only these peripheral nerves. So to find that cranial nerves - such as those supplying the eye - were degenerating as well was a surprise, Efron says.
Efron's team has now developed a clinical test based on the findings.
Team member Rayaz Malik at the University of Manchester, UK, developed software that compares images of the central cornea with those taken from diabetics with varying degrees of nerve damage.
Efron says the test is now being used by several hospitals.
The work was presented at the Asia Pacific Academy of Ophthalmology Congress in Sydney, Australia, this week.