An eye exam can help determine the damage caused by diabetes

A glimpse in an eye might soon be enough to diagnose the nerve damage associated with diabetes. Up to 50 per cent of people with diabetes experience nerve damage, which in extreme cases leads to the loss of limb sensation, prompting the need for amputation.

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.

Nerve starvation

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," says Efron.

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. According to Efron, the test is now being used by several hospitals.

"It's a very interesting idea," says Hugh Taylor at the University of Melbourne, Australia. With the use of powerful microscopes, "the eye can be used as a fantastic window into the health of the body".

But he says that before the test is widely adopted, its results need to be compared against established measures, such as biopsies, to ensure they are as accurate.

The team presented the work at the Asia Pacific Academy of Ophthalmology Congress in Sydney, Australia, this week.

(New Scientist)
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