Tear test sheds light on diabetic condition

Tear testing could replace skin biopsies in detecting diabetic peripheral neuropathy, a debilitating complication affecting almost 50 per cent of diabetics.

A new study from UNSW Sydney is claimed to be the first to show that peripheral nerve damage, often the earliest sign of the type 1 diabetic peripheral neuropathy, can be traced in tear film.

“We found that people with the condition, which can result in recurring ulcers of the feet and in severe cases require amputation, have reduced levels of a protein known as ‘substance P’ in their tear film,” study senior author Dr Maria Markoulli said.

“About 119,000 Australians have type 1 diabetes. In the future, they may be able to have a quick tear sample collected, either at their optometrist, pharmacy, GP or endocrinologist, and be told whether they’re at risk.”

Peripheral neuropathy is the most common complication of diabetes, occurring when chronically high blood sugar damages the nerves connecting the brain and spinal cord to the rest of the body. Symptoms include pain, numbness, imbalance, weakness, pins and needles, and recurring foot ulcers.

While nerve damage cannot be reversed, early detection can help patients better manage the condition and prevent further complications. However, current early testing options are limited to invasive examinations, such as skin biopsies.

“Peripheral neuropathy is notoriously difficult to detect early on and requires specialty training,” Dr Markoulli said.

“What we’re proposing is something that will be done quickly, non-invasively, and potentially could even be done by a non-specialist.”

The researchers tested the concentration of two proteins (neuropeptides) in the tear film of people with type 1 and type 2 diabetes, compared with control groups. The study involved almost 100 participants.

While the researchers found that those with type 1 diabetic peripheral neuropathy had less ‘substance P’ protein in their tear film, the results didn’t suggest that those with type 2 diabetes have the same biomarkers.

“This is perhaps because these diseases have different pathologies and risk factors,” study lead author Shyam Sunder Tummanapalli said.

While the results are promising for those with type 1 diabetes, further study is required before tear testing becomes available clinically. In particular, the researchers hope to study substance P loss over time according to varying severities of peripheral neuropathy.

Dr Markoulli is planning to expand the study to determine specific changes in type 2 diabetes.

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