MELBOURNE – Corneal nerve fiber length, measured using corneal confocal microscopy, is significantly reduced in individuals with type 1 diabetes who go on to develop diabetic neuropathy at 3 years, according to data from the longitudinal LANDMark study.
Researchers found that corneal nerve fibre length was significantly lower at baseline in individuals who developed neuropathy than in those who did not over the 3-year follow up (13.3 vs. 17.4 mm/mm2, respectively; P = 0.036).
Ms. Nicola Pritchard
Corneal nerve fiber length, which is a measure of amount of nerve tissue per unit area in the cornea, may be an useful, noninvasive adjunct to diabetic neuropathy screening, Nicola Pritchard, a researcher for the Institute of Health and Biomedical Innovation at Queensland University of Technology, Brisbane, suggested in her presentation of the results at the World Diabetes Congress.
"In animal models, we know that the dropout of nerves in the cornea actually does precede the dropout of nerves in the foot," Ms. Pritchard said in an interview.
"Our hope is that this technique will be useful to pick up very, very early signs of neuropathy, way before people are getting symptoms and before things develop to a stage where there’s damage," she said.
LANDMark (Longitudinal Assessment of Neuropathy in Diabetes Using Novel Ophthalmic Markers) is a 5-year observational study of 242 individuals with type 1 diabetes.
The 3-year analysis included data from 64 participants without baseline neuropathy, seven (11%) of whom had developed neuropathy by 3 years, as defined by the Toronto criteria.
Study participants undergo annual neuropathy assessments, including measurement of corneal nerve parameters using corneal confocal microscopy and measurements of corneal sensitivity using noncontact corneal esthesiometry.
The study showed that reduced peroneal conduction velocity and cold sensation and increased vibration threshold also were associated with development of diabetic neuropathy.
However, although corneal nerve fiber length was significantly reduced at baseline in individuals who developed neuropathy, compared with those who did not, at the 3-year mark there was no significant difference in corneal nerve fiber length between the two groups.
Ms. Pritchard said that it was unclear why the nerve fibre parameters improved over time, suggesting that perhaps the nerves were growing to fill in the gaps.
Nathan Efron, D.Sc., research leader of the LANDMark study, said corneal confocal microscopy had the potential to be a very simple screening technique for diabetic neuropathy that could be applied at the same time as patients come in for their annual fundus photographs.
"At the very least, it’s a viable alternative technique to the range of techniques neurologists and diabetic specialists already have at their disposal, but the potential advantage of this technique is that it might be a very early marker of diabetic neuropathy," said Dr. Efron, professor in the School of Optometry and Vision Science at Queensland University of Technology.
"We’re not there yet, but down the line, that’s where this all could come to, as long as we can get more firm data and validate it a bit better," he said.
There were no relevant conflicts of interest declared.