Diabetic ocular nerve damage may be going undetected

The long-held progression of diabetic eye disease – starting with retinopathy and progressing to neuropathy – and therefore, its treatment, has been upended by a new study.

University of Iowa scientists, with their colleagues at the Academic Medical Centre in Amsterdam, have spotted ocular nerve damage in diabetic patients with no history of retinal blood vessel problems.

Until now, practitioners have thought that preventing retinopathy would prevent neuropathy, and so they concentrated on detecting and treating the former to prevent blindness.

Study senior author, Dr Michael Abramoff, told OT that scientists had started to rethink this relationship, bolstered by researchers at the University of Manchester finding corneal nerve damage in people with diabetes, despite a normal cornea having no blood vessels.

He explained: “There was an example that neurodegeneration in the eye can occur without vasculopathy [blood vessel damage], and thus we set up a series of prospective studies.”

The study tracked 45 people with diabetes, but little to no history of diabetic retinopathy, over four years. Yet this group had a “significant, progressive” loss in their nerve fibre and ganglion cells, Dr Abramoff said.

“Even people with diabetes who never get retinopathy can still develop this damage, and after many years, the damage may be as severe as in glaucoma,” he added.

The results of the 45-person study, published in the journal PNAS, have also been confirmed by retinal thinning in donor eye tissue and in animal model trials using mice.

These outcomes indicate that vascular damage does not cause nerve damage in the retina, he said. Therefore, either nerve damage causes retinal blood vessel damage or diabetes causes these two conditions in differing and independent ways, Dr Abramoff emphasised.

With these subversive results, several more studies were planned – “to both confirm the results in larger groups of subjects, and also to elucidate the mechanism more precisely,” he said.

Dr Abramoff’s team is also investigating if brain damage in diabetes works in a similar way to what they discovered in the eye.