Patients with type 2 diabetes likely have reduced corneal nerve fiber lengths (CNFL) compared with healthy individuals, which could contribute to delayed corneal healing and a greater chance of corneal problems after surgery, a new study in Acta Ophthalmologica reports. The investigation also observed a trend in CNFL reduction between individuals with normal glucose metabolism and prediabetes.

A team of researchers from The Netherlands and Italy analyzed corneal confocal microscopy images of CNFL per mm² in the subbasal nerve plexus of the cornea in 134 participants. The patients were about 59 years old, and the study group was mostly split evenly between men and woman. Eighty-seven subjects had normal glucose metabolism, 20 had prediabetes and 27 were diagnosed with type 2 diabetes.

In individuals with type 2 diabetes, the average CNFL was significantly reduced (-1.86 mm/mm²) compared with individuals with normal glucose metabolism after adjustment for age and sex. Researchers noted part of the reduction was present in individuals with prediabetes [(-0.96 mm/mm²), with a trend of CNFL tied to severity of glucose metabolism.

This was the first study that used composite corneal confocal microscopy images to assess the association between glucose metabolism status—as defined by an oral glucose tolerance test—and CNFL, the researchers said. This imaging technique based on real-time mapping of several images allowed the investigators to see a larger continuous surface of the corneal subbasal nerve plexus and, in turn, increased the level of accuracy of CNFL measurements, they added.