Assessment and comparison of the morphology and function of the corneal sub-basal nerve plexus in type-1 diabetes mellitus patients and in healthy subjects

Aim/purpose: It is believed that small nerve bundles are damaged in the earliest stages of neuropathy caused by diabetes mellitus (DM). Our goal was to evaluate and compare anatomical characteristics of corneal nerve fibers and corneal sensitivity in type-1 DM patients and in healthy control subjects.Design: A prospective, masked, controlled cross-sectional clinical study.Method: Thirty patients with type-1 DM and ten non-diabetic healthy subjects underwent a corneal confocal microscopy to evaluate the corneal sub-basal nerve fibers (density, number of nerves and branches, total nerve length) and contact corneal esthesiometry.Results: Diabetic patients had significantly lower corneal nerve fiber density density (14.32 ± 5.87 vs. 19.71 ± 5.59 mm/mm2; p = 0.023 ) nerve branches number (4.57 ± 3,91 vs. 9.90 ± 5.8 n°/image; p = 0.006) , nerve fiber length (2.28 ± 0.94 vs. 3.13 ± 0.89 mm; p = 0.032) and corneal sensitivity (1.13 ± 0.29 vs. 0.98 ± 0.058 gr/mm2 p = 0.02), as compared with controls. A negative correlation was found between corneal nerve fiber length, corneal nerve number, corneal nerve fiber density and disease duration (p < 0.05).Conclusion: Corneal confocal microscopy and corneal sensitivity evaluation are noninvasive techniques helping to detect early changes in the sub-basal nerve plexus characteristic for diabetic neuropathy (DN) in patients with type-1 DM. Further studies are required to investigate the role of corneal neuropathy assessment using these novel techniques as a toll to detect early DN.