Corneal nerve fibre damage precedes diabetic retinopathy in patients with Type 2 diabetes mellitus

Aims To quantify the morphological alterations in corneal nerve fibres and cells in patients with Type 2 diabetes mellitus in relation to the severity of diabetic retinopathy. Methods One hundred and thirty-two eyes of 132 patients with Type 2 diabetes and 32 eyes of 32 healthy control subjects were evaluated with in vivo corneal confocal microscopy. Patients with diabetes were classified into three groups: patients without diabetic retinopathy, patients with non-proliferative diabetic retinopathy and patients with proliferative diabetic retinopathy. Anterior and posterior stromal keratocyte, endothelial cell and basal epithelial cell densities and sub-basal nerve fibre structure were evaluated. Results Significant reductions in basal epithelial cell, anterior stromal keratocyte and endothelial cell densities were observed only in patients with diabetic retinopathy. However, nerve fibre density, nerve branch density and nerve fibre length were reduced in patients without diabetic retinopathy and worsened progressively with increasing severity of retinopathy. Conclusions Corneal cell pathology occurs in patients with diabetic retinopathy, but corneal nerve fibre damage seems to precede the development of diabetic retinopathy.