Diabetic corneal neuropathy (DCN) and diabetic retinopathy (DR) are microvascular complications of type 2 diabetes mellitus (T2DM) with overlapping pathophysiological mechanisms. To clarify their relationship, investigators conducted a cross-sectional study involving 1,654 eyes from 822 participants, including 634 patients with T2DM and 188 healthy controls. The results were published in Diabetes.

Compared with controls, all patients with diabetes demonstrated significantly impaired corneal nerve metrics, increased dendritic cell length and density, and larger corneal microneuromas, even in the absence of DR. Among diabetic participants, those with nonproliferative DR (NPDR) and proliferative DR (PDR) had significantly reduced corneal nerve parameters compared with patients without DR. Patients with PDR also exhibited significantly worse ocular surface clinical manifestations than patients without DR, those with NPDR, and controls.

Cumulative link mixed models showed that corneal sensitivity and corneal nerve parameters were significantly associated with DR severity. Tear substance P concentrations were significantly lower across all DR stages compared with controls. Additionally, tear MMP-9, substance P, and IGFBP-3 levels were significantly associated with corneal nerve and ocular surface parameters.

Corneal nerve alterations were present in patients with diabetes before the onset of DR and worsened with increasing DR severity. Corneal nerve status may serve as an early indicator and predictor of diabetic retinopathy.