Early structural and functional neurovascular changes in the retina in the prediabetic stage.

Purpose: This study was undertaken to investigate the neurovascular changes in the retina of prediabetic subjects.

Methods: Subjects enroled in a prospective study were separated into prediabetic and normal control groups based on their glycosylated haemoglobin (HbA1C) levels, fasting and postprandial blood sugar levels and glucose tolerance test. All the subjects underwent detailed ophthalmic evaluation, which included fundus examination, fundus photography, optical coherence tomography angiography (OCTA), and multifocal electroretinogram (mfERG). Comparisons were done between the groups using the Wilcoxon signed rank test.

Results: The median age was 48 years for the normal controls (n = 40), and 49.5 years for prediabetic subjects (n = 45) (p = 0.306). There was no difference in the vision, contrast sensitivity, thickness of the ganglion cell complex or the foveal avascular zone parameters between the groups. But the central foveal thickness and subfoveal choroidal thickness were significantly reduced in prediabetics (p < 0.01). The mfERG showed significant differences in the amplitude. The average amplitude was 35 ± 12 nv/deg in the normals and 29 ± 11 nv/deg in the prediabetics (p = 0.003). A weak positive correlation was noted between the mfERG and vascular parameters in the prediabetic group.

Conclusions: The prediabetic stage reveals earliest functional neuronal changes in the retina. The neuronal function seems to be affected much earlier than clinically appreciable structural changes in the ganglion cell complex and precedes vascular changes in the retina.