Abstract

The objective of this research was to assess initial neurodegenerative changes in individuals diagnosed with prediabetes, type 1, and type 2 diabetes via optical coherence tomography (OCT). By analyzing the macula, retinal nerve fiber layer (RNFL), ganglion cell–inner plexiform layer (GCL+) and ganglion cell complex (GCL++), we sought to determine structural variations compared to a healthy cohort. This retrospective investigation evaluated the right eyes of 147 subjects aged 18 years and above. The cohort was categorized into four distinct groups: healthy controls, prediabetes, type 1 diabetes mellitus (DM), and type 2 DM. Macular, RNFL, GCL+, and GCL++ thicknesses were quantified utilizing high-resolution scans from a swept-source OCT device. The type 1 DM cohort exhibited significantly greater GCL++ and superior parafoveal (PF) macular thicknesses relative to the control and prediabetic subjects. Conversely, RNFL and GCL+ measurements did not differ significantly among the groups. While GCL++ dimensions showed no notable correlation with Hemoglobin A1c (HbA1c) levels across any category, GCL+ thickness demonstrated a negative correlation in the superior quadrant for healthy controls and a positive correlation in the superotemporal quadrant for the type 2 DM group. These findings imply that traditional atrophic retinal neurodegeneration might not be initiated in these early stages, or that initial metabolic stress merely presents as localized reactive swelling. It appears that early diabetic neural impairment is a reaction to accumulated metabolic stress—rather than sudden glycemic shifts—progressing in a layer-specific manner before any clinical microangiopathy becomes evident.

Key words: Diabetes mellitus, neurodegeneration, optical coherence tomography, prediabetes, retinal ganglion cells