Multimodal Retinal Structural and Functional Tests Identify Local and Layer-Related Alterations in Early Type 2 Diabetes.

Purpose: To use a multimodal approach to provide deeper insights into subclinical, layer-related, and localized retinal structural and functional deficits associated with prediabetes (PreDM) and early type 2 diabetes (T2DM). Methods: Twenty controls, 13 PreDM, and 15 T2DM age-matched (45.58 ± 9.40 years) groups participated. Color perimetry was performed at four locations 3° from fixation, using 0.5° circular red, green, blue, and yellow stimuli. Multifocal electroretinograms (mfERGs) were recorded (103 hexagons), and implicit times (ITs) and amplitudes were averaged and analyzed in ring 2, approximately corresponding to the perimetric testing. Then, 20° optical coherence tomography (OCT) and 10° OCT angiography (OCTA) images were acquired. Perfusion density (PD; all plexuses), retinal layers, and choroidal thicknesses were analyzed (central 2 mm). Results: mfERG P1 ITs were delayed in T2DM (P = 0.03 vs. controls). Thresholds obtained for red increased with delayed P1 ITs (P = 0.02) and with increasing thickness of the inner nuclear layer (P = 0.03). Choroidal thickness showed a negative relationship with blue and yellow thresholds (P < 0.05). Thresholds obtained for red and yellow were higher in the T2DM (all P < 0.05 vs. controls) but green and blue were not (P > 0.05). PD of the intermediate capillary plexus was lower in the T2DM group (P = 0.001 vs. all groups) and was associated with HbA1c (P = 0.02). Conclusions: This combination of tests showed alterations in middle retinal health, which could occur in retinal bipolar cells early in T2DM. A longitudinal investigation would clarify the temporal onset of these neural and vascular changes in the disease process.